Solving Stoichiometry Problems
Objectives:
1. Name four major categories of
stoichiometry problems.
2. Explain how to solve each type of
stoichiometry problems.
Notes:
It is important to remember that solving
stoichiometry problems is very similar to following a recipe. Once you
know the recipe you can modify it using the same ratios to make the product for
more or less people.
There are 4 major categories of stiochiometry
problems. It is important to remember, though, that in every situation you
need to start out with a balanced equation.
1. Mole-Mole Problems
Problem: How many moles of HCl are needed
to react with 0.87 moles of Al?
Step 1:
Balance The Equation & Calculate the Ratios


2Al:6HCl
(1:3) 2Al:2AlCl3
(1:1) 2Al:3H2 (1:1.5)
Step 2:
Find the Moles of the Given
0.87 moles
of aluminum are reacted with hydrochloric acid
Step
3: Calculate the moles using the ratios
moles HCl = 0.87molAl x 3molHCl/1molAl = 2.6 mol HCl

2. Mass-Mass Problems
(Strategy: Mass g
Mole g
Mole g
Mass)
Problem: How many grams of Al can be
created decomposing 9.8g of Al2O3?
Step 1: Balance
The Equation & Calculate the Ratios


2Al2O3:4Al
(1:2) 2Al2O3:3O2
(1:1.5)
Step 2: Find the Mass of the Given
9.8g Al2O3
are decomposed
Step 3: Calculate the moles of the given (mol/g)
9.8g Al2O3
x (1mol Al2O3/102g Al2O3) = 0.096
mol Al2O3

Step 4: Calculate the moles using the ratios
0.096 mol Al2O3
x (2 mol Al/1 mol Al2O3) = 0.19 mol Al

Step 5: Calculate the
mass using the new moles
0.19
mol Al x (27g Al/1 mol Al) = 5.1g Al

3. Mass-Volume Problems
(Strategy: Mass g
Mole g
Mole g
Volume)
Problem:
How many liters of H2 are created from the reaction of 20.0g K?
Step 1:
Balance The Equation & Calculate the Ratios


2K:2H2O
(1:1) 2K:2KOH (1:1) 2K:1H2 (2:1)
Step 2: Find the Mass of the Given
20.0g K
are used in the reaction
Step 3: Calculate the moles of the given (mol/g)
20.0g K x
(1 mol K / 39g K) = 0.513 mol K

Step 4: Calculate the moles using the ratios
0.51 mol K
x (1mol H2 /2mol K) = 0.266mol H2

Step 5: Calculate the
volume using the new moles
0.266 mol H2
x (22.4L H2 /1mol H2) = 5.75L H2

4. Volume-Volume Problems
Problem: How many liters of SO2
will be produced from 26.9L O2?
Step 1:
Balance The Equation & Calculate the Ratios


2O2:1S2
(2:1) 2O2:2SO2 (1:1)
Step 2: Find the volume of the given
26.9L O2
Step 3: Calculate the moles of the given
26.9L O2
x
(1 mol O2 / 22.4L) = 1.20 mol O2

Step 4: Calculate the moles using the ratios
1.20 mol O2
x (1mol SO2 /1mol O2) = 1.20 mol SO2
Step 5: Calculate the
volume using the new moles
1.20 mol O2
x (1mol SO2 /1mol O2) x (22.4L /1mol) = 26.9L SO2
