Unit 9: Stoichiometry

Were you surprised when you see the purple color of potassium permanganate disappear as you added sodium hydrogen sulfite? If you concluded that the potassium permanganate has been used up and the reaction stopped, you are right. What would happen if a bell jar was lowered over a burning candle blocking off the supply of oxygen? You know that oxygen is needed for the combustion of candle wax, so when the oxygen inside the bell jar is used up, the candle will go out.

Chemical reactions, such as the reactions listed above, stop when one of the reactants is used up. Thus, in planning the reactions, a chemist needs to know how many grams of each reactant are needed to make the reaction go to completion. For the reactions above, you might ask, “How much oxygen is required to completely burn a candle of known mass, or how much product will be produced if a given amount of a reactant is used?” Stoichiometry is the tool for answering these questions.

Why is this important to us? The cost of the things you buy is lower because chemists use stoichiometric calculations to increase efficiency in laboratories, decrease waste in manufacturing, and produce products more quickly.

In this unit, you will:

1. Write mole ratios from balanced chemical reactions.

2. Calculate the number of moles and the mass of a reactant or product when given the number of moles or the mass of another reactant or product.

3. Identify the limiting reactant in a chemical reaction.

4. Determine the percent yield of a chemical reaction.

ª Notes

o Power Point

o Stoichiometric Calculation Formulas

o Limiting Reactants

ª Homework

o Mole Ratios and Moles-Moles

o Mass-Moles and Moles-Mass