Module 6 Intro

Module 6—Stoichiometry

Lesson Summary

 

In this lesson you investigated the following questions:

• How are predictions made about the masses of reactants and/or products involved in chemical reactions?
  
  

• How can you test the predictions made using the stoichiometric method?
  
  

• What is percent yield and how can it be determined?

The procedure for calculating the masses of reactants or products in a chemical reaction is called gravimetric stoichiometry. There are four steps in solving any gravimetric stoichiometry problem:

 

Step 1: Write a balanced chemical equation, and list the given information—the masses and molar masses of the known and desired substances.

 

Step 2: Convert the mass of the known substance into number of moles.

 

Step 3: Use the mole ratio to convert the number of moles calculated in Step 2 into the number of moles for the desired substance.

 

Step 4: Calculate the mass of the desired substance using the number of moles calculated in Step 3.

 

You discovered that the stoichiometric method can be tested by comparing predicted values with data collected through experimentation. You also calculated the percent difference and found that percent difference is a useful way to determine the validity of predictions made using the stoichiometric method.

 

You also calculated percent yield. Percent yield is the ratio of the difference between the actual experimental quantity of product obtained and the maximum possible theoretical quantity of product (as determined by the stoichiometry method). In Lesson 3 you will use percent yield to assess the results of an experiment.

 

Lesson Glossary

 

gravimetric analysis: the determination of masses of substances

 

yield of a reaction: a measured quantity of product obtained by a chemical reaction, often expressed as a percentage of maximum yield

 

Chemistry 20 © 2008 Alberta Education