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 ! ! !
Example 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?

Example 2: 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?
Example 3:

Liquid bromine is reacted with aluminum to produce aluminum
bromide.


2Al(s) + 3Br2 (l)
2AlBr3 (s)
If 450 ml of bromine reacts with excess aluminum, how much
aluminum bromide will be made? The density of bromine is 3.1 g/ml
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.
Example 4:
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?
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.)
Example 5:
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?
Solution Stoichiometry
Solutions

Uniform mixtures, composition is the same throughout

Solvent—substance doing the dissolving, present in a larger amount.

Solute—dissolved substance, present in a smaller amount

Examples: sugar in tea, salt water
Concentration

Amount of solute
amount of solvent or solution

How much “stuff” is in a solution

Solute quantity in a certain amount of solvent/solution

Usually seen as mass percent value
Ex. Orange juice, sweet tea
Molarity (M)

Main unit of concentration in chemistry

Moles solute
L solution

Many solutions provide only the % solute by mass

need to know density to get molarity
Example 6:
What is the concentration/molarity of a 50.0 ml solution with 1.25g of
CuSO4 in water?
Example 7:
Luke Skywalker has a stock solution of aqueous formic acid that is 90%
HCOOH by mass. The density of this solution is 1.20 g/ml. Skywalker
wants to know the molarity of this solution to determine if it can be
used in the construction of his latest project: starship destroyer X.
More Molarity Practice
1)
A 500 ml solution of NaOH has a molarity of 0.50M. How many
moles of NaOH are in the solution?
2) You have two solutions. One solution has 500 ml of 0.20 M NaCl and
the other solution has 250 ml of 0.25 M NaCl.Which solution is more
concentrated?
3) 2.75g of AgNO3 dissolved in 0.250 L of solution. Find the molarity.
4) How many grams of H2SO4 are needed to make a 5M
concentration solution with 250 ml?
Dilutions
Often want to prepare solutions of LESS concentration than stock
solution
 Technique of preparing a less concentrated solution by adding more
solvent to decrease the solution’s concentration
 Solute amount remains the same SOOO

M1V1
 M1/V1
= M2V2
values indicate initial “concentrated”
solution
 M2/V2 values indicate final “dilute” solution
Example 8:
Baking soda (NaHCO3) neutralizes HCl in the following reaction when
175 ml of 1.55 M NaHCO3 is added to 235 ml of 1.22 M HCl.
NaHCO3 (aq) + HCl (aq)
NaCl (aq) + H2O (l) + CO2 (g)
a)
How many grams of CO2 are given off?
b)
What is the molarity of the aqueous NaCl solution?
Example 9:

Household bleach can be produced based on the chemical
reaction below.

2NaOH(aq) + Cl2 (g)
NaOCl (aq) +
NaCl (aq) +
H2O (l)

a) What volume of 0.25M NaOH is required to produce 18g of NaOCl?

b) what volume of 0.25M NaOH is required to react with 0.32 moles of
chlorine?

c) If 4.00L of 0.25M NaOH are used with excess chlorine gas, how much
NaOCl is produced?
Homework:

Finish Stoichiometry Sheet

Percent Water Lab Report