THE HEART OF
STOICHIOMETRY
A
BALANCED
EQUATION
1
Proportional Relationships

Stoichiometry
 mass relationships between substances
in a chemical reaction
 based on the mole ratio

Mole Ratio
 indicated by coefficients in a balanced
equation
2 Mg + O2  2 MgO
2
Proportional Relationships
2 1/4 c. flour
1 tsp. baking soda
1 tsp. salt
1 c. butter
3/4 c. sugar

3/4 c. brown sugar
1 tsp vanilla extract
2 eggs
2 c. chocolate chips
Makes 3 dozen cookies.
I have 5 eggs. How many cookies can I
make?
5 eggs
3 doz.
2 eggs
Ratio of eggs to cookies
= 7.5 dozen cookies
3
HOW TO SOLVE PROBLEMS

There are four basic types of
problems:




Mole to mole
Mole to gram
Gram to mole
Gram to gram
4
MOLE TO MOLE PROBLEMS
X Moles A is the amount given in the
problem
 Moles A to Moles B is the mole ratio
from your equation.
 The coefficients are the mole ratio!

X mol A
mol B
mol A
= mol B
5
2H2 + O2  2H2O
 If
you have 12 moles of oxygen,
how many moles of water will you
make?
12 mol O2 2 mol H2O
1 mol O2
(from problem)
= 24 mol H2O
(from equation)
6
You try one
Write and balance:
sodium + fluorine sodium fluoride
If you have 5.50 moles of sodium,
how many moles of fluorine do you
need?
7
2Na + F2  2NaF

If you have 5.50 moles of sodium,
how many moles of fluorine do you
need?
5.50 mol Na
1 mol F2
2 mol Na
(from problem)
= 2.75 mol F2
(from equation)
8
MOLE TO GRAM
PROBLEMS

You have to find the molar mass of
compounds to solve these problems.
X mol A
mol B
grams B
mol A 1 mol B
(from problem) (from equation)
= grams B
(from periodic table)
9
2Na + F2  2NaF
If you have 18 moles of fluorine,
how many grams of NaF will you
make?
 First, find the g/mol of your
compound
 Then, set up your problem.
 You must use labels in the problem!!
 Check your sig figs!

10
Find the mass of NaF, then
set up the problem
23g Na + 19g F = 42g/mol NaF
18 mol F2 2 mol NaF 42 g NaF
1 mol F2
(from problem) (from equation)
1 mol NaF
= 1500 g NaF
(from periodic table)
11
2Na + F2  2NaF

If you have 25.0 moles of Na, how many
grams of fluorine will you need?
25.0 mol Na 1 mol F2
2 mol Na
(from problem)
(from equation)
38g F2 = 475 g F
2
1 mol F2
(from periodic table)
12
GRAM TO MOLE
PROBLEMS

You have to find molar mass of
compounds to solve these problems, too.
gram A
1 mol A
gram A
mol B
mol A
= mol B
(from problem) (from periodic table) (from equation)
13
4K + O2  2K2O

If you have 245g K, how many moles
of K2O will you produce?
245g K
1 mol K
2 mol K2O
39 g K
4 mol K
= 3.14
mol K2O
14
GRAM TO GRAM
PROBLEMS
These are the longest problems of
all.
 You have to find the molar mass of
several compounds to solve the
problems.
 You must have labels in every part
of your equation!

15
GRAM TO GRAM
PROBLEMS
Now is not the time to take
shortcuts! I will mark them wrong!
 Do not combine any equalities or skip
any equalities.
 My way is the only way!

16
GRAM TO GRAM
PROBLEMS
X grams A 1 mol A
mol B
grams B
grams A
mol A
1 mol B
(from P.T.)
(from equation)
(from P.T.)
(from problem)
=gB
17
2NaOH + H2SO4  Na2SO4 + 2H2O
If you have 95 grams of sodium
hydroxide, how many grams of
sulfuric acid will you need?
 First, find g/mol of both sodium
hydroxide and sulfuric acid.

Na = 23
2H =
1 O = 16
1 S = 32
1H= 1
4 O = 64
40g/mol
2
98g/mol
18
The set-up
95 g NaOH 1 mol NaOH
1 mol H2SO4 98 g H2SO4
40 g NaOH
2 mol NaOH 1 mol H2SO4
= 116 g H2SO4
19
Use the same information and
equation to solve the following:
How many grams of each product will be produced?
 First, find the molar mass of each product.
Na = 2(23) = 46
H = 2 (1) = 2
S = 1(32) = 32
O = 4(16) = 64
O = 1(16) = 16
18g/mol
142 g/mol
20
2NaOH + H2SO4  Na2SO4 + 2H2O
95g NaOH 1 mol NaOH
40g NaOH
95g NaOH 1 mol NaOH
40g NaOH
1 mol Na2SO4 142 g Na2SO4 =
2 mol NaOH 1 mol Na2SO4
2 mol H2O
2 mol NaOH
18 g H2O
1 mol H2O
=
g Na2SO4
g H2O
21
Solution

168.63 g Na2SO4

42.75 g H2O
22