introduction to stoichiometry assignment active

Unit 3: The Mole – Chemical Formulas, Stoichiometry, Limiting Reactant, Percent Yield

Introduction to stoichiometry of chemical reactions, outline of stoichiometry of chemical reactions.

• Writing and Balancing Chemical Equations
• Classifying Chemical Reactions
• Reaction Stoichiometry
• Reaction Yields
• Quantitative Chemical Analysis

Figure 1. Many modern rocket fuels are solid mixtures of substances combined in carefully measured amounts and ignited to yield a thrust-generating chemical reaction. (credit: modification of work by NASA)

Solid-fuel rockets are a central feature in the world’s space exploration programs, including the new Space Launch System being developed by the National Aeronautics and Space Administration (NASA) to replace the retired Space Shuttle fleet (Figure 1).

The engines of these rockets rely on carefully prepared solid mixtures of chemicals combined in precisely measured amounts. Igniting the mixture initiates a vigorous chemical reaction that rapidly generates large amounts of gaseous products. These gases are ejected from the rocket engine through its nozzle, providing the thrust needed to propel heavy payloads into space. Both the nature of this chemical reaction and the relationships between the amounts of the substances being consumed and produced by the reaction are critically important considerations that determine the success of the technology.

This chapter will describe how to symbolize chemical reactions using chemical equations, how to classify some common chemical reactions by identifying patterns of reactivity, and how to determine the quantitative relations between the amounts of substances involved in chemical reactions—that is, the reaction stoichiometry .

• Chemistry. Provided by : OpenStax College. Located at : http://openstaxcollege.org . License : CC BY: Attribution . License Terms : Download for free at https://openstaxcollege.org/textbooks/chemistry/get

Stoichiometry Guided Instructional Activities with Guide Framework

This set of three worksheets are intended to be used as collaborative "Guided Instructional Activities" (GIAs). Two students cooperate to complete the steps of a stoichiometry problem, alternately doing parts of the process as they explain what they are doing and evaluate their partner's work. These worksheets emphasize an algorothmic approach that helps students learn to think aobut the purpose of a question, organize their work, set it up so that it is easily readable and can be followed by others, and make good use of "unit analysis" (dimensional analysis). Good habits and organization are emphasized by introducing a "framework" in which students enter their work on the first two GIAs. Use of the framework is optional, and may be extended to other stoichiometry practice, or discontinued as soon as the teacher is satisfied that students are able to present their work neatly and successfully.

One worksheet is needed for each group of two students. Worksheets can be placed in sheet protectors and used from year to year.

These worksheets are part of a entire unit on teaching stoichiometry. You can access the complete lesson plans with information on their use, and links to other worksheets, labs, and activities at Stoichiometry is Easy .

These three activity worksheets guide students to complete stoichiometry problems using an algorithmic approach that emphasizes "unit analysis" (dimensional analysis) and the use of the "stoichiometri ratio" (coefficients of the relevant chemical species in the balanced chemical equation.

Each of the activity worksheets requires 40 to 55 minutes.

One copy of GIA for each group of two. Copies may be placed in sheet protectors to be used over again year to year, or the GIA may be projected using a document or overhead projector.

One "framework" for each group of two is also recommended, at least for the first two GIA activities. The frameworks are at this URL: https://www.chemedx.org/sites/www.chemedx.org/files/StoichFrameworks.pdf

The first framework has the steps for stoichiometry written into it. The second framework in the file does not have steps, so students can write the steps into the framework for themselves as they begin to learn this algorithmic method.

Most students, and many of my (now former) colleagues, find stoichiometry to be one of the most challenging topics in a first year (and yes, even a second year) chemistry class. But my students and I have always looked forward to the challenge, and the fun. Certainly, stoichiometry means diligent work, and for some it means frustration. But there is no reason it has to be dire, difficult, or drudgery.

I had vacillated over the years between using an algorithmic method, and an inquiry-based approach to teaching stoichiometry. After six years trying both methods in alternating years, I decided my students got more out of the algorithmic approach, and that in the process they learned several lessons that made the rest of their chemistry work easier. The five steps my students learned are by no means unique, but the frameworks included seem to help students better organize their work, gain an understanding of who the mathematical steps of stoichiometry relate to the chemical representation (equation), and encourage students to be more successful.

Guided Instructional Activities (GIAs) were part of the “Mastering Chemistry on the Web” (MCWeb) program, a part of the National Science Foundation Molecular Science Project ( http://www.molsci.ucla.edu ). Dr. Patrick Wegner (California State University, Fullerton) developed these POGIL-like (Process-Orineted Guided-Inquiry Learning) activities for use in preparatory and general chemistry classes. While some of the activities are, like POGIL real guided inquiry, many are simply cooperative learning activities that give students an opportunity to work toward a common goal while discussing and practicing skills of particular interest.

The usual procedure is to assign students randomly into groups of two (which change for each activity). They work at tables of two groups each. Students who have difficulty with an item are to consult their partner, then the other group at their table, and then may ask the teacher. Students should not move from group to group. The teacher circulates around the class making sure each group is on task, answering questions,  and revealing the answers a little at a time so students can confirm they are correctly doing what they were asked to do. This put students in charge of their own learning, gave some the opportunity to “teach” others, and allows the teacher more time to work with students who needed extra attention during class time in a non-threatening environment. At the same time, students police each other to make certain everyone (OK, nearly everyone) is on task.

These GIAs are part of a unit on stoichiometry. Read the entire article and find the lesson plans at: INSERT URL

See GIA in the student document below.

Make one copy of the GIA worksheeet for each group of two students (or arrange to project using overhead or document projector). Copies of the GIA may be placed in sheet protectors for use from year to year.

If desired, make one copy of the "framework" for each group of two students. Using the framework with the steps written in is suggested when having student complete the first GIA. Students can use the totally blank framework (and be instructed to write in the steps for themselves) for the second GIA. Use of the framework is optional for the third GIA.

The GIAs were written by Dr. Patrick Wegner, California State University, Fullerton, and revised by David Licata, chemistry/AP Chemistry, Pacifica High School, Garden Grove, CA (retired). The framworks were created by Mr. Licata.

HS-PS1-7 Mathematical Representations

Students who demonstrate understanding can use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

*More information about all DCI for HS-PS1 can be found at  https://www.nextgenscience.org/dci-arrangement/hs-ps1-matter-and-its-interactions and further resources at https://www.nextgenscience.org .

Assessment does not include complex chemical reactions.

Emphasis is on using mathematical ideas to communicate the proportional relationships between masses of atoms in the reactants and the products, and the translation of these relationships to the macroscopic scale using the mole as the conversion from the atomic to the macroscopic scale. Emphasis is on assessing students’ use of mathematical thinking and not on memorization and rote application of problem - solving techniques.

Introduction To Stoichiometry

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One of the most important parts of chemistry is stoichiometry . Stoichiometry is the study of the quantities of reactants and products in a chemical reaction. The word comes from the Greek words:  stoicheion  ("element") and  metron  ("measure"). Sometimes you'll see stoichiometry covered by another name: mass relations. It's a more easily pronounced way of saying the same thing.

Stoichiometry Basics

Mass relations are based on three important laws. If you keep these laws in mind, you'll be able to make valid predictions and calculations for a chemical reaction.

• Law of Conservation of Mass - mass of the products equals the mass of the reactants
• Law of Multiple Proportions - the mass of one element combines with a fixed mass of another element in a ratio of whole numbers
• Law of Constant Composition - all samples of a given chemical compound have the same elemental composition

Common Stoichiometry Concepts and Problems

The quantities in stoichiometry problems are expressed in atoms, grams, moles, and units of volume, which means you need to be comfortable with unit conversions and basic math. To work mass-mass relations, you need to know how to write and balance chemical equations. You'll need a calculator and a periodic table.

Here's information you need to understand before you start work with stoichiometry:

• How the Periodic Table Works
• What a Mole Is
• Unit Conversions (Worked Examples)
• Convert Grams To Moles (Step By Step Instructions)

A typical problem gives you an equation, asks you to balance it, and to determine the amount of reactant or product under certain conditions. For example, you may be given the following chemical equation:

2 A + 2 B → 3 C

and asked, if you have 15 grams of A, how much C can you expect from the reaction if it goes to completion? This would a be a mass-mass question. Other typical problem types are molar ratios, limiting reactant, and theoretical yield calculations.

Why Stoichiometry Is Important

You can't understand chemistry without grasping the basics of stoichiometry because it helps you predict how much of a reactant participates in a chemical reaction, how much product you'll get, and how much reactant might be left over.

Tutorials and Worked Example Problems

From here, you can explore specific stoichiometry topics:

• How To Balance Equations
• Example of Balancing an Equation
• Understanding Molar Ratios
• How To Find the Limiting Reactant
• How To Calculate Theoretical Yield

Quiz Yourself

Do you think you understand stoichiometry? Test yourself with this quick quiz .

• Stoichiometry Definition in Chemistry
• Theoretical Yield Definition in Chemistry
• Limiting Reactant Definition (Limiting Reagent)
• How to Calculate Limiting Reactant and Theoretical Yield
• 20 Practice Chemistry Tests
• Example Problem of Mass Relations in Balanced Equations
• How to Calculate Theoretical Yield of a Reaction
• Balancing Chemical Equations
• Mole Ratio: Definition and Examples
• Overview of High School Chemistry Topics
• Chemistry 101 - Introduction & Index of Topics
• How to Calculate Limiting Reactant of a Chemical Reaction
• Percent Yield Definition and Formula
• Mole Relations in Balanced Equations
• Redox Reactions: Balanced Equation Example Problem
• A List of Common General Chemistry Problems

Stoichiometry: Introduction to Stoichiometry

This chemistry lecture will help to define mole ratios and introduce molar mass as a conversion factor in solving stoichiometry problems.

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Stoichiometry

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Introduction to Stoichiometry Presentation

Stoichiometry in action: video #1 on how to solve stoichiometry problems, stoichiometry in action: video #2 on how to solve stoichiometry problems, stoichiometry in action: video #3 on how to solve stoichiometry problems, stoichiometry quiz/assessment, introduction to stoichiometry.

This lesson is full of information, practice problems, and more, all with the purpose of introducing your students to the concept of stoichiometry. From an introduction presentation to an assignment to assess your students' understanding, this lesson will help your students to gain a thorough understanding of this scientific process. Start with the presentation, then have your students watch the "Stoichiometry in Action" videos (in numerical order), then end with the assessment. Thanks, and have fun!

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9.1: Introduction to Stoichiometry of Chemical Reactions

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Outline of Stoichiometry of Chemical Reactions

• Writing and Balancing Chemical Equations
• Reaction Stoichiometry
• Reaction Yields
• Quantitative Chemical Analysis

Solid-fuel rockets are a central feature in the world’s space exploration programs, including the new Space Launch System being developed by the National Aeronautics and Space Administration (NASA) to replace the retired Space Shuttle fleet (Figure 1).

The engines of these rockets rely on carefully prepared solid mixtures of chemicals combined in precisely measured amounts. Igniting the mixture initiates a vigorous chemical reaction that rapidly generates large amounts of gaseous products. These gases are ejected from the rocket engine through its nozzle, providing the thrust needed to propel heavy payloads into space. Both the nature of this chemical reaction and the relationships between the amounts of the substances being consumed and produced by the reaction are critically important considerations that determine the success of the technology.

This chapter will describe how to symbolize chemical reactions using chemical equations and how to determine the quantitative relations between the amounts of substances involved in chemical reactions—that is, the reaction stoichiometry .

• Chemistry. Provided by : OpenStax College. Located at : http://openstaxcollege.org . License : CC BY: Attribution . License Terms : Download for free at https://openstaxcollege.org/textbooks/chemistry/get

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Introduction to stoichiometry and moles

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• What is stoichiometry?
• Ratios in chemical reactions.
• Avogadro's number, moles and molar mass.
• Percentage composition by mass.
• Example: Find percentage composition and empirical formula.
• How many moles of H 2 _2 2 ​ O were produced if 2.5 moles of CO 2 _2 2 ​ were produced?
• What is the mass of 2.5 moles of CO 2 _2 2 ​ ?
• In a repeat experiment, 132 grams of CO 2 _2 2 ​ were produced. What was the mass of water also produced?
• How many moles of HCI are required to react with 4.75 moles of NaOH?
• What would be the mass of 4.5 moles of NaOH?
• In a repeat experiment, 54.75g HCI (dissolved in solution) reacted completely with some NaOH added. What was the mass of NaOH used in this experiment?
• How many moles of O 2 _2 2 ​ would react with 1 mole of C 2 _2 2 ​ H 6 _6 6 ​ ?
• If 15 moles of H 2 _2 2 ​ O were produced in this experiment, how many moles of C 2 _2 2 ​ H 6 _6 6 ​ were used?
• What is the mass of this amount of C 2 _2 2 ​ H 6 _6 6 ​ used?
• A total of 0.19 mol of reactants and products combined were involved in this reaction. What is the number of moles of H 2 _2 2 ​ O produced?
• Ca in CaCO 3
• H in C 6 H 6
• A compound has the following percentage composition by mass: C 52.2%; H 13.0%; O 34.8%. What is the empirical formula of this compound?

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Topic Notes

• The mole concept and its importance to the amount of chemical substance.
• To predict amounts of product made in a reaction with a given amount of reactant.
• To apply and convert moles to find mass of reactants and products in reactions.
• To calculate percentage composition by mass of atoms in a chemical substance.
• The stoichiometry of a reaction is the ratio of different amounts of each reactant that is needed to run a chemical reaction . As you should have seen previously, recall that:
• Matter is particulate in nature; we call these matter particles atoms .
• The 100 or so known unique atoms (the elements ) can combine in unique arrangements of fixed ratios to form new chemical substances . This is what a chemical reaction is, and these combined arrangements of atoms are called molecules. The ratios of the different atoms combining does not depend on how the substance is prepared. This principle is known as the law of definite proportions or Proust’s law.
• Reactions take place between fixed integer ratios of the reactants . For example, the reactants are two molecules of A and one atom of B which combine to make one molecule of product C. To make C, you need A and B in that ratio. This is like making a coffee: if the liquid in a coffee takes four parts hot water and one part milk, to make two servings you increase the amounts to make more but keep the ratio of them the same .
• Real atoms and molecules are far too small to count in an ordinary laboratory without special equipment.
• Different atoms and molecules have different masses . 50 grams of one substance will not contain the same number of molecules as 50 grams of another.
• Recall from Introduction to chemical equations that a chemical equation tells you the fixed ratio of reactants the reaction uses, and products that the reaction produces.
• In the example below, we are being told that to produce 1 molecule of C, the reaction needs 1 molecule of A and 2 molecules of B in that fixed ratio . Again, like coffee with one part milk and four parts hot water: if you want to make coffee for two, you must add twice as much milk and water in the same ratio. This is what the “stoichiometry of the reaction” is.
• As said above, atoms are so small they cannot be counted with regular laboratory equipment, so chemists use mass which is easily measurable to get the amounts they need. The mass of a substance is related to the number of moles of the substance.
• For example, carbon dioxide or CO 2 has a molecular mass of 44 grams per mole (g mol -1 ). That means that 1 mole (six hundred billion trillion molecules) of carbon dioxide has a mass of 44 grams. A sample of 22 grams of CO 2 would be 0.5 moles of CO 2 .
• The mole is important because we can now find out the correct amounts of substance needed in a reaction by using molar mass (from the periodic table) and mass which is very easy to measure.
• The idea of fixed ratios of amounts of substance applies to atoms within compounds too. Compounds are formed by fixed ratios of elemental atoms combining and the method of preparation does not affect this (Proust’s law), so a given compound will always have the same composition by mass of its elements .
• For example, no matter how you make CO 2 , its molar mass is 44 g mol -1 and O 2 provides 32 g mol -1 of this mass. This is 73% of the mass of CO 2 from oxygen; all CO 2 molecules will be 73% oxygen as a percentage composition by mass .
• WORKED EXAMPLE: Using percentage composition to find empirical formula.

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