Stoichiometry
The Basics
 What is stoichiometry?
 A method of determining the quantities of products produced
in a chemical reaction or what amount of a reactant needed
to carry out a chemical reaction.
 What do the stoichiometric coefficients tell us about the
chemical reaction and the ratio between the chemical
compounds involved?
MOLE RATIO ! ! !
Ex. 1
Milk of magnesia, Mg(OH)2, reacts with stomach acid in a
neutralization reaction. What is the mass (in grams) of
magnesium chloride produced when 3.00g of milk of
magnesia is taken?
More Practice with the Basics
1) _____N2H4 + ____O2
fuel)
 ____N2 + _____H2O (N2H4 is rocket
We have 5.20 mol of N2H4. How many moles of O2 do we use up in
the reaction?
2) ____C6H12O6
+ ____O2  ____CO2 + _____H2O
If you eat 10.0 grams of sugar, how many grams of oxygen do you
need to breathe to carry out this reaction and get energy?

True Test of Stoichiometry
Skills
Gaseous ammonia is placed into an aqueous solution that
is 65% H2SO4 by mass with a density of 1.55 g/mol.
Ammonium sulfate is produced from this reaction and
used as fertilizer. How many milliliters of sulfuric acid are
needed along with 1.00 kg NH3 to produce ammonium
phosphate?
Limiting Reactant
 Chemical compound that “limits” or determines how
much product can be produced
 All of the compound is consumed in the reaction
 Excess reactant—chemical compound not consumed
in the reaction, plenty of the compound is available for
the chemical reaction
Steps to find the limiting
reactant
 Two stoichiometry problems in ONE ! 
1) Write a balanced equation
2) Find the amount of product (in grams) produced from
each reactant amount.
3) The reactant producing the SMALLEST product is the
limiting reactant.
Ex. 2
Aspirin synthesis:
2C7H6O3 + C4H6O3
2C9H8O4 + H2O
When 20.0g of C7H6O3 and 20.0g of C4H6O3 react, which
is the limiting reactant? What is the mass (in grams) of
aspirin produced?
Limiting Reactant—More
Practice
1) For the thermite reaction between chromium(III) oxide
and aluminum metal, producing chromium metal and
aluminum oxide, what is the maximum weight of metallic
chromium that can be produced by reacting 38.0 grams of
Cr2O3 with 9.00 grams of metallic aluminum?
2) What mass of of magnesium oxide is formed when
10.0g of magnesium metal reacts with 10.0g of oxygen?
Percent Yield
 “yield—” the amount of product actually made through a
chemical reaction. Why is this value important?
 Theoretical yield— calculated amount of product
 Actual/Experimental yield– the “true/actual” amount of
product made in the chemical reaction, usually less than
theoretical
 How is this value different than percent error?
Percent Yield
 = Actual yield
x 100%
Theoretical yield
Ex. 98.80% of Mg3N2 was produced in a chemical
reaction. What happened to the rest? (purity, other
reactions, remaining product, etc.)
Consider the reaction between solutions of barium
hydroxide and phosphoric acid, which forms water and
quantitatively precipitates barium phosphate. A student
mixes 500.0 mL of 0.0400 M H3PO4 with 240.0 mL of
0.100 M Ba(OH)2 and collects 4.66 grams of a white
precipitate.
1) Which reactant was the limiting reagent?
2) What was the theoretical amount of precipitate that
should have been formed?
3) What is the percent yield for this experiment?
Homework
 Read over lab procedure
 Read pp. 97-106
 Stoichiometry Worksheet