case study questions class 8 chemical effects of electric current

• Chemical Effects of Electric Current Class 8 Case Study Questions Science Chapter 11

Last Updated on September 12, 2024 by XAM CONTENT

Hello students, we are providing case study questions for class 8 science. Case study questions are the new question format that is introduced in CBSE board. The resources for case study questions are very less. So, to help students we have created chapterwise case study questions for class 8 science. In this article, you will find case study questions for cbse class 8 science chapter 11 Chemical Effects of Electric Current.

Table of Contents

Case Study Questions on Chemical Effects of Electric Current

Question 1:

Read the given passage below and answer the question:

Electrolysis is defined as a process of decomposing ionic compounds into their elements by passing a direct electric current through the compound in a fluid form. The cations are reduced at cathode and anions are oxidised at the anode. The main components that are required for conducting electrolysis are an electrolyte, electrodes, and some form of external power source is also needed. Electrolysis is usually done in a vessel named ‘electrolytic cell’ containing two electrodes (cathode and anode) connected to a direct current source and an electrolyte which is an ionic compound undergoing decomposition. In the process of electrolysis, there is an interchange of ions and atoms due to the addition or removal of electrons from the external circuit. Basically, on passing current, cations move to the cathode, take electrons from the cathode (given by the supply source-battery), and is discharged into the neutral atom. The neutral atom, if solid, is deposited on the cathode and if gas, move upwards. This is a reduction process and the cation is, reduced at the cathode. At the same time anions, give up their extra electrons to the anode and is oxidised to neutral atoms at the anode. Electrons released by the anions travel across the electrical circuit and reach the cathode completing the circuit. Electrolysis involves a simultaneous oxidation reaction at anode and a reduction reaction at the cathode.

Q. 1. Which most commonly used liquid is decomposed by the process of electrolysis? (a) Water (b) Petrol (c) Diesel (d) Milk

Difficulty Level: Easy

Ans. Option (a) is correct. Explanation: The decomposition of waterby passing electric current through it is called hydrolysis in which dissociated hydrogen and oxygen appear in form of gas bubbles on the electrode,

Q. 2. Which of the following process is based on the principles of electrolysis? (a) Rusting (b) Colour change of electrolyte (c) Electroplating (d) None of the above

Ans. Option (c) is correct. Electroplating is the process of depositing a layer of any desired metal on another material by means of electricity in an electrolytic cell. Metal ions in the electrolyte decompose on passing electric current and get deposited on cathode forming a thin layer on the metal object.

Q. 3. ____________ is a compound which in aqueous solution that allows an electric current to pass through it while __________are the metal rods which are dipped in electrolyte and attached to external power source. (a) Electrode, electrolyte (b) Anode, cathode (c) Solution, electric plate (d) Electrolyte, electrode

Ans. Option (d) Explanation: Electrolysis is usually done in a vessel named ‘electrolytic cell’ containing two electrodes (cathode and anode) connected to a direct current source and an electrolyte which is an ionic compound undergoing decomposition.

Q. 4. Draw an electrolytic cell.

Difficulty Level: Medium

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Topics from which case study questions may be asked

• Understand the conduction of electricity in liquids.
• Learn about the chemical effects of electric current.
• Know about the process of electrolysis.
• Learn electroplating and its uses.

Some liquids are good conductors of electricity and some are poor conductors. Most liquids that conduct electricity are solutions of acids, bases and salts.

Air is a poor conductor of electricity. But during thunderstorms air acts as conductor and electric current pass through it to reach the Earth. This happens due to a phenomenon termed as Dielectric Breakdown.

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Frequently Asked Questions (FAQs) on Chemical Effects of Electric Current Case Study Questions

Q1: what are case study questions for cbse examinations.

A1: Case study questions in CBSE examinations typically involve scenarios or real-life examples, requiring students to apply their understanding of concepts to solve problems or analyze situations.

Q2: Why are case study questions important for understanding class 8 science chapters?

A2: Case study questions provide a practical context for students to apply theoretical knowledge to real-world situations, fostering deeper understanding and critical thinking skills.

Q3: How should students approach answering case study questions for CBSE?

A3: Students should carefully read the case study, identify the key issues or problems presented, analyze the information provided, apply relevant concepts and principles of sound, and formulate well-supported solutions or responses.

Q4: Are there any resources available online for students to practice case study questions on class 8 science chapters for CBSE exams?

A4: Yes, several educational websites offer case study questions for CBSE students preparing for science examinations. We also offer a collection of case study questions for all classes and subject on our website. Visit our  website  to access these questions and enhance your learning experience.

Q5: How can students effectively prepare for case study questions on Chemical Effects of Electric Current for CBSE exams?

A5: Effective preparation strategies include regular revision of concepts, solving practice questions, analyzing case studies from previous exams, seeking clarification on doubts, and consulting with teachers or peers for guidance and support.

Q6: How can teachers incorporate case study questions on Chemical Effects of Electric Current class 8 science into classroom teaching?

A6: Teachers can integrate case studies into lesson plans, group discussions, or interactive activities to engage students in active learning, promote problem-solving skills, and facilitate a deeper understanding of concepts of sound.

Q7: Why sometimes the bulb in the electric tester in a complete circuit does not glow even if liquid is a good conductor of electricity?

A7: In some situations, even though the liquid is conducting, the bulb may not glow. The bulb in a circuit light up due to the heating effect of electric current. If the current is weak, the filament does not get heated and it does not glow. The current is weak because though a material may conduct electricity, it may not conduct it as easily as a metal

Q8: Distilled water is a bad conductor of electricity. Why does rainwater conduct electricity?

A8: Rainwater contains dissolved salts which conduct electricity. That is why distilled water is a bad conductor of electricity, but rainwater conducts electricity.

Q9: Will an electric device work if we place the positive terminal of a battery towards the negative point of the device? Explain your answer

A9: The electric device will not work as there will be insufficient current flow from the battery to the device.

Q10: Give the full form of LED. Why it is preferable over bulb in testing electric passage through a circuit?

A10: LED is (Light Emitting Diodes), It is preferable than electric bulb because LED glows even if a weak electric current flows through it.

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Case Study Questions for Class 8 Science Chapter 14 Chemical Effects of Electric Current

• Last modified on: 1 year ago
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Here we are providing case study questions for CBSE Class 8 Science Chapter 14 Chemical Effects of Electric Current . We have covered case study questions for all the chapters of Class 8 Science.

Case Study Questions

Question 1:

Sita and her mother reached a jewellery shop to purchase some ornaments. She liked a necklace very much but her mother told her not to purchase it because it is not real gold. When she checked the information tag, it was written that 1gm gold. The necklace was quite big and heavy. She was surprised to see it and asked about it. The salesman explained that it is a gold-plated necklace. Then Sita checked that the process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. It is one of the most common applications of the chemical effects of electric current. Nowadays, people prefer to buy gold-plated jewellery, similarly, iron articles are often coated with zinc or chromium to protect them from rusting and corrosion.

In electroplating factories, the disposal of the used conducting solution is a major concern. It is a polluting waste and specific disposal guidelines should be followed to protect the environment.

Answer the following questions

i) Where and how the electroplating waste should be disposed of?

ii) What are the effects produced by the chemical reactions brought about by an electric current?

iii) Name the materials that can be used for electroplating.

iv) What are the applications of electroplating?

i) Ans: In an electroplating factory, the disposal of the used conducting solution is a major concern because it is a polluting waste, therefore it should be disposed of according to the disposal guidelines of the local authority.

ii) Ans: The passage of an electric current through a conducting solution causes chemical reactions. As a result, bubbles of a gas may be formed on the electrodes. Deposits of metal may be seen on electrodes. Changes in the colour of solutions may occur.

iii) Ans: Common metals used in the electroplating process include black and silver nickel, chromium, brass, cadmium, copper, gold, palladium, platinum, silver, tin and zinc

• Used in jewellery.
• Purification of metals.
• Changing the texture of metal surfaces.
• Preventing corrosion.
• Facilitating conduction in circuit boards.

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Chemical Effects of Electric Current Class 8 Extra Questions Science Chapter 14

October 11, 2019 by Sastry CBSE

Chemical Effects of Electric Current Class 8 Extra Questions Very Short Answer Questions

Question 1. What are good conductors? Answer: The substances that conduct electricity through them are called good conductors.

Question 2. What are insulators or poor conductors? Answer: The substances that do not conduct electricity through them are poor conductors or insulators.

Question 3. Give four examples of conductors. Answer: Copper, iron, aluminium and brass.

Question 4. Give four examples of insulators. Answer: Air, wood, rubber and plastic.

Question 5. Name two metal objects which have a coating of another metal. Answer: Handlebars of bicycles, bathroom taps.

Question 6. What do we get on electrolysis of acidified water? Answer: Hydrogen and oxygen gas.

Question 7. Is air a bad or good conductor? Answer: A bad conductor.

Question 8. Which metal is plated on handle bars of cycles and rim of wheels? Answer: Chromium

Question 9. What is the full form of LED? Answer: Light Emitting Diode.

Question 10. How do we check the electric current? Answer: We check the electric current by using a tester.

Question 11. Which part of an atom is responsible for flow of current? Answer: Electron

Question 12. Why do most liquids conduct electricity? Answer: Due to the presence of ions in them, most liquids conduct electricity.

Question 13. An LED is more efficient device than a bulb. Why? Answer: LED is more efficient because it can glow even when a weak or less current flows through it.

Question 14. Do lemon juice or vinegar conduct electricity? Answer: Yes, they conduct electricity.

Question 15. How is conductivity of liquids tested? Answer: By using a tester.

Question 16. Is water from taps, handpumps, wells and ponds a good conductor? Answer: Yes, water from these sources is a good conductor.

Question 17. What makes distilled water a good conductor? Answer: Salts when mixed with distilled water make it a good conductor.

Question 18. Why is a layer of zinc coated over iron? Answer: To prevent iron from corrosion and rust.

Question 19. Will the solution of sugar in distilled water conduct electricity? Answer: No

Question 20. Why is tin electroplated on iron to make cans used for storing food? Answer: Tin is less reactive than iron. Tin coating prevents food from coming in contact with iron and thus pre¬vents it from getting spoiled or corroded.

Question 21. Why we ifse chromium electroplating on taps and bars of bicycle instead of silver and gold? Answer: Silver and gold are very expensive comparatively to chromium.

Question 22. What type of effect of current do the deposits of metal on electrodes show? Answer: Chemical effect

Question 23. What effect of current does electroplating show? Answer: Chemical effect

Question 24. Which effect of current causes the bulb to glow? Answer: Heating effect

Question 25. Which part of the bulb glows? Answer: Filament

Question 26. Name the three effects of electric current. Answer: Heating, magnetic and chemical effect.

Question 27. How can the magnetic effect of current be checked? Answer: By using magnetic compass.

Question 28. What do we see when the compass needle is brought near a wire in which current is flowing? Answer: The needle deflects.

Question 29. What is electroplating? Answer: Deposition of thin layer of a metal over other metal by electrolysis is called electroplating.

Chemical Effects of Electric Current Class 8 Extra Questions Short Answer Questions

Question 1. Define good conductors and poor conductors or insulators. Answer: The materials that conduct electricity through them are called good conductors whereas those that do not conduct electricity are called poor conductors or insulators. For example, copper, brass, aluminium, iron, etc., are conductors whereas rubber, plastic, wood, air, etc., are insulators.

Question 2. How is the conductivity of liquids tested? Answer: The free ends of the tester is dipped in the liquid. If the bulb glows, the liquid is said to be a conductor. If not, it is an insulator.

Question 4. What is an LED? Why is it preferred to other type of bulbs? Answer: The electric device which is used in the tester instead of bulb is an LED. Its full form is Light Emitting Diode. It is preferred to other bulbs as it can glow even when weak or less current flows through it.

Question 5. Explain the conductivity of water. or Normal water conducts electricity while the pure or distilled water does not. Explain why? Answer: Normal water that we get from sources such as taps, handpumps, wells, ponds, etc., is not pure. It may contain several salts dissolved in it naturally. This water is thus good conductor of electricity. The pure or distilled water is free of salts and is a poor conductor.

Question 6. Give an example of chemical effect of the electric current. Answer: The passage of an electric current through a conducting solution causes chemical reactions as a result, bubbles of a gas are formed, or deposits of metal are seen on electrodes or changes in colour of solution , may occur. These are some of the chemical effects of electric current.

Question 7. What is electroplating? What are its uses? Answer: The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. Electroplating is a very useful process. This is used to make objects appear shiny and resistant to scratches. It prevents corrosion.

Question 8. What happens when electric current is passed through the copper sulphate solution? Answer: When electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it.

Question 9. How does a bulb glow in liquid? Explain. Answer: When the liquid between the two ends of a tester allows the electric current to pass through it, then the circuit of the tester becomes complete and the current flows in the circuit of liquid makes the bulb glow. But when the liquid does not allow the electric current to pass through it, then the circuit of the tester is incomplete and the bulb does not glow.

Question 10. What is the magnetic effect of electricity? Explain. Answer: When electric current is passed through a coil or wire, it behaves like a magnet. This is known as mag¬netic effect of current. It depends on amount of current passing through the coil or wire.

Question 11. Why is magnetic compass needed to test the conduction of electric current? Answer: Sometimes, when the current passing through a conductor is so small that filament of the bulb does not get heated up and the bulb does not glow. In this case, we need magnetic compass to test the conduction of current.

Question 12. What happens when an electric current is passed through a cut potato for a considerable time? Answer: When an electric current is passed through a cut potato for a considerable time, greenish blue spot is formed around positive electrode. The chemical effect of the electric current is involved in this process.

Question 13. Why is chromium used for electroplating? Why the objects have chromium plating are not made of chromium itself? Answer: Chromium has a shiny look. It does not get corroded and it resists scratches. Chromium is however expensive and it may not be economical to make the whole object out of it. So the object is made from a cheaper metal and only a coating of chromium is done over it.

Question 14. Which metals, except chromium, are used for electroplating other metals? Answer: Jewellery makers electroplate silver and gold on ornaments of less expensive metals. Tin cans, used for storing food, are made by electroplating tin onto iron. Tin is less reactive than iron. Hence, food is protected from getting spoilt. Iron used in bridges and automobiles is coated with zinc to protect them from corrosion and formation of rust.

Question 15. Current does not flow in a circuit if there is a gap between the two wires. Does it indicate that air is a poor conductor of electricity? Does air never conduct electricity? Explain. Answer: Air is a poor conductor of electricity if it is dry but in certain cases like during lightning and when air is moist, air may conduct electricity.

Chemical Effects of Electric Current Class 8 Extra Questions Long Answer Questions

Question 1. On what factors thickness of the electroplated items depend? Answer: Thickness of electroplated items depend upon:

• The strength of the current passing through the circuit.
• The concentration of the metal ion in the solution.
• The duration of the time the article has been in the solution.

Question 2. With the help of a suitable diagram, explain electrolytic refining of copper. Answer: To purify copper, a thin plate of pure copper and a thick rod of impure copper are used as electrodes in the acidified solution of CuS04. Pure copper is used as cathode and impure copper is used as anode. When electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it. From impure copper electrode, an equal amount of copper gets dissolved in the solution. Thus, the loss of copper from solution is restored and the process continues. The impurities are left behind at anode.

Question 4. What is electroplating? On which effect of the electric current is it based? Why is it done? Answer: The process of depositing or coating a layer of any desired metal on the surface of other material by means of electricity is called electroplating. It is one of the most common applications of chemical effects of electric current.

Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of a different metal. The layer of metal deposited has some desired property, which the metal of the object lacks. For example, chromium plating is done on many objects to make them shiny and attractive.

Question 5. What are the advantages and disadvantages of electroplating? Answer: Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of different metal. The advantages and disadvantages of electroplating are: Advantages:

• It protects the metals from being corroded.
• It prevents the rusting of metals.
• It makes cheap and dull metals shiny and attractive.
• It can make more reactive metals like iron less reactive.
• Chromium coating on metals give lustre to objects.

Disadvantages

• Pollutants from electroplating industries are very harmful. Some chemicals are very lethal for both human and animals.
• It is an expensive process.

Chemical Effects of Electric Current Class 8 Extra Questions Higher Order Thinking Skills

Question 1. Why electric fires are extinguished with either using CO 2 extinguisher or mud but not water? Answer: As water is a good conductor of electricity so it can cause electrocution. Hence, water is avoided in extinguishing electric fires.

Question 2. Why do you think electroplated jewelleries are in demand? Answer: Electroplated jewelleries are in demand because firstly, they are as shiny and attractive as real jewelleries. They are light-weighted and cost effective. Secondly, one feels free to wear it because of the growing problem of snatching and theft.

Question 3. Do distilled water conduct electricity? What will happen if we add sugar to it and then salt to it? Explain. Answer: No, distilled water do not conduct electricity. If we add sugar to distilled water, then also it will not conduct electricity because sugar do not dissociates into ions. But on adding salt, it will conduct electricity because aqueous salt solution is a good conductor of electricity.

Question 4. Suppose you want to deposit silver on an iron spoon using silver nitrate as electrolyte. Which terminal of the battery you should connect the spoon? What material should the other electrode be made of? Answer: Silver ion is positively charge, so the spoon must be connected to negative terminal to deposit silver on it. The other electrode should be made of silver.

Question 5. Why potato turns green on passing current? Around which terminal greenish patch is observed? Answer: Potato turns green due to chemical effect of current. Around positive terminal greenish patch in potato is observed.

Chemical Effects of Electric Current Class 8 Extra Questions Value-Based Questions

(a) Define a circuit. (b) What does the deflection of a compass needle shows? (c) Why the bulb did not glow in the first case but glow in the second case? (d) What value of Sourav is shown here? Answer: (a) Circuit is a closed path through which an electric current flows. (b) Deflection of compass needle shows that the current is flowing in the circuit. It is magnetic effect of current. (c) The current flowing through the circuit in first case was too low to make the bulb glow but on adding a cell in the second case makes the bulb glow. (d) Sourav is an intelligent, helpful, analytical and with scientific aptitude.

Question 2. While demonstrating an experiment to show whether the given liquid conduct electricity or not to class VIII students, teacher reminded everybody that one should not conduct experiment with the electric supply from the mains or a generator or an inverter. They should use electric cells for the activity. (a) Do liquids conduct electricity? (b) Why we should not use electric source from mains generator or an inverter? (c) What values do we get from this? Answer: (a) Yes, liquids which are solutions of acids, bases and salts conduct electricity. Other liquids such as oil, alcohol, sugar solution and pure water do not conduct electricity. (b) Current flowing from mains, generator or an inverter is very large. So to avoid the chances of elec-trocution and short-circuit we must use cells for experiments. (c) We get awareness of not using main electric supply and precaution to be followed while doing experiment.

Activities and Projects Question 1. Test the conduction of electricity through various fruits and vegetables. Display your re¬sults in a tabular form. Answer: Do it yourself.

Question 2. Repeat Activity 14.7 with a zinc plate in place of the copper plate connected to the negative terminal of the battery. Now replace zinc plate with some other metallic object and again repeat the activity. Which metal gets deposited over which other metal? Discuss your findings with your friends. Answer: When zinc plate is taken as negative electrodes copper ions are deposited on zinc plate. Similarly, the copper ions will be deposited on the plate taken as negative electrode. The process is known as electroplating.

Question 3. Find out if there is a commercial electroplating unit in your town. What objects are electroplated there and for what purpose? (The process of electroplating in a commercial unit is much more complex than what we did in Activity 14.7). Find out how they dispose off the chemicals they discard. Answer: You can find a commercial electroplating unit in your town. Visit the unit and see what objects are electroplated there. Electroplating is a very common and effective method to check corrosjpn, rusting. The surface of iron metal is coated with aluminium, chromium, nickel, etc. Electroplated items are quite resistant to the attack of external agents like acids, water and corrosion. If the surface of metal is electroplated by zinc, it is called galvanisation. Chemicals or electroplating wastes are hazardous to human health and environment. They are managed according to the Hazardous Wastes Rule and treated accordingly before disposal in the environment.

Question 4. Imagine that you are an ‘entrepreneur’ and have been provided a loan by a bank to set up a small electroplating unit. What object would you like to electroplate and for what purpose? (Look up the meaning of‘entrepreneur’in a dictionary). Answer: You can select the objects of your own choice and interest like electroplating jewellery items with gold and silver, wheel rims of vehicles with nickel, etc. It will make the objects shiny, attractive and durable.

Question 5. Find out the health concerns associated with chromium electroplating. How are people trying to resolve them? Answer: The health concerns associated with chromium electroplating are mainly skin diseases, alteration of genetic material, respiratory problems, weak immune system, upset stomach and ulcers. In order to resolve these problems chromium are replaced by mild steel and using water insoluble chromium compounds in factories.

I. Multiple Choice Questions (MCQs) Choose the correct option. Question 1. Which of the following is a bad conductor of electricity? (a) Distilled water (b) Silver nitrate (c) Sulphuric acid (d) Copper sulphate

Question 2. Which of the following does not conduct electricity? (a) Sugar solution (b) Vinegar solution (c) Lemon juice solution (d) Caustic soda solution

Question 3. An electric current can produce (a) heating effect (b) chemical effect (c) magnetic effect (d) all of these

Question 4. Pure or distilled water is a (a) poor conductor (b) good conductor (c) both (a) and (b) (d) none of these

Question 5. Which of the following is a good conductor? (a) Brick (b) Steel (c) Plastic (d) Cotton

Question 6. Polythene is (a) a conductor (b) an insulator (c) both (a) and (b) (d) none of these

Question 7. Electroplating is based on (a) heating effect of electricity (b) chemical effect of electricity (c) physical effect of electricity (d) magnetic effect of electricity

Question 8. Copper is (a) a good conductor (b) an insulator (c) both (a) and (b) (d) none of these

Question 9. Waste from an electroplating factory must be disposed off (a) in the nearby river (b) in the nearby pond (c) in the nearby cornfield (d) according to the disposal guidelines of Waste Management Bodies

Question 10. An electrolyte is (a) a metal (b) a liquid that conducts current (c) a non-metal (d) none of these

Question 11. Flow of electron is called (a) electrolyte (b) electroplating (c) electrodes (d) electric current

Question 12. Which is not a non-electrolyte? (a) Ethyl alcohol (b) Sodium chloride (c) Urea (d) Sodium solution

Question 13. An electric lamp glows due to (a) heating effect (b) magnetic effect (c) chemical effect (d) physical effect

Question 14. Electroplating prevents (a) corrosion (b) passing of current (c) dissociation (d) shining

Question 15. Which of the following is not used for electroplating metal articles? (a) Nickel (b) Silver (c) Chromium (d) Sodium

Question 16. Iron objects can be protected by electroplating them with (a) chromium (b) nickel (c) zinc (d) all of these Answer: 1. (a) 2. (a) 3. (d) 4. (a) 5. (b) 6. (b) 7. (b) 8. (a) 9. (d) 10. (b) 11. (d) 12. (b) 13. (a) 14. (a) 15. (d) 16. (d)

II. Fill in the Blanks Fill in the blanks with suitable word/s. 1. Substances that conduct electricity are called ___________. 2. Substances that do not conduct electricity are called ___________. 3. A cation has ___________ charge. 4. Some liquids are ___________ conductors of electricity and some are ___________ conductors of electricity. 5. Distilled water is an ___________. 6. Distilled water when mixed with salts becomes a ___________ conductor of electricity. 7. Light emitting diodes (LED) glow even when a ___________ electric current flows through it. 8. The passage of an electric current through a conducting solution causes ___________. 9. Change in colour is an example of the ___________ effect of current. 10. There are ___________ wires attached to an LED. 11. In an LED, the longer lead is attached to the ___________ terminal of the battery and the shorter lead to the ___________ terminal. 12. Chromium has a ___________ appearance. 13. Distilled water is made by removing all ___________. 14. Iron tends to ___________ and ___________. 15. A coating of ___________ is deposited on iron to protect it from corrosion and formation of rust. 16. An electric lamp glows due to ___________ effect of electric current. 17. Electrodes are ___________. 18. The deflection in ___________ shows that current is passing. 19. ___________does not corrode easily. 20. An electrolyte is a ___________. Answer: 1 conductors 2. insulator 3. positive 4. good, poor 5. insulator 6. good 7. weak 8. chemical reaction 9. chemical 10. two 11. positive, negative 12. shiny 13. impurities 14. corrode, rust 15. zinc 16. heating 17. conductors 18. magnetic compass 19. Chromium 20. liquid

IV. True or False State whether the given statements are true or false. 1. Rubber is a good conductor of electricity. 2. Plastics are poor conductor of electricity. 3. All liquids conduct electricity. 4. Distilled water is free of salt. 5. Pure water conducts electricity. 6. Most liquids that conducts electricity are solutions of acids, bases and salts. 7. Electroplating is based on magnetic effect of electricity. 8. Small amount of some mineral salts are naturally present in water. 9. Chromium is carcinogenic. 10. An electric bulb glows due to chemical effect of electricity. 11. Distilled water when mixed with salt conducts electricity. 12. LED is an electric bulb which is used in a tester. 13. Deflection in compass needle is due to magnetic effect of current. 14. When electric current is passed through the copper sulphate solution, copper and sulphate ions are dissociated. 15. In an LED bulb, the shorter lead is connected to the positive terminal of the battery. 16. Electric current produces a magnetic effect. 17. Some liquids are good conductors of electricity and some are poor conductors of electricity. 18. Chromium has a shiny appearance. 19. Jewellery makers electroplate silver and gold on expensive metals. 20. Electroplating wastes are useful to human health and environment. Answer: 1. False 2. True 3. False 4. True 5. False 6. True 7. False 8. True 9. True 10. False 11. True 12. True 13. True 14. True 15. False 16. True 17. True 18. True 19. False 20. False

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Important Questions for CBSE Class 8 Science Chapter 14 Chemical Effects of Electric Current

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Important Questions Class 8 Science Chapter 14 – Chemical Effects of Electric Current

Chapter 14 of CBSE Class 8 syllabus is about the Chemical Effects of Electric Current. This chapter explains some important topics, such as-

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• Electricity in liquids.
• Chemical effects of electric current.
• Electroplating.
• Good and bad conductors of electricity.

Students studying science should start by going through the Class 8 Science NCERT textbook. Along with the textbook, it’s important to refer to NCERT exemplar books for solving chapter-specific questions. Science is a practical subject, so along with learning the theory , students can increase their understanding of the concepts by solving various questions from both the NCERT textbooks and exemplars. To get excellent grades in their assignments, tests, and exams  students must also go through Extramarks study materials, including NCERT solutions, CBSE chapter notes, and Important Questions Class 8 Science Chapter 14.

Extramarks thus provide students with a comprehensive list of important exam-oriented questions based on the CBSE syllabus. The Extramarks team refers to NCERT exemplars and textbooks, other important reference books, CBSE sample papers, CBSE past year’s question papers, etc., for collating the questions from all the chapters. Solving a lot of questions provided in our Important Questions Class 8 Science Chapter 14 can make the students feel prepared and confident to answer the different types of questions on their final exams.

Students are recommended to register on the Extramarks website to get access to our comprehensive study materials. They can avail the benefits of solving multiple problems from our solved question bank of Science Class 8 Chapter 14 Important Questions. Along with it, students can refer to other study materials, including NCERT solutions, revision notes, etc.

Get Access to CBSE Class 8 Science Important Questions 2022-23 with Chapter-Wise Solutions

You can also find CBSE Class 8 Science Chapter-by-Chapter Important Questions here:

Chemical Effects of Electric Current Class 8 Extra Questions with Solutions

Extramarks subject experts understand the importance of answering important questions, and we take our role seriously in providing students with the best resources to help them excel academically.Solving problems is one of the most beneficial tools for students who are preparing for mathematics and science exams. We recommend students refer to the Extramarks question bank of Important Questions for Class 8 Science Chapter 14. It is a comprehensive list of questions that will help students understand the exam format and question paper pattern. It comes with fully solved and step-by-step answers prepared by our expert faculty members. So students can use our question bank as a one-stop solution for all subjects to enhance their preparation.

Given below are a few questions and their solutions from our question set of Important Questions for Class 8 Science Chapter 14.

Question 1. What is the full form of the LED? 

• Light Emitting Diode                               
• Light Electricity Device 
• Large Emitting Device                             
• Large Electricity Diode 

Answer 1. A. Light Emitting Diode (LED) is a device that converts electrical energy into light energy.

Question 2. If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the __________terminal of the battery. 

• Positive                               
• Both                            
• None of these

Answer 2. Option B. Negative terminal of the battery attracts Copper ions, and hence copper will get deposited on the plate

Question 3. Which one of the following is a good conductor of electricity? 

• copper                                                        
• distilled water                                           
• none of these 

Answer 3. Option A. Copper is a good conductor of electricity.

Question 4. Electric current produces ______________field. 

• chemical                                    
• physical                                                   

Answer 4 . Option B.

Electric current produces magnetic fields.

Question 5. Define electroplating. 

Answer 5. Electroplating is defined as the process of depositing a layer of any desired metal on another material by using electricity.

Question 6. Write one use of electroplating.

Answer 6. Electroplating is primarily used in industry to coat metal products with a thin layer of a different metal with greater value.

Question 7. Why rubber and plastics do not conduct electricity? 

Answer 7. Rubber and plastics do not allow electric current to pass through them. So they act as insulators and do not conduct electricity.

Question 8. Describe the functioning of a LED. 

Answer 8. The LED stands for light-emitting diode. It detects the weak current in a circuit. A LED has two wires, one wire is slightly longer than the other wire. The longer lead gets connected to the positive terminal of the battery. And the shorter lead gets connected to the negative terminal.

Question 9. Tap water is considered a good conductor of electricity. Why? 

Answer 9. Since tap water is not pure, it includes many mineral salts  such as dissolved sodium, calcium, and magnesium salts, naturally dissolved, making it a good conductor of electricity.

Question 10. Distilled water is a poor conductor of electricity. Justify. 

Answer 10. Distilled water is defined as the water in its purest form. So there are no traces of salts or other dissolved contaminants in pure distilled water. So distilled water is  a poor conductor of electricity.

Question 11. If a small amount of sugar is added to distilled water, will the resulting solution  be a good conductor or a poor conductor of electricity? Explain why. 

Answer 11. As a non-electrolyte material, sugar does not create ions when dissolved in water, making it a bad conductor of electricity. A sugar solution consists of sucrose molecules but no ions. An aqueous sugar solution is a non-electricity conductor fluid because it lacks ions.

Question 12. Fill in the blanks-

(a) Most liquids that conduct electricity are solutions of , ______________ and ______________.

(b) The passage of an electric current through a solution causes ______________ effects.

(c) If you pass current through the copper sulphate solution, copper gets deposited on the plate connected to the ___________terminal of the battery.

(d) The process of depositing a layer of any desired metal on another material using electricity is called _________.

Answer 12. (a) Most liquids that conduct electricity are the solutions of bases, acids and salts.

(b) The passage of electricity through a solution causes chemical effects.

(c) If you pass current through the copper sulphate solution, copper gets deposited on the plate connected to the  negative terminal of the battery.

(d) The process of depositing a layer of any desired metal on another material using electricity is called electroplating.

Question 13. When the free ends of the tester are dipped into a chemical solution, the magnetic needle shows deflection. Can you give  the reason?

Answer 13. The compass needle shows deflection, leading the current flow through the wire. The circuit becomes complete because the free ends of the tester are dipped inside the solution. So, the solution is a conducting solution; deflection is obtained in the compass needle.

Question 14. A tester is used to check the conduction of electricity through two liquids, A and B. It is found that the tester bulb glows brightly for liquid A and very dimly for liquid B. You would conclude that-

(a) liquid A is a better conductor than B.

(b) liquid B is a better conductor than A.

(c) both liquids are equally conducting.

(d) conducting properties of liquid should not be compared in this manner.

Answer 14 . Liquid A is a better conductor as compared to liquid B.

Because the conductivity of the solution determines the amount of current flowing through the solution, the more the conductivity, the greater the quantity of current passing through the solution. The lesser the conductivity, the amount of passing a current through will correspond. Therefore, liquid A’s conductivity is more than liquid B..

Question 15. Can pure water be a conductor of electricity? If not, what can we do to make it a good conductor?

Answer 15. Pure water does not conduct any electricity as it does not contain any kind of salt. Adding some table salt (Sodium Chloride, i.e. NaCl) will change the water into a conducting medium.

Question 16. A child living in the coastal region tests the drinking water and seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason behind it?

Answer 16. The amount of salts dissolved in the seawater is more than that of the drinking water. So, seawater will be a better conductor than drinking water. This is the reason behind the increased deflection of the needle in the seawater compared to the drinking water.

Question 17. Prepare a list of things around you that are electroplated.

Answer 17. Chromium plating- This is done on exterior parts of automobiles to obtain a shiny appearance.

Gold Plating- Silver ornaments are coated with a thin layer of gold, and the product is called Gold-plated Ornaments.

Zinc Plating: Iron used for  construction is coated with a Zinc layer to protect them from corrosion and rusting.

Question 18. Is it safe for the electrician to do electrical repairs outdoors during heavy downpours? Explain.

Answer 18. No, It is not safe for one to repair electrical appliances outdoors during heavy downpours. Rainwater is composed of some amount of dissolved salts that make it conductive. This can cause electric shocks and harm the electrician while working outdoors during heavy downpours.

Question 19. An electric current can produce

(a) the heating effect only.

(b) the chemical effect only.

(c) the magnetic effect only.

(d) chemical, heating, and magnetic effects.

Answer 19. The answer is option (d) chemical, heating, and magnetic effects.

Explanation: Electric current causes a chemical reaction through a conducting solution. This shows the chemical effect of electric current.

When electricity passes through the bulb, its filament gets heated, and the bulb starts to glow. This shows the heating effect of electric current.

When electricity is passed through a circuit, it generates a magnetic field around it. This shows the magnetic effect of electric current.

Question 20. Boojho’s uncle has established an electroplating factory in his village. He should dispose waste of from the factory-

(a) in the nearby river.

(b) in the nearby pond.

(c) in the nearby cornfield.

(d) according to the disposal guidelines of the local authority.

Answer 20. The answer is option (d) according to the disposal guidelines of the local authority.

Explanation- Waste disposal is a significant concern in the electroplating industry as it causes water pollution and releases hazardous chemicals into water resources. Hence it should be disposed of as per the local authority’s guidelines.

Question 21. When an electric current is passed through a conducting solution, there is a change in the colour of the solution. This shows-

(a) the chemical effect of current.

(b) the heating effect of current.

(c) the magnetic effect of current.

(d) the lightning effect of current.

Answer 21. The answer is option (a) the chemical effect of current

Explanation- Conducting a solution through electric current causes  chemical reaction. This results in  a colour change, the electric current’s chemical effect.

Question 22. Paheli wants to coat silver on an iron spoon. She took some amount of silver nitrate (AgNO3) solution in a beaker and set up a simple circuit for electroplating. Explain which terminal of the battery the spoon should be connected to. What material should be used for the other electrode?

Answer 22. The spoon must be connected to the negative end of the battery. The other electrode should  be made of silver.

Question 23. Why is tin electroplated on iron to make the cans used for storing food?

Answer 23. Tin is less reactive than iron. To prevent iron from reacting with the food, tin is coated with  iron to make the can ideal for storing food.

Question 24. An electric current is passed into a conducting solution. What can be the three possible observations?

Answer 24. Few possible observations when electric current is passed through any conducting solution are.

i) Bubbles of gas can be formed on the electrodes and deposits of metal may also be seen on electrodes.

ii) The solution may get heated.

iii) There can be a change in the colour of the solution.

Question 25. In a circuit, Boojho observed that copper is deposited on the electrode connected to the battery’s negative terminal. Paheli also repeats the same experiment. But she finds only one copper plate. Therefore she takes a carbon rod as the negative electrode. Will copper still be deposited on the carbon rod? Explain your answer.

Answer 25. Copper from the copper sulphate(CuSO4) solution will be deposited on the carbon rod. Copper sulphate splits into copper and sulphate when an electric current is passed through the copper sulphate solution. The free copper gets drawn to the electrode connected to the battery’s negative terminal, i.e. carbon rod, and gets deposited on it. Thus, Paheli will obtain a layer of copper on a carbon rod.

Question 26. If the plus sign (+) denotes the positive electrode and the minus sign (-) indicates the negative electrode, then which of the following statements is correct for an iron spoon to be copper-plated?

(a) copper plate (-), Iron spoon (+), Iron sulphate electrolyte

(b) copper plate (+), Iron spoon (-), Iron sulphate electrolyte

(c) Copper-plate (-), iron spoon (+), copper sulphate electrolyte

(d) iron spoon (-), Copper Plated (+), copper sulphate electrolyte

Answer 26 . Option (d) is the answer.

Question 27. Explain the process of electroplating with an experiment.

Answer 27. Copper sulphate and two copper plates are required. Take a clean and dry beaker, and pour around 250 ml of distilled water. Two spoons of copper sulphate should be dissolved in it. Add drops of dil. Sulphuric acid (H2SO4) to make the copper sulphate solution more conductible. Using sandpaper, clean the copper plates. After this, give them a good rinsing and allow them to air dry. Dip the copper plates in a copper sulphate solution after connecting them to both ends of a battery. Allow 15 minutes for the electric current to pass through it. Now, take the electrodes out and observe them closely. When an electric current is given to the solution, copper sulphate dissociates into copper and sulphate. The free copper metal is attracted to the electrode linked to the battery’s negative terminal and deposited there.

Question 28. Vinegar is a sour liquid state. Does vinegar conduct electricity or not?

Answer 28. Vinegar is a bad conductor of electricity because it has no free ions to carry an electric charge and conduct electricity.

Question 29. How would you classify lemon juice- as a good conductor or a poor conductor of electricity?

Answer 29. Lemon juice is a conductor of electricity because it has citric acid having positively charged ions responsible for the conduction.

Question 30. Write the name of a device which glows even when a weak electric current passes through it.

Answer 30. A Light Emitting Diode (LED) glows even if a weak current passes through it.

Question 31. What should be done to decompose water into hydrogen and oxygen?

Answer 31 . We should pass an electric current into the water to decompose water into hydrogen and oxygen.

Question 32. Name the metal usually electroplated on car parts such as bumpers and bicycle handlebars made of steel.

Answer 32 . Chromium metal is electroplated on car parts such as bumpers and bicycle/ motorcycle handlebars made of steel.

Question 33. What is the common use of the chemical effect of electric current?

Answer 33. The most common example of the chemical effect in electric currents is-

Gold plating and chromium metal plating prevent corrosion.

Question 34. Which is the polluting waste generated by electroplating factories?

Answer 34. The conducting solution which is used in the electroplating process is the final waste that is generated by electroplating factories.

Benefits of Solving C lass 8 Science Chapter 14 Important Questions

Science syllabus of Classes 6, 7, 8 and 9 forms fundamental knowledge for higher classes. So students should focus on understanding the concepts of each topic in depth so that they have practical as well as  theoretical knowledge. A lot of practice and consistent effort must go towards understanding the core concepts of Science.

Our question bank of Important Questions Class 8 Science Chapter 14 is a comprehensive set of exam-oriented questions that are curated from various past years’ exam papers, NCERT exemplar and textbooks, and other Science reference books.

Extramarks believes in incorporating the best learning experiences through its own repository.To enjoy the maximum benefit of these resources, students just need to register themselves at Extramarks official website and stay ahead of the competition. Here we have given few benefits that students can  avail  by solving questions from our question bank of Important Questions Class 8 Science Chapter 14:

• The questions are curated and made from the exam point of view. Thus, students get exposure to real examinations while solving these questions. So it helps them to get rid of their fear factor and enhances their confidence while answering questions during  exams with greater accuracy. And speed..This helps them  to master the topic and increases their confidence in achieving a high grade.
• Important Questions Class 8 Science Chapter 14 offer students a comprehensive learning pattern to provide a smooth and deep learning experience to the students while solving questions of varying levels of difficulty.
• The list of   Important Questions Class 8 Science Chapter 14 includes a comprehensive list of questions from the entire chapter. So by properly solving all questions from the question bank students will be able to revise Chapter 14 fully. They would also be able to self-assess their readiness by comparing their answers with the given solutions. Based on this they can further work on their weaker sections.

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Q.1 Virus are living or non-living. Comment with reasons.

Marks: 2 Ans

Viruses are considered as the connecting link between living and nonliving. 1. They can be considered nonliving as they neither grow nor reproduce once out side the host. 2. They can be considered living as they multiply very fast and grow when entered the host.

Q.2 (i) In which form nitrogen is taken by the plants from the soil (ii) Why nitrogen fixation is necessary

(i) Atmospheric nitrogen is converted into NH 3 by certain bacteria. Plants cannot use atmospheric nitrogen directly. Nitrogen is taken up by plants as ammonia or nitrates. (ii) Nitrogen fixation is necessary because plants and animals are not able to use atmospheric nitrogen directly. In nitrogen fixation process, nitrogen is taken from its natural, relatively inert molecular form (N 2 ) in the atmosphere and converted into usable nitrogen compounds.

Marks: 3 Ans

Certain symbiotic bacteria ( Rhizobium) present in the roots of leguminous plants (example, pulses and peas) convert the atmospheric nitrogen into soluble nitrates and other nitrogenous compounds so that plants can easily utilise the atmospheric nitrogen.

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Important questions for class 8 science, chapter 1 - crop production and management.

Chapter 2 - Microorganisms: Friend and Foe

Chapter 3 - synthetic fibres and plastics, chapter 4 - materials: metals and non metals, chapter 5 - coal and petroleum, chapter 6 - combustion and flame, chapter 7 - conservation of plants and animals, chapter 8 - cell - structure and functions, chapter 9 - reproduction in animals notes, chapter 10 - reaching the age of adolescence, chapter 11 - force and pressure, chapter 12 - friction, chapter 13 - sound, chapter 15 - some natural phenomena, chapter 16 - light, chapter 17 - stars and the solar system, chapter 18 - pollution of air and water, faqs (frequently asked questions), 1. where can students easily find important questions class 8 science chapter 14.

To make it easier for students to learn, revise and prepare for their examinations, Extramarks provides a list of Important Questions in Class 8 Science Chapter 14. With this comprehensive list of questions prepared by experts, topics from all  the chapters are covered, thus ensuring that the students achieve better grades in their examinations. You can be rest assured as you get authentic and reliable solutions to the chapter 14 Class 8 Science important questions.

2. What are the important chapters covered in Class 8 Science?

The subject of Science is essential to create a strong base for Class 8 and further higher studies, and every chapter plays a vital role. The important chapters covered in Science for Class 8 include-

• Crop production and Management.
• Microorganisms: Friend or Foe.
• Synthetic Fibres and Plastics
• Materials: Metals and Non-Metals.
• Coal and Petroleum.
• Combustion and Flame.
• Conservation of Plants and Animals.
• Cell – Structure and Functions.
• Reproduction in Animals.
• Reaching the Age of Adolescence.
• Force and Pressure.
• Chemical Effects of Electric Current.
• Some Natural Phenomena.
• Stars and The Solar System.
• Pollution of Air and Water.

3. What unique characteristics does the Extramarks study material of Class 8 Science Chapter 14 Important Questions have?

The following are the unique characteristics of the Important Questions Class 8 Science Chapter 14 available on Extramarks:

• It has practice questions that cover the entire chapter. Going through these questions can also prove to be a good revision of the chapter.
• Important questions Class 8 Science Chapter 14 provides you with a wide range of questions for better revision and also provides in-depth knowledge of the concepts.
• The expert provided solutions for maximum reliability and error-free solutions.
• Easy to understand solutions in simple language for self-study without having to look elsewhere for any study materials.

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Chemical Effects of Electric current Class 8 Important Questions and Answers

Important questions of Class 8 Science Chapter 14 Chemical Effects of Electric current is given below. These important questions will help students while preparing for the exam.  Practising these important questions will analyse their performance and work on their weak points. Score well in exam of Class 8 Science by going through these important questions. Students of Class 8 can download important questions of Class 8 Science Chapter 14 Chemical Effects of Electric current PDF by clicking the link provided below.

Important Questions of Class 8 Science Chapter 14 Chemical Effects of Electric current

Here you can get  Class 8 Important Questions Science  based on NCERT Text book for Class 8. Science Class 8 Important Questions are very helpful to score high marks in board exams. Here we have covered Important Questions on  Chemical Effects of Electric current  for Class 8 Science subject.

Very Short Answer Questions

1. What is electricity?

Answer: Electricity is a phenomenon known for its effect like chemical effect, Heating effect and magnetic effect.

2. What is the cause of electricity?

Answer: The flow of charge is the main cause of electricity. 

3. What is charge?

Answer: The fundamental properties of matter caused by gain or loss of electrons.SI unit of charge is Coulomb or C

4. What is the charge on 1 electron? Answer: 1.6 × 10 -19 C

5. What are the two types of electricity on the basis of charge?

Answer: The two types of electricity on the basis of charge are: (a) Static electricity: The electricity cause by the charge at rest. (b) Current electricity: The electricity cause by the charge when in motion

6. What is the cause of the flow of charge?

Answer: Electric potential or potential difference is the main cause of electric charge.

7. What do you mean by chemical effect of current?

Answer: The phenomenon of causing chemical change by passing electric current through a conduction solution is called chemical effect of current. For example: Electrolysis and Electroplating

8. What do you mean by heating effect of current?

Answer: Whenever current flows through a conductor it causes heating of material. This effect of current is known as heating effect of current.

9. What do you mean by magnetic effect of current?

Answer: Whenever current flows through a conductor it behaves like a magnet. This effect of current is known as magnetic effect of current.

10. What is LED? Answer: LED stands for Light Emitting Diode. LED glows even when a weak electric current flows through it.

11. What precaution you should take to add LED in a circuit?

Answer: The longer lead is always connected to the positive terminal of the battery and the shorter lead is connected to the negative terminal of the battery.

12. What are good conductors? Answer:  The materials which allow electric current to pass through them are called good conductors of the electricity.

13. Give two examples of good conductors of electricity. Answer:  Copper, iron.

14. Why is it dangerous to touch an electrical appliance with wet hands? Answer:  Wet hands act as good conductors. So we feel electric shocks when we touch electric appliance with wet hands.

15. What are insulators (poor conductors) of electricity? Answer:  The materials which do not allow electric current to pass through them are called poor conductors.

16. Give two examples of poor conductors of electricity. Answer:  Dry wood, rubber.

17. What is electric current? Answer:  The flow of charges (electricity) is called electric current.

18. Do liquids conduct electricity? Answer:  Yes, liquids also conduct electricity.

19. How can you check current? Answer:  We check current by using tester.

20. Give any liquid conductor. Answer:  Tap water. 

21. Can distilled water conduct electricity? Answer:  No, distilled water cannot conduct electricity.

22. How can we test that liquids conduct electricity? Answer:  We use tester to check that the liquids conduct electricity.

23. Name some substances which make the liquids good conductor of electricity. Answer:  Acids, Bases and Salts.

24. Name two liquid substances other than water which conduct electricity. Answer:  (i) Lemon Juice (ii) Vinegar.

25. Sometimes even though the liquid is conducting, the bulb may not glow. Give reason. Answer:  Sometimes the bulb does not glow because the current through it is too weak to make the bulb glow.

26. Which effect of current causes the bulb to glow? Answer:  Heating effect.

27. Name the part of bulb which glows. Answer:  Filament.

28. What is LED? Answer:  LED is a device or bulb which glows even at low or small current.

29. Write full form of LED. Answer:  Light Emitting Diode.

30. What are the three effects of electric current? Answer:  There are three effects of electric current—heating, magnetic and the chemical effect.

31. What is magnetic effect of electric current? Answer:  The electric current also produces the magnetic effect by which a current carrying wire behaves like a magnet.

32. What happens when a compass needle is brought near a wire in which current is flowing? Answer:  The needle deflects.

33. How can we check magnetic effects of current? Answer:  By using magnetic compass.

34. Does distilled water conduct electricity? Answer:  No, distilled water does not conduct electricity.

35. How can we make distilled water a good conductor of electricity? Answer:  By adding some salt in distilled water.

36. What is distilled water? Answer:  The water which is free of salts is called distilled water.

37. Name a salt which makes distilled water a good conductor of electricity. Answer:  Common salt.

38. What are electrodes? Answer:  The metal rods dipped in liquids to which cells are attached are called electrodes.

39. Name the gases which release when current is passed through water. Answer:  Hydrogen and oxygen.

40. Name the gas deposited on negative electrode. Answer:  Hydrogen.

41. Name the gas deposited on a positively charged electrode. Answer:  Oxygen.

42. Name the process that shows the chemical effect of electricity. Answer:  Electroplating.

43. Define electroplating. Answer:  The coating of a layer of desired metal on other metallic surface by passing electric current is called electroplating.

44. Is air a conductor or an insulator? Answer:  Insulator.

Short Answer Type Questions

1: Differentiate between good conductors and bad conductors of electricity.

2: Describe an electrical tester.

Answer:  An electrical tester is a simple piece of electronic test equipment used to determine the presence or absence of an electric voltage in a piece of equipment under test. It is also used to test whether a liquid allows electric current to pass through it or not.

3: How can we check whether a tester is working or not?

Answer:  Join the free ends of the tester together, for a moment, and check whether the bulb glows or not, if the bulb glows it means tester is working and if not it means tester is not working. In case it does not glow check that all connections are tight, or not.

4: How can you test whether lemon juice is good conductor or poor conductor of electricity?

Answer:  Pour one table spoon of lemon juice in a plastic cap of discarded bottle, dip the end of tester into lemon juice, make sure that the tester should not more than 1 cm apart at also should not touch each other, we will observe the current flows in the circuit and bulb glows, this proves that lemon juice is good conductor.

5: In some situation even liquid is allowing the electric current to pass but, bulb does not glow. Why so?

Answer:  This happens when current through the circuit is too weak to make the bulb glow.

6: Why the filament of bulb does not get heated sometimes in a circuit?

Answer:  This is because current through the circuit is too weak so the filament of the bulb does not get heated sufficiently and it does not glow.

7: Is it possible for an electric tester to detect weak current also, if no how can we detect weak current flowing in a circuit?

Answer:   If weak current flows through the circuit then bulb in it will not glow. In order to detect weak current we use LED or may use another effect of electric current that is it produces magnetic effect also so we can use this property of electric current to detect weak current.

8: Why materials classified as poor conductors, also allow electricity to pass under certain conditions?

Answer:  Under certain condition most of the materials can conduct electricity thus it is right to say poor conductors instead of bad conductors or insulators.

9: Distilled water is good conductor or bad, how can we make distilled water a good conductor?

Answer:  Distilled water is a poor conductor but if we add some salt in it the resulting salt solution is good conductor.

10: Explain the functioning of a LED.

Answer:  LED stands for Light emitting diode. It is a semiconductor light source, use to detect weak current in the circuit. There are two wires attached to a LED, one lead is slightly longer than the another one, the longer lead is always connected to the positive terminal of battery and shorter lead is connected to negative terminal of battery

11: What are the purpose of one longer and another shorter lead of a LED?

Answer:  the longer lead is always connected to the positive terminal of battery and shorter lead is connected to negative terminal of battery.

12: Why tap water is always good conductors?

Answer:  Tap water is not pure, it contains several amounts of mineral salts naturally dissolved in it, thus it is a good conductor.

13: Why water that we get from ponds and hand pumps are always good conductors?

Answer:  Water that we get from ponds and hand pumps is not pure, it contains several amounts of mineral salts naturally dissolved in it , thus it is good conductor.

14: We add small amount of dilute hydrochloric acid to distilled water, the resulting solution will be a good conductor or poor conductor? Explain why.

Answer:  Good conductor, because when we add kitchen salt (NaCl) to the distilled water the salt dissolves in water by splitting its molecules in ions:

H 2 O + NaCl→ H 2 O + (Na + ) + (Cl – ) 

The NaCl molecules react to give ions. This happens because the NaCl is a strong electrolyte. Solutions of strong electrolytes are good conductors of electricity because they contain a relatively high concentration of ions.

15: We add small amount of sugar to distilled water, the resulting solution will be a good conductor or poor conductor? Explain why.

Answer:  Poor conductor, because Sugar, as a non-electrolyte substance, does not produce ions when dissolved in water. A solution of sugar contains molecules of sucrose, but no ions. The absence of ions in a sugar aqueous solution makes it a non-electricity conductor fluid.

16: What happens when electrodes are immersed in water and a current is passed?

Answer:   When electrodes are immersed in water and a current is passed bubbles of oxygen and hydrogen is produced. 17: What do you mean by gold plating?

Answer:  Gold plating is one of the most common applications of electroplating in ornament-making.

18: Define electro- magnetic induction.

Answer:  In a circuit the induced current flowing through the coil is always such that it opposes the motion of the magnet. This process of producing induced current due to a varying magnetic field is called electro- magnetic induction.

19: What do you mean by electrolysis and electrolytes?

Answer:   Electrolysis:  The passage of an electric current through a liquid causes chemical changes. This process is known as electrolysis.

Electrolytes:  Conduction is possible only in those liquids which are at least partly dissociated into oppositely charged ions; such liquids are called electrolytes. Solutions of many inorganic chemical compounds (e.g. common salt, sulphuric acid, etc.) are examples of this type of liquid.

20: What do you mean by voltameter?

Answer:   Voltameter:  In electrolysis, the whole arrangement of electrodes, electrolyte and the vessel containing them is called a voltameter. In the case of the copper voltameter, which involves copper electrodes in copper sulphate solution, the net effect is that copper is dissolved off the anode and deposited on the cathode, with the electrolyte remaining unchanged. 21: When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain why?

Answer:  The deflection through the compass needle shows that current is flowing through the wounded wire and hence through the circuit. The circuit is complete since free ends of the tester are dipped in the solution and the solution is certainly conducting solution. 22: In case of fire before the fireman used the water hoses, they shut off the main electrical supply of the area, why so?

Answer:  Water may conduct electricity, if the electrical supply of the area is not shut off and water is poured over electrical appliances then electricity may pass through fire and may harm the fireman, thus In case of fire before the fireman used the water hoses, they shut off the main electrical supply of the area

23: In which case the compass needle will deflect more: by testing sea water or by testing drinking water?

Answer:  The compass needle will defect more in case of sea water than drinking water because sea water contains more dissolved salt than the drinking water.

24: It is said that rain water is as pure as distilled water, but once while testing rain water compass needle shows deflection, explain why?

Answer:  This is because rain water contains dissolved salts that makes it a conducting solution.

26: Differentiate between conductors and insulators.

Answer:  The substances which allow the electric current to pass through them are called conductors. Example metals like copper, aluminium. The substances which do not allow electric current to pass through them are called insulators, example : rubber, wood

27: Write some of the chemical effects of electric current. What causes the chemical reactions in a conducting solution?

Answer:  The passage of an electric current through a conducting solution causes chemical reactions. Following are listed some of the chemical effects of electric current:

• Bubbles of a gas may be formed on the electrodes.
• Deposits of metal may be seen on electrodes.
• Changes of colour of solutions may occur.
• In fact, the reaction would depend on what solution and electrodes are used.

28: Is it safe for an electrician to carry out electrical repairs outdoors during heavy downpour? Explain.

Answer:  No, it is not at all safe for an electrician to carry out electrical repairs during heavy downpour. Rather, it is highly dangerous, because during heavy downpour there is a high risk of electrocution.

29: What do you mean by electric current?

Answer:  The continuous and directional flow of charges (electrons) is called electric current. It is denoted by I and its unit is ampere.

30: What is a tester?

Answer:  The instrument which is used to check the flow of electric current is called tester. It is attached to the terminals of the electric circuit. If the bulb of tester glows, it confirms that current is flowing through the circuit. 

31: How can you test whether the liquids conduct or do not conduct the electricity?

Answer:  Some liquids are the good conductors of electricity while some are poor conductors. The liquids can be tested for conductor of electricity. The free ends of a tester are dipped in liquid to be tested and then observe the bulb, if it glows, it confirms that the liquid is good conductor otherwise liquid is a poor conductor. 

32: Show that lemon juice and vinegar are good conductors of electricity.

Answer:  Collect a few plastic or rubber caps of bottles. Pour one teaspoon of lemon juice or vinegar in one cap. Bring the tester over the cap and let the ends of the tester dip into lemon juice or vinegar. We see that bulb starts to glow. It indicates that lemon juice and vinegar are good conductors of electricity.

33: Explain the mechanism of glowing of bulb in liquid. Answer:  When the liquid between the two ends of a tester allows the electric current to pass, the circuit of the tester becomes complete. The current flows in the liquid circuit and the bulb glows. When the liquid does not allow the electric current to pass, the circuit of the tester is not complete and the bulb does not glow.

34: There are some situations in which even though liquid is conducting, bulb may not glow. Give reasons.

Answer:  The possible reasons may be: (i) The current may be weak. (ii) Bulb may be fused. (iii) Incomplete circuit.

35:  Explain why a bulb glows on passing current.

Answer:  When the current passes through a bulb, the filament of the bulb gets heated to a high temperature due to the heating effect of current. The bulb starts to glow. Sometimes the current is too weak and filament does not get heated sufficiently and bulb does not glow.

36: What is LED? Why is it most important source of light?

Answer:  The device which is used in the tester in place of bulb is called LED. It glows even at very small current. There are two wires called leads attached to the LED. One lead is longer than the other. A long wire is connected with the positive terminal and shorter lead is connected to the negative terminal of battery.

37: What do you mean by magnetic effect of electricity?

Answer:  When electric current is passed through a coil or wire, then it behaves like a magnet. This is called magnetic effect of current. The strength of magnetic field depends on the amount of current passing through a coil or wire. The coil or wire shows magnetism till current is passed.

38: The ordinary water can conduct electricity while distilled water does not. Explain why.

Answer:  The water that we get from various sources like taps, hand pumps, wells and ponds is not pure. It may contain several salts dissolved in it. This water is thus good conductor of electricity. Distilled water is free of salts due to which it is a poor conductor.

39: Why do we need magnetic compass to test the conduction of electric current?

Answer:  Sometimes the bulb does not glow on passing electric current. This is because the electric current flowing through a conductor is so small, that the filament of the bulb does not get heated up to the temperature where it starts glowing. So, in case of small current we need magnetic compass to test the conduction.

40: What is chemical effect of electricity? Give some examples of chemical effects.

Answer:  The process in which a chemical reaction or change takes place in a solution on passing electricity is called chemical effect of electricity. The passage of an electric current through a conducting solution causes chemical reactions. For example, change in colour of solutions and electroplating.

Long Answer Type Questions

1: Explain the process of electroplating, along with its advantages and uses.

Answer:   One of the most common applications of the chemical effect of electric current is electroplating. In this process, there exists a liquid, usually called the electrolyte, through which current passes. Two electrodes, connected to the terminals of a battery with a switch in between, are inserted in the liquid. The electrode that is connected to the positive terminal of the battery is called the “anode,” and the other connected to the negative terminal is called the “cathode”. Electroplating is done in industries to have an anti-reactive coating on the parts of machines so that they do not react with the raw material, to have an anti-corrosive coating for the machines so that they do not get corroded, and a heat-resistive coating for parts like boilers to resist the heat produced by the machinery. The process of electroplating is used for plating parts of vehicles with nickel and chromium, which protects them from corrosion.

2: Most liquids that conduct electricity are solutions of acid, bases and salt . Justify the statement.

Answer:  Good conductor, because When we add kitchen salt (NaCl) to the distilled water the salt dissolves in water by splitting its molecules in ions:

H 2 O + NaCl → H2O + (Na+) + (Cl-) 

Poor conductor, because Sugar, as a non-electrolyte substance, does not produce ions when dissolved in water. A solution of sugar contains molecules of sucrose, but no ions. The absence of ions in a sugar aqueous solution makes it a non-electricity conductor fluid. 3: Prepare a tester to test conduction based on magnetic effect of the electricity.

Answer:  Take the tray of a discarded matchbox. Wrap an electric wire a few times around the tray. Place a small compass needle inside it. Now connect one free end of the wire to the terminal of a battery. Leave the other end free. Take another piece of wire and connect it to the terminal of battery. Join the free ends of two wires momentarily. The compass needle should show deflection. The tester with two free ends of wire is ready. 

4: Complete the following table and classify the liquids by using tester.

  Answer:

5: What are the two methods of testing an insulator or a conductor?

Answer:  The following two methods are used to test the conduction. (i) We use an electric lamp to test conductivity. An electric lamp is attached to the electric circuit. If the substance allows the current to pass through it, the bulb will start glowing. Otherwise, the bulb will not glow. This method does not work when current is very small. In such cases magnetic compass is used. (ii) A magnetic tester is used to test conductivity when current is allowed to pass through it, it creates a magnetic field and the compass shows deflection. The deflection of compass shows that the current is passing through circuit (See Fig.).

6: What do you mean by electroplating? How does it take place?

Answer:  The process of coating a desired metal on other metal surface by using electric current is called electroplating. A metal plate and the substance to be coated are dipped in a current conducting solution with conducting wires. The object to be coated is attached to the negative terminal. When electric current is passed through the solution, the compounds of the conducting solution start breaking. The free metallic particles get deposited on the object at negative terminal of the battery. In this way we can get a coating of desired metal on any object by preparing suitable conducting solution and by using suitable electrodes.

7: Explain the advantages of electroplating.

Answer: The advantages of electroplating: (i) It is used to coat a desired metal on other objects. (ii) It protects the metals from corrosion. (iii) It also prevents the metallic surfaces from rusting. (iv) Some cheap and dull metals are coated with costly and shiny metals. (v) It can make more reactive metals like iron, less reactive. (vi) Coating of chromium on metals give lustre to objects.

8: Explain the process of electroplating.

Answer:  One of the most common applications of the chemical effect of electric current is electroplating. In this process, there exists a liquid, usually called the electrolyte, through which current passes. Two electrodes, connected to the terminals of a battery with a switch in between, are inserted in the liquid. The electrode that is connected to the positive terminal of the battery is called the “anode,” and the other connected to the negative terminal is called the “cathode”. Electroplating is done in industries to have an anti-reactive coating on the parts of machines so that they do not react with the raw material, to have an anti-corrosive coating for the machines so that they do not get corroded, and a heat-resistive coating for parts like boilers to resist the heat produced by the machinery. The process of electroplating is used for plating parts of vehicles with nickel and chromium, which protects them from corrosion.

9: Can you prepare an electric pen? Describe how?

Answer:   Take a filter paper and soak it with potassium iodide and starch solution.

• Spread this filter paper on a metal sheet.
• Now take two connecting wires and join them to the terminals of battery.
• Attach the wire connected at positive end to plate.
• Now write on the sheet wire attached to negative terminal.

We will see that wherever we write, blue coloured ink will appear. The reason for this is electrolysis of potassium iodide solution which produces iodine. Iodine on reaction with starch produces ink of blue colour.

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Chapter 14 Class 8 - Chemical Effects Of Electric Current

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Get NCERT Solutions and Notes of Chapter 14 Class 8 Science - Chemical Effects of Electric Current. At Teachoo, we first explain the concepts... and then we solve the questions related to that concept.

In this chapter, we will learn

Good and bad conductors of electricity

Do liquids conduct electricity

Is Water a Good Conducto r of Electricity?

Electrolytic Cell

What are Different Chemical Effects of Electric Current ?

Electroplating

Different Types of Electroplating

In addition to the Concepts, and the Solutions of NCERT Questions.

We also made Extra Questions for your practice and revision. Some of the extra questions are

Is Vinegar a good conductor of electricity?

Is Vegetable Oil a good conductor of electricity?

What is the difference between Cell and Battery ?

What is the difference between solids and liquids conducting electricity ?

What is the full form of LED, LCD, MCB, USB, CFL, CFC

Why is tin electroplated on iron to make cans used for storing food?

What is the difference between an insulator and a bad conductor of electricity?

How to detect weak current flowing through liquid ?

Why is Distilled water not a good conductor of electricity? What can be done to make it conducting?

How do we dispose used conducting solution from factories?

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Chemical Effects of Electric Current

3.1 ELECTRIC CURRENT

The rate of flow of charge in a circuit is called electric current. In other words, it is the amount of charge flowing per second. Denoted by letter I.

If Q is the charge which is flowing through a conductor in time t, then current is given by i = Q t

Unit of Current The S.I unit of current is ampere and it is denoted by the letter ‘A’. The S.I unit of Q is coulomb and that of t is second. Thus, the S.I unit of electric current is 1  coulomb  1  second  = 1 A

Definition of Ampere When a charge of coulomb flows through a conductor in one second, then the current flowing through the conductor is said to be one ampere. Thus, when 1 coulomb of charge flows through a conductor in 1 second, then the current flowing through it is said to be 1 ampere.

1  ampere  = 1  coulomb  1  second 

Smaller units of Electric Current Sometimes smaller units of current are also used. These are microampere and milliampere. 1 microampere = 1 μ A = 10 – 6   A 1 milliampere = 1   mA = 10 – 3   A

Bigger unit of electric current: Sometimes the magnitude of the current flowing in a conductor is very large. This large magnitude of current is expressed in bigger units, such as kilo ampere and mega ampere. 1 kilo ampere (kA) = 1000 A = 10 3 A 1 mega ampere (MA) = 1,000,000 A = 10 6 A

Flow of Current In metals, the moving charges are the electrons constituting the current, while in electrolytes and ionized gases, electrons and positively charged ions are the ions moving charges which constitute current. The charge on an electron is negative and is – 1 . 6 × 10 – 19 coulomb (symbol C). Therefore, IC charge is carried by electrons. Hence if I A current flows through a conductor, it implies that 6 . 25 × 10 18 electrons pass in 1 second across the cross section of the conductor. The direction of current is conventionally taken opposite to the direction of motion of electrons. If n electrons pass through a cross section of a conductor in time t, then total charge passed Q = n × e and current in conductor Instrument by which current measured: Current is measured by an instrument called ammeter.

3.2 CONDUCTION OF ELECTRICITY 1. Conductor: Substances which allow electricity to pass through them are called conductors; such as silver, gold, acidic solution, salt solution, etc. 2. Insulator: Substances which do not allow electric current to pass through them are called insulators; such as plastic, rubber, etc. 3. Good conductor and Bad Conductor: Substances which allow electric current to pass through them easily are called good conductors of electricity; such as silver, gold, aluminium, etc. Some substances allows electric current to pass through them but in very little amount. Therefore, such substances called bad conductors of electricity, rather than being called as insulator. In fact, most of the substances allow electric current to pass through them under certain conditions, so instead of using terms conductors and insulators, good conductors and bad conductors are used.

3.3 ELECTRIC CIRCUIT An electric cell or dry cell is the source of energy for the bulb to glow and warm up. Let us now learn the way in which this electric energy is made available to the bulb in the torch.

Making of a Simple Electric Circuit Step 1: Take out the bulb from bulb from a torch. Examine the bulb carefully. The bulb is a small globe of thin glass enclosing a coiled filament supported on two thick wires. One of these thick wires is connected to the metal casing around the base of the bulb. The other wire is connected to the metal tip at the base. The metal casing and the metal tip at the base are the two terminals of the bulb.

Step 2: Take two pieces of insulated wire. Insulated wires have metal wire inside with a plastic covering on the outside. Remove the plastic covering from both the ends of each piece of wire. Fix these wires on the bulb as shown in the picture with the help of Insulating adhesive tape. Or fix the bulb on a bulb holder. The two screws on the bulb holder are the two terminals which are connected to the two terminals on the bulb. The two pieces of wire be connected to the two terminals on the holder, as shown in the picture.

Step 3: Connect the two free ends of the wires from the bulb or the bulb holder to an electric cell in such a way that one piece of wire is connected to the positive terminals of the cell and the other to the negative terminal of the cell. This may be done with the help of a rubber band or an adhesive tape. When you have finished with connections, the bulb lights up. With your finger trace the path of the electricity from the positive (+ ve) terminal on the cell to the negative (–ve) terminal of the cell. It is a roundabout path travelled by electricity.

Step 4: The dry cell has two terminals. The central terminal of the dry cell is called positive terminal. The base of the dry cell (which is made of a metal) is called negative terminal. Figure shows the terminals of dry cell. The long line represents positive terminal of the cell and the small and thick line represents negative terminal of the cell.

For this experiment you need a torch cell; a torch bulb marked 1.5 V, cellotape, a plastic coated 1 metre long copper wire and an old used blade.

Cut the plastic coated copper wire into two halves A and B. Remove plastic coating from each end of the wire such that 1 cm of plastic is removed. Now fix one bare end of each wire A and B to the terminals of 1.5 V bulb with the cellotape. Fix the other end of wire A to the base of cell with the help of cellotape. Now touch the bare end of wire B to the central terminal of cell as shown in figure. What do you observe? The bulb lights up. This shows that electric current is flowing in wire A and B through the bulb. The path along which electric current flows is called electric circuit. Now remove the wire B from the central terminal as shown in Fig. . What do you observe? The bulb does not glow. It is because electric current does not flow, if the path is broken or path is incomplete.

Closed Circuit or Complete Circuit

When the path which starts from one terminal of the cell, ends at the other terminal of the cell, without any break, then such a circuit is called complete circuit or closed circuit. When the circuit is closed, then any electric  appliance in that circuit starts working. In the present case the bulb starts glowing. Open Circuit or Incomplete Circuit When the path of current, starting from one terminal of the cell to another terminal of the cell is broken or incomplete, then such a circuit is called open circuit or incomplete circuit. For example, when we remove wire B from central terminal of cell, then the circuit is open circuit or incomplete circuit. Switches are used in the household wiring^ to open or close the electric circuit. When we switch on a particular electric appliance, we close the electric circuit. Conversely, when we switch off an electric appliance, we open the electric circuit. Symbols used in Electrical circuits: You find hereunder some symbols used in electrical circuits.

A switch, a simple device to ‘close’ or ‘open’ a circuit: An electric circuit passes through a switch. Switch is a simple device which helps us to close or open the circuit. It helps in saving electricity when not in use. You are always advised to switch ‘off the lights or other gadgets in your home to save electricity.

Connecting Electric Cells in Series Take a dry cell and a torch bulb. Connect the bulb to the cell using copper wires as shown in Fig. . Observe the intensity- of light. The bulb does not glow brightly.

Now take one more dry-cell and connect two cells as shown in figure. In this method the positive of the first cell is connected to the negative of the second. The negative of the first and the positive of the second are connected to the bulb. The bulb now glows brighter. In the battery torch or battery light two or three dry cells are put into a metal container in series. The positive of one cell is connected to the negative pole of another cell in the series connection, When the, switch is turned on, the circuit is closed and the bulb glows and gives light.

Connecting Electric Cells in Parallel Connect one torch bulb to one cell as you did in fig. You, will observe that, the bulb toes not glow brightly.

Take three dry cells and connect them as shown in fig.. That is all the positive poles of the three cells are connected together, and all the three negative poles are connected together. These three positives and three negatives are connected to the bulb- You will observe that there is no change in the brightness of the bulb! When cells are connected in parallel, their total electromotive force is the same as that if any one of them. When cells are connected in series, their electromotive force is equal to the sum of the EMF of all the cells used. Connect three torch bulbs in series as shown in figure. Connect this to a dry cell and observe that brightness of each of the three bulbs. Now connect one more dry cell in series with he first cell. Observe the brightness of each of the bulb. Then connect one more dry cell in series with the first two cells. Again observe the bulbs.

Disconnect one of the three bulbs in the circuit. The circuit becomes open and all the three bulbs stop glowing. In series connection of bulbs,’ if one bulb gets fused, all the other bulbs in the series will stop working. Three bulbs connected in Series

Connecting Bulbs in Parallel Connect three bulbs in parallel. That is, one end of each of the three bulbs are connected one wire, the other ends of the three bulbs are con nected to another wire! These two wires are connected to a dry cell. All the three bulbs glow dimly. Now disconnect one of the bulbs. The other bulbscontinue to glow as before.

To study the properties of (i) Series circuit, (ii) Parallel circuit Materials required : a battery of four cells two bulbs of 1 watt each one fused bulb a switch few lengths of connecting wires cellotape.

Method: Connect the bulbs A and B in series by connecting them to connecting wires with the help of cellotape as shown in Fig.(a). Connect the free ends of connecting wires to a battery through a switch. Close the switch. What do you observe? Both the bulbs will glow*. However, they will not glow very brightly. Open the switch. What do you observe?

Both the bulbs will stop glowing. Now remove the bulb B and instead fix a fused bulb C [Fig. ]. What is your observation? Bulb A does not glow.

Following are the conclusions from the above investigation. 1. In series circuit all the appliances work simultaneously when switch is closed. Conversely, all appliances stop working when switch is open. 2. In series circuit, if any, of the appliances goes out of order, the other appliances stop working. 3. As the bulbs were not glowing very brightly, it can be concluded that in series the appliances do not work to their full capacity. Now connect the bulbs A and B in parallel, such that they have common positive and common negative terminals as illustrated by Fig. , through a switch and a battery.

Close the switch. What do you observe? Both the bulbs A and B glow very brightly. Now remove the bulb B and instead fix a fused bulb C Fig. . What is your observation?

The bulb A continues glowing brightly, whereas bulb C does not glow. Following conclusions can be drawn from above investigation. 1. In parallel circuit all the appliances work independently 2. In parallel circuit if one appliance goes out of order, the other continues working. It means that each appliance in parallel circuit can be operated independently by a switch. 3. As the bulbs glow brightly, it means each appliance gets enough electric energy, and hence, works to its full capacity.

3.4 CHEMICAL EFFECTS OF ELECTRIC CURRENT The passage of an electric current through a conducting solution causes chemical reactions. This is known as the chemical effect of electric current. Some of the chemical effects of electric current are the following: • Formation of bubbles of a gas on the electrodes • Deposition of metal on electrodes • Change in colour of solutions Example (a) When electric current is passed through water, water dissociates into hydrogen and oxygen. Hydrogen is deposited over negative pole and oxygen is deposited over positive pole. Deposition of hydrogen and oxygen at different poles is visible in the form of bubbles. (b) When electric current is passed through the solution of a metal salt, such as solution of copper sulphate, metal gets deposited at the negative pole, because metal is positively charged. (c) Sometimes, the colour of solution also changes when electric current passes through it. The above examples are some of the chemical effects of electric current. The chemical reaction depends upon the type of solution through which electric current is passed.

3.5 ELECTROLYSIS • The process of decomposition of a chemical compound in a solution when an electric current passes through it is called electrolysis. • The solution that conducts electricity due to the presence of ions is called an electrolyte. • Two electrodes are inserted in the solution and are connected to the terminals of a battery with a switch in between. This arrangement is called an electrolytic cell. • The electrode that is connected to the positive terminal of the battery is called the anode, and the other connected to the negative terminal is called the cathode. • The electrolyte contains ions, which are charged. The positively charged ions are called cations and the negatively charged ions are called anions . Cations, being positively charged, get attracted to the negatively charged cathode and move towards it.

3.6 ELECTROPLATING Electroplating is one of the chemical effects of electric current. Electroplating is a chemical process using which a metal is coated with a layer of another desired metal. Electroplating is done to make the metals shiny. Electroplating is done over the articles made of iron to make the iron shiny and to prevent iron from getting rusted.

Use of electroplating (a) Water pipes, which are made of iron, are coated with a layer of zinc metal by the process of electroplating. Zinc is less reactive than iron and thus prevents the iron pipe from getting rusted. (b) Rims of wheel of cycle, cars, etc. are electroplated with chromium metal. Layer of chromium metal give them shiny appearance and prevents from rust. (c) Ornaments made of silver or other cheap metals are electroplated with gold to give them appearance like gold. (d) Tin cans used for storing food are made of iron electroplating with a coat of tin. Tin is less reactive than iron, and prevent foods packed in them from getting spoiled.

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Class 8 Science Chapter 11 Practice Question Answers - Chemical Effects of Electric Current

Q1: What are good conductors? Ans: The substances that conduct electricity through them are called good conductors. Q2: What are insulators or poor conductors? Ans:  The substances that do not conduct electricity through them are poor conductors or insulators. Q3: Give four examples of conductors. Ans:  Copper, iron, aluminium and brass. Q4: Give four examples of insulators. Ans: Air, wood, rubber and plastic. Q5: Name two metal objects which have a coating of another metal. Ans:  Handlebars of bicycles, bathroom taps. Q6: What do we get on electrolysis of acidified water? Ans: Hydrogen and oxygen gas. Q7: Is air a bad or good conductor? Ans: A bad conductor. Q8: Which metal is plated on handle bars of cycles and rim of wheels? Ans:  Chromium Q9: Substances that conduct electricity are called ___________. Ans:  conductors Q10: Substances that do not conduct electricity are called ___________. Ans: insulator Q11: A cation has ___________ charge. Ans: positive Q12: Some liquids are ___________ conductors of electricity and some are ___________ conductors of electricity. Ans: good, poor Q13: Distilled water is an ___________. Ans:  insulator Q14: Which of the following is a bad conductor of electricity? (a) Distilled water (b) Silver nitrate (c) Sulphuric acid (d) Copper sulphate Ans:  (a) Explanation: Distilled water is a poor conductor of electricity. This is because it contains very few ions or charged particles that can carry an electric current. Pure water has a very low concentration of ions, making it a non-conductor or insulator. Q15: Which of the following does not conduct electricity? (a) Sugar solution (b) Vinegar solution (c) Lemon juice solution (d) Caustic soda solution Ans: (a) Explanation:  Sugar solution does not conduct electricity. Like distilled water, sugar solution does not have sufficient ions to allow the flow of electric current. Substances that do not conduct electricity are called insulators. Q16: An electric current can produce (a) heating effect (b) chemical effect (c) magnetic effect (d) all of these Ans:  (d) Explanation: An electric current can produce multiple effects: a heating effect (as seen in electric stoves or heaters), a chemical effect (electrolysis, where chemical reactions occur at the electrodes), and a magnetic effect (which results in the creation of a magnetic field around a current-carrying wire). Q17: Pure or distilled water is a (a) poor conductor (b) good conductor (c) both (a) and (b) (d) none of these Ans:  (a) Explanation: Pure or distilled water is a poor conductor of electricity due to its low ion concentration. While it can become conductive if impurities are dissolved in it, the pure form of water is considered a non-conductor. Q18: Which of the following is a good conductor? (a) Brick (b) Steel (c) Plastic (d) Cotton Ans: (b) Explanation: Steel is a good conductor of electricity. Metals, in general, are good conductors because they have mobile electrons that can move freely within the material, allowing the flow of electric current. Steel is a metal and, therefore, a good conductor. Value-Based Questions

Q19: Yakub made an circuit as shown in the figure. He observed that the bulb did not glow but on bringing a compass needle near it shows deflection. He was quite confused that if current is flowing through the circuit then why the bulb is not glowing. Meanwhile his friend Sourav arrived and suggested him to add one more cell in the circuit. The bulb, then started glowing.

• Define a circuit.
• What does the deflection of a compass needle shows?
• Why the bulb did not glow in the first case but glow in the second case?
• What value of Sourav is shown here?
• Circuit is a closed path through which an electric current flows.
• Deflection of compass needle shows that the current is flowing in the circuit. It is magnetic effect of current.
• The current flowing through the circuit in first case was too low to make the bulb glow but on adding a cell in the second case makes the bulb glow.
• Sourav is an intelligent, helpful, analytical and with scientific aptitude.

Q20: While demonstrating an experiment to show whether the given liquid conduct electricity or not to class VIII students, teacher reminded everybody that one should not conduct experiment with the electric supply from the mains or a generator or an inverter. They should use electric cells for the activity.

• Do liquids conduct electricity?
• Why we should not use electric source from mains generator or an inverter?
• What values do we get from this?
• Yes, liquids which are solutions of acids, bases and salts conduct electricity. Other liquids such as oil, alcohol, sugar solution and pure water do not conduct electricity.
• Current flowing from mains, generator or an inverter is very large. So to avoid the chances of elec-trocution and short-circuit we must use cells for experiments.
• We get awareness of not using main electric supply and precaution to be followed while doing experiment.

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Chemical Effects of Electric Current Class 8 MCQ Test (Online Available)

Free mcq test, table of content, chemical effects of electric current test - 16.

Duration: 10 Mins

Maximum Marks: 10

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Lakhmir Singh Science Class 8 Solutions Chapter 14 Chemical Effects of Electric Current

Table of Contents

S Chand Science Class 8 Solutions Chapter 14 Chemical Effects of Electric Current

Lakhmir singh science class 8 chapter 14 very short answer type questions.

Question 1. Do liquids also conduct electricity? Answer: Liquids do conduct electricity, when they have free ions available like in case of Acids, Bases and Salts being dissolved in water.

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Question 2. Name two liquids which conduct electricity and two liquids which do not conduct electricity. Answer: Tap water and lemon water conduct electricity, this happens because tap water. while distilled water and wine do not conduct electricity.

Question 3. Name a device which glows even when a weak electric current passes through it. Answer: A Light Emitting Diode (LED) glows even when a weak electric current passes through it.

Question 4. Write the full form of LED. Answer: Light emitting Diode (LED)

Question 5. How would you classify lemon juice- a good conductor or a poor conductor of electricity? Answer: Lemon juice is a good conductor of electricity. Lemon is a citrus fruit containing citric acid. Acids give H+ ions when dissolved in water, these free cations and anions make lemon juice a good conductor.

Question 6. Vinegar is a sour liquid. State whether vinegar will conduct electricity or not. Answer: Vinegar is a poor conductor of electricity because it does not have any free ions to carry electric charge and conduct electricity.

Question 7. What effect does an electric current produce when flowing through a conducting liquid (or conducting solution)? Answer: When electric current passes through a conducting liquid, it gets decomposed into ions. The conducting solution has free ions available which conduct electricity.

Question 8. When electric current is passed through acidified water, then hydrogen and oxygen are formed. What type of effect of current is illustrated by this statement? Answer: When electric current is passed through acidified water, it dissociates water into H + and OH – ions. This process is called chemical effect.

Question 9. Acidified water is electrolyzed by using carbon electrodes. What is produced at: (a) positive carbon electrode? (b) negative carbon electrode? Answer: (a) Oxygen Gas is produced at positive carbon electrode. (b) Hydrogen gas is produced as negative carbon electrode.

Question 10. Give one example of the chemical effect of electric current. Answer: When an electric current is passed through a conducting solution, then chemical reactions take place in the solution. These chemical reactions cause chemical effects in the solution. Example: When an electric current is passed through water, then water dissociates into hydrogen and oxygen. The chemical reaction is shown below: H 2 O → H + (aq) + OH – (aq)

Question 11. What should be done to decompose water into hydrogen and oxygen? Answer: Electric current must be passed through water to decompose water into hydrogen and oxygen.

Question 12. Name the process in which a coating of one metal can be deposited on the surface of another metal by using current from a battery. Answer: Electroplating is the process in which a coating of one metal can be deposited on the surface of another metal by using current from a battery. The metal that needs to be deposited is used as the cathode while the metal on which it is deposited is used as anode. We use the salt of the cathode as the electrolyte.

Question 13. Name the metal which is usually electroplated on car parts such as bumpers and bicycle handlebars made of steel. Answer: Chromium is electroplated on car parts such as bumpers and bicycle handlebars made of steel.

Question 14. Which metal is electroplated on iron for making ‘cans’ used for storing food? Answer: Tin is electroplated on iron for making ‘cans’ used for storing food.

Question 15. Name two metal objects which have a coating of another metal. Answer:

• Chromium is electroplated on other metals.
• Gold is electroplated on other cheap metals.

Question 16. Name the most common application of the chemical effect of electric current. Answer: The two most common examples of the chemical effect of electric current are:

• Gold Coating on cheap metals
• Electroplating of chromium metal to avoid corrosion.

Question 17. Name two metals which are usually electroplated on cheaper metals for making jewelry (or ornaments). Answer: Gold and silver are electroplated on cheaper metals for making jewelry or ornaments.

Question 18. Which is the polluting waste generated by electroplating factories? Answer: The conducting solution used in the electroplating process is the waste generated by electroplating factories.

Question 19. Give a list of five objects around you which are electroplated. Answer: The list of five objects around you which are electroplated is:

• Kitchen utensils.

Question 20. Name two metals which are purified by using the chemical effect of current (or electrolysis). Answer: Copper and Gold are purified by using the chemical effect of current (or electrolysis).

Question 21. Name two metals which are produced (or extracted) by using the chemical effect of electric current. Answer: Carbon and hydrogen are extracted by using the chemical effect of electric current.

Question 22. Name one chemical compound which is produced by using the chemical effect of electric current. Answer: Copper sulphate is one chemical compound which is produced by using the chemical effect of electric current.

Question 23. Name one compound which is decomposed into hydrogen and oxygen by using the chemical effect of electric current. Answer: Water is one compound which is decomposed into hydrogen and oxygen by using the chemical effect of electric current.

Question 24. State whether the following statements are true or false : (a) Rainwater is a non-conductor of electricity. (b) A piece of fresh potato does not conduct electricity at all. Answer: (a) False. Rainwater is a conductor of electricity because it has dissolved ions that conduct electricity. (b) False. A piece of fresh potato conduct electricity at all because it does not have ions to conduct electricity.

Question 25. Fill in the following blanks with suitable words: (a) Most liquids that conduct electricity are solutions of ……….., ……… and ………… (b) LED glows even when a …………..electric current passes through it. (c) The passage of an electric current through a conducting solution causes………….effect. (d) When electric current is passed through acidified water, then ……..and………..are formed. (e) The process of depositing a layer of any desired metal on another metal by means of electricity is called ………. (f) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the …………terminal of the battery. Answer: (a) Most liquids that conduct electricity are solutions of acids, base and salts. (b) LED glows even when a low electric current passes through it. (c) The passage of an electric current through a conducting solution causes chemical effect. (d) When electric current is passed through acidified water, then hydrogen and oxygen are formed. (e) The process of depositing a layer of any desired metal on another metal by means of electricity is called electroplating. (f) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery.

Lakhmir Singh Science Class 8 Chapter 14 Short Answer Type Questions

Question 26. Which of the following liquids conduct electricity and which do not conduct electricity? Lemon juice, Milk, Vinegar, Common salt solution, Sulphuric acid solution, Sugar solution, Distilled water, Honey, Sea water, Rainwater. Answer: Lemon juice, Milk, Vinegar, common salt solution, Sulphuric acid solution, Sea water, and Rainwater conduct electricity.

Sugar solution, Distilled water and Honey do not conduct electricity.

Question 27. Why is it dangerous to touch a working electrical appliance with wet hands? Answer: Because wet hands have water and water is a good conductor of electricity. A person can get electric shock if he touches any electrical appliances with wet hands.

Question 28. What is the advantage of using LED in testing the electrical conductivity of liquids ? Answer: The advantage of using LEDs is because, they glow up even if very small amount of current passes through them.

Question 29. Which effect of electric current is utilized for detecting the flow of current through a solution: (a) when a torch bulb is used? (b) when a compass is used? Answer: (a) Heating effect of current is used detecting the flow of current through a solution.

(b) Magnetic effect of current is used detecting the flow of current through a solution.

Question 30. What happens to the needle of a compass kept nearby when electric current is switched on in a wire? Why does this happen? Answer: The current carrying wire behaves like a magnet and it will cause deflection of the needle of the compass. This is called magnetic effect of electric current.

Question 31. Explain why, distilled water does not conduct electricity but tap water conducts some electricity. Answer: Distilled water does not conduct electricity because it does not contain any ions which make it conducting. But it can conduct electricity when a pinch of common salt is added to it, as salt solution is conducting in nature.

Question 32. Distilled water does not conduct electricity. What substances can be added to distilled .water in small amounts to make it a good conductor of electricity? Why? Answer: Lemon solution, salt, vinegar, sulphuric acid etc. can be added to added to distilled .water in small amounts to make it a good conductor of electricity. Because distilled water does not contain any ions which make it conducting. But adding these will provide free ions for conducting solution.

Question 33. Which of the two is a better conductor of electricity: drinking water (tap water) or sea water? Give reason for your answer. Answer: Sea water is a better conductor because it contains sodium and chloride ions in large amounts. These ions make the solution conducting and thus, sea water is considered better conductor than the tap water which does not contain ions in large amounts.

Question 34. Why does a brand new bicycle have shining handlebar and wheel rims? What will happen if these are accidentaly scratched? Answer: The shining coating is done on the metal by electroplating. When these are accidentaly scratched then, the metal will be rusted due to presence of air. So, by some metal these are coated so as to avoid rusting of iron mainly used to build the handlebars and wheel rims.

Question 35. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain. Answer: No, it is very risky and unsafe for the electrician to carry out electrical repairs outdoors during heavy downpour because rain water is conducting in nature as it contains dissolved salts. The electrician may get electrical shocks while working outdoors during rain as water may conduct electricity.

Question 36. When the free ends of a conductivity tester (made by using a battery connected to a wire wound around a compass) are dipped into a solution, the magnetic needle shows deflection. Can you give the reason for this deflection. Answer: Because the free ends of a conductivity tester are dipped into a conducting solution then, it behaves like a current carrying wire and a current carrying wire behaves as a magnet because it produces magnetic field around it. And, due to this there is deflection in the compass.

Question 37. A beaker contains an acidified copper sulphate solution. A copper plate and a carbon rod are kept in this copper sulphate solution. The copper plate is connected to the positive terminal of a battery whereas the carbon rod is connected to the negative terminal of the battery. What will you observe when an electric current is passed through this set-up for a considerable time? Answer: The carbon is a non-metal which is more reactive than copper. When, an electric current is passed through this set-up for a considerable time, then carbon replaces copper ions from solutions and they deposit on the negative electrode. Thus, a red-brown layer of copper metal will be deposited on the carbon rod connected to the negative terminal of the battery.

Question 38. Does pure water conduct electricity? If not, what can we do to make it conducting? Answer: No. Pure water does not conduct electricity. Pure water does not contain any ions which make it conducting. But it can conduct electricity when a pinch of common salt is added to it, as salt solution is conducting in nature.

Question 39. In case of a fire, before the firemen use the water hoses to throw water to douse fire, they shut off the electricity supply for the area. Explain why this is done. Answer: In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area because water may conduct electricity. If the electrical supply for the area is not shut off and water is poured over electrical appliances, then electricity may pass through water and harm the firemen.

Question 40 A. Which effect of electric current is utilized when a thin layer of chromium metal is deposited on an iron tap? What is this process known as? Answer: This is called chemical effect of heating and the process is called as electroplating.

Question 40 B. For electroplating copper on an iron object, which terminal of the battery (positive or negative) is connected to the iron object? Also name the electrolyte you will use for this purpose. Answer: In the process of electroplating, the metal to be electroplated is taken as cathode and the one used for coating is chosen as the anode. And, we know, anode is positive terminal and the cathode is negative terminal. Thus, negative terminal will be connected to the iron object.

Lakhmir Singh Science Class 8 Chapter 14 Long Answer Type Questions

Question 41 A. What is meant by the chemical effect of electric current? Explain with the help of an example. Answer: When electric current passes through any conducting solution, then chemical reactions take place inside the conducting solution. This effect is called as chemical effect of electric current. Example, electroplating. The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.

Question 41 B. Name any two applications of the chemical effect of electric current. Answer:

• Chromium plating is done on metals body parts of cars, bikes, cycles, etc.
• Gold and silver plating is done on the artificial jewelry.

Question 41 C. What is electrolysis? Explain why, in the electrolysis of water, ‘acidified water’ is used. Answer: Electrolysis is the process of dissociation of water molecules into H + and OH – ions. When electric current Is passed through it in a conducting state. Because water does not have much higher concentration of ions. Dilute sulphuric acid is added to increase the concentration of ions in the water.

Question 42 A. Name three types of substances in which an electric current can produce a chemical effect. Answer: The three types of substances in which an electric current can produce a chemical effect.

• Copper sulphate

Question 42 B. State some of the characteristics of chemical changes brought about by the chemical effect of electric current. Answer: The some of the characteristics of chemical changes brought about by the chemical effect of electric current:

• The solution colour changes might take place.
• The bubbles evolve through the solution.
• The chemical deposition of one metal and replacement of the other metal.

Question 42 C. Why does an electric bulb glow when a current passes through it? Answer: The electric bulb glows because it completes the circuit when put in the conducting solution and the conducting solution helps to glow the bulb.

Question 43 A. What is meant by electroplating? What is the purpose of electroplating? Answer: The process of coating of a layer of any metal over other metal is called electroplating. The purpose of electroplating is to provide the shiny appearance, rust free metal surface etc.

Example 1. Chromium plating is done on metals body parts of cars, bikes, cycles, etc. 2. Gold and silver plating is done on the artificial jewelry.

Question 43 B. Which properties of chromium metal make it suitable for electroplating it on car bumpers, bath taps and bicycle handlebars, etc., made of iron? Answer: The chromium metal is suitable for electroplating it on car bumpers, bath taps and bicycle handlebars, etc., made of iron because it is corrosion resistant and also gives shiny appearance.

Lakhmir Singh Science Class 8 Chapter 14 Multiple Choice Questions (MCQs)

Question 46. In an activity to check the conduction of electricity through two liquids labelled A and B by using a bulb, it is observed that the bulb glows brightly for liquid A while it glows very dimly for liquid B. A. Liquid A is a better conductor than liquid B B. Liquid B is a better conductor than liquid A C. Both liquids are equally conducting D. Conducting properties of liquids cannot be compared in this manner Answer: A. Liquid A is a better conductor than liquid B Because current flows more easily throughout liquid A than B. Thus, A is a better conductor than liquid B.

Question 47. Which of the following does not conduct electricity? A. Vinegar solution B. Sugar solution C. Lemon juice solution D. Caustic soda solution Answer: B. Sugar solution Sugar solution does not contain any ions. Thus, it does not conduct electricity.

Question 48. Which of the following metals should be electroplated on a tiffin box made of steel? A. copper B. chromium C. silver D. tin Answer: D. tin Tin should be electroplated on a tiffin box made of steel as it is non-corrosive.

Question 49. Which of the following metals are produced by the electrolysis of their molten compounds? A) Copper B) Silver C) Aluminium D) Sodium A. A and B B. Band C C. C and D D. only D Answer: C. C and D Both Aluminum and Sodium metals are produced by the electrolysis of their molten compounds because they are not freely available. They need to be extracted from their sources.

Question 50. Which of the following types of energy can be used to decompose water into its elements? A. heat energy B. light energy C. chemical energy D. electrical energy Answer: D. electrical energy Electrical energy is used to decompose water into its elements i.e. hydroxide (OH – ) and (H + ) ions.

Question 51. Which of the following compounds is manufactured by using the chemical effect of electric current? A. ammonium hydroxide B. sodium carbonate C. magnesium hydroxide D. sodium hydroxide Answer: D. sodium hydroxide Sodium hydroxide (NaOH) is manufactured by using the chemical effect of electric current when a sodium salt is electrolysed.

Question 52. Which of the following objects should not be chrome-plated ? A. car bumper B. gas stove C. frying pan D. bicycle bell Answer: C. frying pan Frying pan should not be chrome-plated because it can enter the body by mixing in the food which can prove to be dangerous for the body.

Question 53. Which of the following is a weak electrolyte? A. carbonic acid B. sodium hydroxide C. copper sulphate D. nitric acid Answer: A. carbonic acid Carbonic acid is a weak electrolyte because it does not completely dissociate into the aqueous solution.

Question 54. Electrolytes conduct electricity due to the movement of: A. electrodes B. atoms C. electrons D. ions Answer: D. ions Electrolytes conduct electricity due to the movement of ions. Because positive and negative ions conduct electricity.

Question 55. Non-metals are generally non-conductors of electricity. The non-metal whose one of the forms can be used to make electrodes in electrolysis experiments is: A. iodine B. carbon C. silicon D. phosphorus Answer: B. carbon The non-metal whose one of the forms can be used to make electrodes in electrolysis experiments is Carbon and the form is graphite form. We come across graphite electrodes because it is a good conductor.

Question 56. The decomposition produced by passing current through a conducting liquid is called: A. dialysis B. hydrolysis C. electrolysis D. electroplating Answer: C. electrolysis Electrolysis is the decomposition produced by passing current through a conducting liquid. The solution is dissociated into ions.

Question 57. Which of the following is not an application of the chemical effect of electric current? A. electroplating of metals B. purification of metals C. decomposition of elements D. decomposition of compounds Answer: C. decomposition of elements Decomposition of elements is not an application of the chemical effect of electric current. Electroplating, purification and decomposition of compounds can be done with the help of chemical effect of electric current.

Question 58. One of the following is not used for electroplating metal articles. This one is : A. nickel B. chromium C. sodium D. silver Answer: C. sodium Sodium is not used for electroplating metal articles. Because it is a corrosive metal.

Question 59. An arrangement having two carbon rods kept in a conducting liquid in a vessel is known as: A. rechargeable cell B. storage cell C. biological cell D. electrolytic cell Answer: D. electrolytic cell An electrolytic cell is an arrangement having two carbon rods kept in a conducting liquid in a vessel. This is the process setup for the electrolysis of electrolytes.

Question 60. Which of the following effects is not produced by the chemical reactions brought about by an electric current? A. bubbles of gases on electrodes B. deposits of metals on electrodes C. change in color of solution D. formation of a precipitate Answer: D. formation of a precipitate Formation of a precipitate is not produced by the chemical reactions brought about by an electric current. Because it does not involves any chemical reaction but involves chemical changes in the solutions

Question 61. Which of the following can be electroplated with chromium? A) Bakelite B) Graphite C) Steel D) Teflon A. A and B B. B and C C. only C D. B and D Answer: B. B and C Graphite and Steel can be electroplated with chromium. Chrome plating is not done on graphite and steel electrodes.

Question 62. In order to obtain a coating of silver metal on a flower vase made of copper, the electrolyte has to be: A. silver nitrate solution B. copper nitrate solution C. sodium nitrate solution D. copper sulphate solution Answer: A. silver nitrate solution In order to obtain a coating of silver metal on a flower vase made of copper, the electrolyte has to be silver nitrate solution. Because the silver ions will come from the electrolyte.

Question 63. The process of purification of an impure metal is like: A. electroplating a metal on the same type of metal B. electroplating a metal on another type of metal C. producing a chemical compound by electrolysis D. decomposing a chemical compound by electrolysis. Answer: A. electroplating a metal on the same type of metal The process of purification of an impure metal is like electroplating a metal on the same type of metal. The pure metal is removed and deposited on the pure metal.

Question 64. The device which can be used to detect very small current flowing in an electric circuit is: A. LEAD B. dB C. MCB D. LED Answer: D. LED LED Light emitting diode is used to detect very small current flowing in an electric circuit.

Question 65. If plus sign (+) denotes the positive electrode and minus sign (-) denotes the negative electrode, then which of the following statement is correct for an iron spoon to be copper-plated ? A. Iron spoon (+),copper plate(-), Iron sulphate electrolyte B. Iron spoon(-), copper plate(+), Iron sulphate electrolyte C. Copper plate(-), Iron spoon(+), Copper sulphate electrolyte D. Copper plate(+), Iron spoon(-), Copper sulphate electrolyte Answer: D. Copper plate(+), Iron spoon(-), Copper sulphate electrolyte Copper plate(+), Iron spoon(-), Copper sulphate electrolyte is the correct setup combination for electroplating. Because the anode is made the metal to be deposited and cathode to the one on which it is electroplated.

Lakhmir Singh Science Class 8 Chapter 14 Questions Based On High Order Thinking Skills (HOTS)

Question 66. A student staying in a coastal region tests the drinking water and also the sea water ‘With a circuit in which a part of the connecting wire is wound around a matchbox containing compass. He finds that the compass needle deflects more in the case of sea water. Can you explain the reason? Answer: Sea water is a better conductor because it contains sodium and chloride ions in large amounts. These ions make the solution conducting and thus, sea water is considered better conductor than the drinking water which does not contain ions. The ions of drinking water are removed while removed while purifying it.

Question 67. When an electric current is passed through a cut potato for a considerable time, a coloured spot is formed around one of the electrodes : (a) What is the colour of the spot? (b) Around which electrode (positive or negative electrode) the coloured spot is formed? (c) Which effect of electric current is involved in this case? Answer: (a) The spot color is Greenish blue.

(b) The coloured spot is formed around the positive electrode.

(c) This is known as Chemical effect.

Question 68. In the process of purification of copper metal, a thin plate of pure copper and a thick rod of impure copper are used as electrodes, and a metal salt solution is used as an electrolyte: (a) Which electrode is connected to the positive terminal of the battery? (b) Which electrode is connected to the negative terminal of the battery? (c) Which metal salt solution is taken as electrolyte? Answer: (a) Thick rod of impure copper is connected to the positive terminal of the battery.

(b) Thin plate of pure copper is connected to the negative terminal of the battery.

(c) Copper sulphate solution is taken as electrolyte.

Question 69. A student had heard that rainwater is as good as distilled water. So, he collected some rainwater in a clean glass beaker and tested it. To his surprise he found that the compass needle showed deflection. What could be the reason? Answer: Rain water can collect salts from the atmosphere has some dissolved salts whereas the distilled water does not. Thus, the rainwater showed the deflection because it conducts electricity.

Question 70. Name three liquids which when tested in the manner shown in figure given along side may cause the magnetic needle of compass to deflect. Answer: The Liquids that conduct electricity will cause the magnetic needle to deflect because the electric current is capable of producing magnetic effect. The liquids like lemon juice, salt water and vegetable oil allow electricity to pass through them. Hence, these liquids can be used as in the beaker to show the given effect.

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Chemical Effects of Electric Current Class 8 Extra Questions and Answers Science Chapter 14

September 7, 2020 by Prasanna

In this page, we are providing Chemical Effects of Electric Current Class 8 Extra Questions and Answers Science Chapter 14 pdf download. NCERT Extra Questions for Class 8 Science Chapter 14 Chemical Effects of Electric Current with Answers will help to score more marks in your CBSE Board Exams.

Class 8 Science Chapter 14 Extra Questions and Answers Chemical Effects of Electric Current

Extra Questions for Class 8 Science Chapter 14 Chemical Effects of Electric Current with Answers Solutions

Chemical Effects of Electric Current Class 8 Extra Questions Very Short Answer Type

Question 1. What are good conductors? Answer: The substances that conduct electricity through them are called good conductors.

Question 2. What are insulators or poor conductors? Answer: The substances that do not conduct electricity through them are poor conductors or insulators.

Question 3. Give four examples of conductors. Answer: Copper, iron, aluminium and brass.

Question 4. Give four examples of insulators. Answer: Air, wood, rubber and plastic.

Question 5. Name two metal objects which have a coating of another metal. Answer: Handlebars of bicycles, bathroom taps.

Question 6. What do we get on electrolysis of acidified water? Answer: Hydrogen and oxygen gas.

Question 7. Is air a bad or good conductor? Answer: A bad conductor.

Question 8. Which metal is plated on handle bars of cycles and rim of wheels? Answer: Chromium

Question 9. What is the full form of LED? Answer: Light Emitting Diode.

Question 10. How do we check the electric current? Answer: We check the electric current by using a tester.

Question 11. Which part of an atom is responsible for flow of current? Answer: Electron

Question 12. Why do most liquids conduct electricity? Answer: Due to the presence of ions in them, most liquids conduct electricity.

Question 13. An LED is more efficient device than a bulb. Why? Answer: LED is more efficient because it can glow even when a weak or less current flows through it.

Question 14. Do lemon juice or vinegar conduct electricity? Answer: Yes, they conduct electricity.

Question 15. How is conductivity of liquids tested? Answer: By using a tester.

Question 16. Is water from taps, handpumps, wells and ponds a good conductor? Answer: Yes, water from these sources is a good conductor.

Question 17. What makes distilled water a good conductor? Answer: Salts when mixed with distilled water make it a good conductor.

Question 18. Why is a layer of zinc coated over iron? Answer: To prevent iron from corrosion and rust.

Question 19. Will the solution of sugar in distilled water conduct electricity? Answer: No

Question 20. Why is tin electroplated on iron to make cans used for storing food? Answer: Tin is less reactive than iron. Tin coating prevents food from coming in contact with iron and thus pre¬vents it from getting spoiled or corroded.

Question 21. Why we ifse chromium electroplating on taps and bars of bicycle instead of silver and gold? Answer: Silver and gold are very expensive comparatively to chromium.

Question 22. What type of effect of current do the deposits of metal on electrodes show? Answer: Chemical effect

Question 23. What effect of current does electroplating show? Answer: Chemical effect

Question 24. Which effect of current causes the bulb to glow? Answer: Heating effect

Question 25. Which part of the bulb glows? Answer: Filament

Question 26. Name the three effects of electric current. Answer: Heating, magnetic and chemical effect.

Question 27. How can the magnetic effect of current be checked? Answer: By using magnetic compass.

Question 28. What do we see when the compass needle is brought near a wire in which current is flowing? Answer: The needle deflects.

Question 29. What is electroplating? Answer: Deposition of thin layer of a metal over other metal by electrolysis is called electroplating.

Chemical Effects of Electric Current Class 8 Extra Questions Short Answer Type

Question 1. Define good conductors and poor conductors or insulators. Answer: The materials that conduct electricity through them are called good conductors whereas those that do not conduct electricity are called poor conductors or insulators. For example, copper, brass, aluminium, iron, etc., are conductors whereas rubber, plastic, wood, air, etc., are insulators.

Question 2. How is the conductivity of liquids tested? Answer: The free ends of the tester is dipped in the liquid. If the bulb glows, the liquid is said to be a conductor. If not, it is an insulator.

Question 4. What is an LED? Why is it preferred to other type of bulbs? Answer: The electric device which is used in the tester instead of bulb is an LED. Its full form is Light Emitting Diode. It is preferred to other bulbs as it can glow even when weak or less current flows through it.

Question 5. Explain the conductivity of water. or Normal water conducts electricity while the pure or distilled water does not. Explain why? Answer: Normal water that we get from sources such as taps, handpumps, wells, ponds, etc., is not pure. It may contain several salts dissolved in it naturally. This water is thus good conductor of electricity. The pure or distilled water is free of salts and is a poor conductor.

Question 6. Give an example of chemical effect of the electric current. Answer: The passage of an electric current through a conducting solution causes chemical reactions as a result, bubbles of a gas are formed, or deposits of metal are seen on electrodes or changes in colour of solution , may occur. These are some of the chemical effects of electric current.

Question 7. What is electroplating? What are its uses? Answer: The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. Electroplating is a very useful process. This is used to make objects appear shiny and resistant to scratches. It prevents corrosion.

Question 8. What happens when electric current is passed through the copper sulphate solution? Answer: When electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it.

Question 9. How does a bulb glow in liquid? Explain. Answer: When the liquid between the two ends of a tester allows the electric current to pass through it, then the circuit of the tester becomes complete and the current flows in the circuit of liquid makes the bulb glow. But when the liquid does not allow the electric current to pass through it, then the circuit of the tester is incomplete and the bulb does not glow.

Question 10. What is the magnetic effect of electricity? Explain. Answer: When electric current is passed through a coil or wire, it behaves like a magnet. This is known as mag¬netic effect of current. It depends on amount of current passing through the coil or wire.

Question 11. Why is magnetic compass needed to test the conduction of electric current? Answer: Sometimes, when the current passing through a conductor is so small that filament of the bulb does not get heated up and the bulb does not glow. In this case, we need magnetic compass to test the conduction of current.

Question 12. What happens when an electric current is passed through a cut potato for a considerable time? Answer: When an electric current is passed through a cut potato for a considerable time, greenish blue spot is formed around positive electrode. The chemical effect of the electric current is involved in this process.

Question 13. Why is chromium used for electroplating? Why the objects have chromium plating are not made of chromium itself? Answer: Chromium has a shiny look. It does not get corroded and it resists scratches. Chromium is however expensive and it may not be economical to make the whole object out of it. So the object is made from a cheaper metal and only a coating of chromium is done over it.

Question 14. Which metals, except chromium, are used for electroplating other metals? Answer: Jewellery makers electroplate silver and gold on ornaments of less expensive metals. Tin cans, used for storing food, are made by electroplating tin onto iron. Tin is less reactive than iron. Hence, food is protected from getting spoilt. Iron used in bridges and automobiles is coated with zinc to protect them from corrosion and formation of rust. •

Question 15. Current does not flow in a circuit if there is a gap between the two wires. Does it indicate that air is a poor conductor of electricity? Does air never conduct electricity? Explain. Answer: Air is a poor conductor of electricity if it is dry but in certain cases like during lightning and when air is moist, air may conduct electricity.

Chemical Effects of Electric Current Class 8 Extra Questions Long Answer Type

Question 1. On what factors thickness of the electroplated items depend? Answer: Thickness of electroplated items depend upon:

• The strength of the current passing through the circuit.
• The concentration of the metal ion in the solution.
• The duration of the time the article has been in the solution.

Question 2. With the help of a suitable diagram, explain electrolytic refining of copper. Answer: To purify copper, a thin plate of pure copper and a thick rod of impure copper are used as electrodes in the acidified solution of CuS04. Pure copper is used as cathode and impure copper is used as anode. When electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it. From impure copper electrode, an equal amount of copper gets dissolved in the solution. Thus, the loss of copper from solution is restored and the process continues. The impurities are left behind at anode.

Question 4. What is electroplating? On which effect of the electric current is it based? Why is it done? Answer: The process of depositing or coating a layer of any desired metal on the surface of other material by means of electricity is called electroplating. It is one of the most common applications of chemical effects of electric current. Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of a different metal. The layer of metal deposited has some desired property, which the metal of the object lacks. For example, chromium plating is done on many objects to make them shiny and at¬tractive.

Question 5. What are the advantages and disadvantages of electroplating? Answer: Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of different metal. The advantages and disadvantages of electroplating are: Advantages:

• It protects the metals from being corroded.
• It prevents the rusting of metals.
• It makes cheap and dull metals shiny and attractive.
• It can make more reactive metals like iron less reactive.
• Chromium coating on metals give lustre to objects.

Disadvantages

• Pollutants from electroplating industries are very harmful. Some chemicals are very lethal for both human and animals.
• It is an expensive process.

Chemical Effects of Electric Current Class 8 Extra Questions HOTS

Question 1. Why electric fires are extinguished with either using C02 extinguisher or mud but not water? Answer: As water is a good conductor of electricity so it can cause electrocution. Hence, water is avoided in ex¬tinguishing electric fires.

Question 2. Why do you think electroplated jewelleries are in demand? Answer: Electroplated jewelleries are in demand because firstly, they are as shiny and attractive as real jewelleries. They are light-weighted and cost effective. Secondly, one feels free to wear it because of the growing problem of snatching and theft.

Question 3. Do distilled water conduct electricity? What will happen if we add sugar to it and then salt to it? Explain. Answer: No, distilled water do not conduct electricity. If we add sugar to distilled water, then also it will not conduct electricity because sugar do not dissociates into ions. But on adding salt, it will conduct electricity because aqueous salt solution is a good conductor of electricity.

Question 4. Suppose you want to deposit silver on an iron spoon using silver nitrate as electrolyte. Which terminal of the battery you should connect the spoon? What material should the other electrode be made of? Answer: Silver ion is positively charge, so the spoon must be connected to negative terminal to deposit silver on it. The other electrode should be made of silver.

Question 5. Why potato turns green on passing current? Around which terminal greenish patch is observed? Answer: Potato turns green due to chemical effect of current. Around positive terminal greenish patch in potato is observed.

Chemical Effects of Electric Current Class 8 Extra Questions Value Based (VBQs)

Question 1. Yakub made an circuit as shown in the figure. He observed that the bulb did not glow but on bringing a compass needle near it shows deflection. He was quite confused that if current is flowing through the circuit then why the bulb is not glowing. Meanwhile his friend Sourav arrived and suggested him to add one more cell in the circuit. The bulb, then started glowing. (a) Define a circuit. (b) What does the deflection of a compass needle shows? (c) Why the bulb did not glow in the first case but glow in the second case? (d) What value of Sourav is shown here? Answer: (a) Circuit is a closed path through which an electric current flows. (b) Deflection of compass needle shows that the current is flowing in the circuit. It is magnetic effect of current.

Question 2. While demonstrating an experiment to show whether the given liquid conduct electricity or not to class VIII students, teacher reminded everybody that one should not conduct experiment with the electric supply from the mains or a generator or an inverter. They should use electric cells for the activity. (a) Do liquids conduct electricity? (b) Why we should not use electric source from mains generator or an inverter? (c) What values do we get from this? Answer: (a) Yes, liquids which are solutions of acids, bases and salts conduct electricity. Other liquids such as oil, alcohol, sugar solution and pure water do not conduct electricity. (b) Current flowing from mains, generator or an inverter is very large. So to avoid the chances of elec-trocution and short-circuit we must use cells for experiments. (c) We get awareness of not using main electric supply and precaution to be followed while doing experiment.

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Class 8 Science MCQ Questions of Chemical Effects of Electric Current with Answers

Class 8 Science MCQ Questions of Chemical Effects of Electric Current with Answers?

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These Class 8 Science MCQ Questions of Chemical Effects of Electric Current with Answers will help understudies to go cover the whole part rapidly. By solving these questions understudies can acquire their certainty level while composing the last question paper. The MCQ Questions for class 8 gave here. It involves every one of the Questions that will assist understudies to elevate their score with point-by-point solutions. 

The significant Class 8 Science MCQ Questions of Chemicals Effects of Electric Current are made especially to help understudies and guide them in the right method of considering. In this section, the students will learn how various synthetics respond when an electric flow goes through them. Subsequent to perusing this part the Students will know which chemicals are good conductors of electricity and which one is a  poor conductor of electricity. Students are encouraged to solve Class 8 Science MCQ Questions of Chemicals Effects of Electric Current.

Practice Class 8 Science MCQ Questions chapter-wise

1. Which of the following is a bad conductor of electricity?

(a) Distilled water (b) Silver nitrate (c) Sulphuric acid (d) Copper sulphate

2. Which of the following does not conduct electricity?

(a) Sugar solution (b) Vinegar solution (c) Lemon juice solution (d) Caustic soda solution

3. An electric current can produce

(a) heating effect only. (b) chemical effect only (c) magnetic effect only (d) chemical, heating, and magnetic effects

4. Pure or distilled water is a

(a) poor conductor (b) good conductor (c) both (a) and (b) (d) none of these

5. Which of the following is a good conductor?

(a) Brick (b) Steel (c) Plastic (d) Cotton

6. Polythene is

(a) a conductor (b) an insulator (c) both (a) and (b) (d) none of these

7. Electroplating is based on

(a) heating effect of electricity (b) chemical effect of electricity (c) physical effect of electricity (d) magnetic effect of electricity

8. Copper is

(a) a good conductor (b) an insulator (c) both (a) and (b) (d) none of these

9. An electrolyte is

(a) a metal (b) a liquid that conducts current (c) a non-metal (d) none of these

10. Flow of electron is called

(a) electrolyte (b) electroplating (c) electrodes (d) electric current

11. Which is not a non-electrolyte?

(a) Glucose (b) Acetic acid (c) Urea (d) Ethanol

12. An electric lamp glows due to

(a) heating effect (b) magnetic effect (c) chemical effect (d) physical effect

13. Electroplating prevents

(a) corrosion (b) passing of current (c) dissociation (d) shining

14. Which of the following metal is used in electroplating, in order to bring a shine to the objects?

(a) Zinc (b) Chromium (c) Copper (d) Silver

15. In LEDs, the longer lead (wire) is always connected to the _______ terminal

(a) negative (b) neutral (c) positive (d) Any terminal

16. When electrodes are immersed in water and electricity passed, the bubbles formed on the positive terminal are actually _______ gas.

(a) Hydrogen (b) Carbon dioxide (c) Oxygen (d) Nitrogen

17. A coating of _________is deposited on iron to protect it from corrosion and the formation of rust

(a) copper (b) aluminum (c) Zinc (d) silver

18. When electrodes are immersed in water and electricity passed, the bubbles formed on the negative terminal is actually _______ gas.

19. Assertion: In electrolyte refining of metal, impure metal is made cathode while a strip of pure metal is used as an anode.

Reason: The pure metal gets deposited at the anode as anode mud. In electrolyte refining of metal, impure metal is made cathode while a strip of pure metal is used as an anode.

(a) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion (b) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion (c) Assertion is correct but Reason is incorrect (d) Both Assertion and Reason are incorrect

20. The cans, used for storing food, are made by electroplating ……………. on to irons

(a) chromium (b) zinc (c) tin (d) none of these

21. Adding lime water to tap water makes it:

(a) an electrolyte (b) electrolysis (c) no change occur (d) none of these

22. The negative charged ions are called:

(a) cations (b) anions (c) ions (d) none of these

23. Kerosene is:

(a) electrolyte (b) non-electrolyte (c) electrode (d) none of these

24. Priya's uncle has set up an electroplating factory near his village. He should dispose of the waste of the factory

(a) in the nearby river. (b) in the nearby pond. (c) in the nearby cornfield. (d) according to the disposal guidelines of the local authority

25. Which one of the following solutions will not conduct electricity?

(a) lemon juice (b) vinegar (c) tap water (d) vegetable oil

1.  Answer:  (a) Distilled water

Explanation:  The availability of ions is very important to conduct electricity. Distilled water is a poor conductor of electricity because it can not provide ions to conduct electricity.

2.  Answer: (a) Sugar solution

Explanation:  The ions float freely through the liquid move towards electrodes of opposite charges and conduct electricity. Sodium hydroxide, lemon juice, and vinegar can ionize when due to passage of electric current but sugar solution does not ionize due to electric current. Sugar solution is not an electrolyte.

3.  Answer: (d) chemical, heating, and magnetic effects

Explanation:  An electric current can produce a magnetic effect on a moving charge as a current carrying wire generate a magnetic field in its surrounding. Current can also produce a chemical effect like electrochemical reactions, it can also produce a heating effect as it generates heat in a resistance.

4.  Answer: (a) poor conductor

Explanation:  Pure or distilled water is a poor conductor of electricity.

5. Answer: Answer: (b) Steel

Explanation:  Most metals conduct electricity to a certain extent. Some metals are more highly conductive than others. Copper, silver, aluminum, gold, steel, and brass are common conductors of electricity. The most highly conductive metals are silver, copper, and gold.

6.  Answer: (b) an insulator

Explanation:  An electrical insulator is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Examples of insulators include glass, rubber, polythene, plastic, wood, and diamond.

7.  Answer: (b) chemical effect of electricity

Explanation:   A direct current (DC) of electricity is passed through the solution, affecting the transfer of metal ions onto the cathode. So the transfer of ions from one electrode to another is because of the heating effect of the current and thus, electroplating is based on the chemical effect of electricity.

8.  Answer: (a) a good conductor

Explanation:  Copper is commonly used as an effective conductor in household appliances and in electrical equipment in general. Because of its low cost, most wires are copper-plated.

9.  Answer: (b) a liquid that conducts current

Explanation:   An electrolyte is a  liquid or gel which contains ions and can be decomposed by electrolysis, i.e. that present in a battery. electrolyte conducts electricity by decomposing into its constituent ions.

10. Answer: (d) electric current

Explanation:  Electricity is the flow of electrons through a conductor, usually in the form of a wire, this flow is called an electric current. Breaking the atomic bond between an electron and its nucleus requires an input of energy which causes the electron to overcome the electromagnetic force constraining it and thus flow freely.

11.  Answer:  (b) Acetic acid

Explanation: Acetic acid is a weak electrolyte because its dissociation constant is small meaning there will be few ions in solution to conduct electricity.

12.  Answer: (a) heating effect

Explanation:  The electric lamp glows because of the heating effect of the electric current. There is a relation between heat generated and the amount of electric current; it is given by the Joule's effect of heat.

13.  Answer: (a) corrosion

Explanation: Electroplating is one of the most popular methods employed to achieve corrosion control. This metal coating acts as a sacrificial barrier that can slow and even prevent corrosion from forming on the underlying material, which is referred to as the substrate.

14.  Answer: (b) Chromium

Explanation:  Chromium is used in electroplating in order to bring a shine in the objects.

15.  Answer: (c) positive

Explanation:  Therefore, In an LED, the longer lead is always connected to the positive terminal of the battery and the shorter lead is connected to the negative terminal of the cell.

16.  Answer: (c) Oxygen

Explanation:  When electrodes are immersed in water and electricity passed the bubbles formed on the positive terminal is actually Oxygen gas..

17.  Answer:  (c) Zinc

Explanation:  Galvanization is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanization, in which parts are submerged in a bath of molten zinc.

18.  Answer: (a) Hydrogen

Explanation:  When electrodes are immersed in water and electricity passed the bubbles formed on the negative terminal is actually Hydrogen gas.

19.  Answer: (d) Both Assertion and Reason are incorrect

Explanation:  In the Electrolytic refining method, the impure metal is made to act as anode. A strip of  same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of same metal. The more basic metal remains in the solution and less basic ones go to the anode mud. Copper is refined using an electrolytic method, anode of impure copper and pure copper strips are taken as cathode in the acidified copper sulphate solution. Impurities from the blister copper deposit as anode mud.

20.  Answer: (c) tin

Explanation:  Tin is a non-reactive metal whereas iron is a reactive metal. If food is stored in an iron container, it might react with iron and get spoiled. Hence, tin is electroplated on iron to make cans used for storing food. Electroplating tin makes the container non-reactive and look better.

21.  Answer: (a) an electrolyte

Explanation:  The substances that can dissociate into ions in water can act as electrolytes.Lime water is . It dissociates into and ions. Therefore, they act as electrolytes.

22.  Answer: (b) anions

Explanation:   A negatively charged ion is known as an anion, as an anion is formed by the gain of one or more electrons by an atom.

23.  Answer: (b) non-electrolyte

Explanation:   Electrolytes are the ionic substances while kerosene is a covalent substance hence it is not electrolyte.

24. Answer: (d) according to the disposal guidelines of the local authority

Explanation:  Waste disposal is a major concern in the electroplating industry as it causes water pollution and releases a hazardous chemical into water bodies. Hence it should be disposed of according to guidelines of the local authority.

25.  Answer: (d) vegetable oil

Explanation:  Vegetable oil does not contain ions hence it cannot conduct electricity.

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• Chapter 14: Chemical Effects Of Electric Current

NCERT Solutions for Class 8 Science Chapter 14 Chemical Effects of Electric Current

Ncert solutions class 8 science chapter 14 – free pdf download.

* According to the CBSE Syllabus 2023-24, this chapter has been renumbered as Chapter 10.

NCERT Solutions for Class 8 Science Chapter 14 Chemical Effects of Electric Current, provide solutions for all the questions given in the NCERT Class 8 Science textbook. The set of solutions presented here is prepared by subject experts to help students in their studies. Students can practise more questions either by accessing or by downloading the NCERT Solutions for Class 8 Science for this chapter from BYJU’S website.

Download Exclusively Curated Chapter Notes for Class 8 Science Chapter – 14 Chemical Effects of Electric Current

Download most important questions for class 8 science chapter – 14 chemical effects of electric current.

Chemical Effects of Electric Current is the fundamental topic that is required to avoid difficulty in all future studies. This NCERT Solution helps students understand the topic and clear their doubts through its comprehensive answers. Students can easily practise and revise concepts by referring to these NCERT Class 8 Solutions . It saves their time by providing all the necessary concepts and solutions in a proper sequence.

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Access Answers to Science NCERT Class 8 Chapter 14 Chemical Effects of Electric Current

Exercise Questions

1. Fill in the blanks.

(a) Most liquids that conduct electricity are solutions of ______________ and ______________.

(b) The passage of an electric current through a solution causes ______________ effects.

(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the ___________terminal of the battery.

(d) The process of depositing a layer of any desired metal on another material by means of electricity is called _________.

(a) Most liquids that conduct electricity are solutions of acids, bases and salts.

(b) The passage of an electric current through a solution causes chemical effects.

(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery.

(d) The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.

2. When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

The compass needle shows a deflection, which concludes that current is flowing through the wire. The circuit becomes complete as the free ends of the tester are immersed inside the solution. So, the solution is conducting solution; hence, deflection is obtained in the compass needle.

3. Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.

I. Saltwater

II. Lemon juice

III. Vegetable oil

These liquids can be taken in a beaker to show the passage of electricity, as they will show a deflection in the magnetic needle.

4. The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.

The possibility of the bulb not glowing may be because of the following reasons:

a. The liquid may be non-conducting. In this case, the circuit is incomplete, and the current does not pass through the liquid.

b. Electric current may be weak for the circuit is made up of a material which is not a good conductor of electricity, or there is insufficient energy in the battery to generate electricity.

5. A tester is used to check the conduction of electricity through two liquids, labelled A and B. It is found that the bulb of the tester glows brightly for liquid A, while it glows very dimly for liquid B. You would conclude that

(i) liquid A is a better conductor than liquid B.

(ii) liquid B is a better conductor than liquid A.

(iii) both liquids are equally conducting.

(iv) conducting properties of liquid cannot be compared in this manner.

Liquid A is a better conductor than liquid B.

The conductivity of the solution determines the amount of current flowing through the solution. The greater the conductivity, the greater will be the quantity of current passing through the solution and the lesser the conductivity, the quantity of current passing through will be correspondingly less. So, the conductivity of liquid A is more than the conductivity of liquid B.

6. Does pure water conduct electricity? If not, what can we do to make it conduct?

Pure water does not conduct electricity, as it does not contain any type of salt. Adding a small amount of Common salt (Sodium Chloride, i.e., NaCl) will turn the water into a conducting medium.

7. In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.

In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area because water sprayed from the hose might conduct electricity which may come in contact with the electrical appliances, which increases the chance of electricity passing through the wire. This may hurt the firemen.

8. A child staying in a coastal region tests the drinking water and also seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?

The amount of dissolved salts present in the seawater is more than that of the drinking water. So, seawater will be a better conductor than drinking water. That is the reason behind the increased deflection of the needle in the seawater when compared to the drinking water.

9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpours? Explain.

No. It is not safe to repair electrical appliances outdoors during heavy downpours. Rainwater is composed of a certain percentage of dissolved salts making it conductive. This may cause electric shocks and harm the electrician while working outdoors during heavy downpours.

10. Paheli had heard that rainwater is as good as distilled water. So she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise, she found that the compass needle showed deflection. What could be the reasons?

Rainwater is composed of a certain percentage of dissolved salts making it conductive. This results in the deflection of the compass.

11. Prepare a list of objects around you that are electroplated.

Chromium plating: This is done on exterior parts of automobiles in order to obtain a shiny appearance.

Gold Plating: Silver ornaments are coated with a thin layer of gold, and the product is called Gold-plated Ornaments.

Zinc Plating: Iron used for Construction is coated with a Zinc layer in order to protect them from corrosion and rusting.

12. The process that you saw in Activity 14.7 is used for the purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from the impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?

The thick rod of the impure copper plate is to be attached to the positive terminal of the battery because when the electric current is passed through the copper sulphate solution, it gets dissociated into copper and sulphate. The free copper, being positively charged, gets drawn to the negative terminal of the battery and gets deposited on it. On the other hand, the loss of copper from the solution is regained from the impure copper rod, which is attached to the positive terminal of the battery.

Subtopics of Class 8 Science Chapter 14 Chemical Effects of Electric Current

• Do Liquids Conduct Electricity?
• Chemical Effects of Electric
• Electroplating

Class 8 is one of the crucial stages of a student’s life. Students of CBSE Class 8 will be writing national-level exams, like Science Olympiad and other scholarship tests. The NCERT Solutions, provided here for the Chapter Chemical Effects of Electric Current, will help the students to learn the concepts in an easy way. This chapter deals with the chemical effects of electric current, electroplating, good conductors, LED and conductors. The topics provided in this chapter are very important from an exam perspective.

Along with NCERT Solutions , students should practise lots of sample papers and previous years’ questions. Solving previous years’ questions and sample papers will help them to know about the different types of questions asked in the examination.

Frequently Asked Questions on NCERT Solutions for Class 8 Science Chapter 14

Prepare a list of objects around you that are electroplated from chapter 14 of ncert solutions for class 8 science., what are the topics included in chapter 14 of ncert solutions for class 8 science, explain electroplating covered in chapter 14 of ncert solutions for class 8 science..

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Class 8 Chemical Effects of Electric Cur...

Class 8 Chemical Effects of Electric Current

13 questions

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The movement of _______ constitutes an electric current

Driving force also called ____________ force is used to push the electrons that carry the charge around the circuit

Conventional current

Electric Current

Most liquids that conduct electricity are solution of acids, bases and distilled water

An electric current can bring about a _______ change

The process of breaking up of an electrolyte chemically on passing an electric current through it is called ______

Positively charged particles are called _______

copper get transferred from the ______ to the ______

anode , cathode

cathode , anode

An arrangement of an electrolyte, two electrodes and a source of current is called and __________ cell

Insoluble impurities settle down below the anode as _____ ___

Oxygen is released at the side of cathode

what allows electricity to flow through water?

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