Stoichiometry
The Mole

A counting unit

Similar to a dozen, except instead
of 12, it’s
602,000,000,000,000,000,000,000

6.02 X 1023 (in scientific notation)

This number is named in honor of
Amedeo Avogadro (1776 – 1856)
Molar Mass

The mass of 1 mole (in grams)

Equal to the numerical value from periodic
table, or add the mass of the atoms together
for a molecule
1 mole of C atoms
=
12.0 g
1 mole of Mg atoms
=
24.3 g
1 mole of O2 molecules
=
32.0 g
Molar Mass of Compounds

The molar mass (MM) of a compound is
determined the same way, except you add up
all the atomic masses for the molecule
Ex. Molar mass of CaCl2
 Avg. Atomic mass of Calcium = 40.08g
 Avg. Atomic mass of Chlorine = 35.45g
 Molar Mass of calcium chloride =
40.08 g/mol Ca + (2 X 35.45) g/mol Cl
 110.98 g/mol CaCl2

20
Ca
40.08
17
Cl
35.45

Formula Units

A term to describe an ionic or covalent
compound.
Atoms
Multiply by
number of
atoms in
formula
Flowchart
Divide by
number of
atoms in
formula
Formula Units
Divide by 6.02 X 1023
Multiply by 6.02 X 1023
Moles
Divide by
atomic/molar mass
from periodic table
Multiply by
atomic/molar mass
from periodic table
Mass
(grams)
Practice

Calculate the Molar Mass of
calcium phosphate
 Formula =
Ca3(PO4)2

Masses elements:




Ca: 3 Ca’s X 40.1 =
P: 2 P’s X 31.0 =
O: 8 O’s X 16.0 =
Molar Mass =
120.3 g
62.0 g
128.0 g
120.3g
310.3
+ 62.0g
g/mol
+128.0g
Calculations
molar mass
Grams
Avogadro’s number
Moles
particles
Everything must go through
Moles!!!
Atoms/Molecules and Grams
How many moles of Cu are
present in 35.4 g of Cu?
How many atoms would that be?
Learning Check!
What is the mass (in grams) of
1.20 X 1024 molecules of
glucose (C6H12O6)?
Hint: convert to moles first,
then to grams.
Practice
1. How many atoms in total are indicated in
(a) NH4NO3
(b) Mg3(PO4)2
2. How many formula units (molecules) are in
3 moles of NH4NO3? How many atoms is that?
3. How many moles are in 5.64 x 1021 molecules
of Mg3(PO4)2?
4.How many moles are in 9.52 x 1031 atoms of
Mg3(PO4)2?
Mass to atoms (and back)
5. How many H atoms are in 2.3g of water?
6. Determine the mass of 6.7 x 1012
molecules of water.
7. Determine the number of atoms contained
in 1.2 g of NaCl
Complete Mole Calculations Worksheet
 Read pg 47-50
Complete #5-11, pg 52

Stoichiometry
Chocolate Chip Cookies!!
1 cup butter
1/2 cup white sugar
1 cup packed brown sugar
1 teaspoon vanilla extract
2 eggs
2 1/2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon salt
2 cups semisweet chocolate chips
Makes 3 dozen
How many eggs are needed to make 3 dozen cookies?
How much butter is needed for the amount of chocolate chips used?
How many eggs would we need to make 9 dozen cookies?
How much brown sugar would I need if I had 1 ½ cups white sugar?
Cookies and Chemistry…Huh!?!?




Just like chocolate chip
cookies have recipes,
chemists have recipes as well
Instead of calling them
recipes, we call them reaction
equations
Furthermore, instead of using
cups and teaspoons, we use
moles
Lastly, instead of eggs, butter,
sugar, etc. we use chemical
compounds as ingredients
Chemistry Recipes

You need a balanced reaction before you
start!
2 Na + Cl2  2 NaCl
 This reaction tells us that by mixing 2 moles of Na
with 1 mole of Cl2we will get 2 moles of NaCl
 Ex:
 What
if we wanted 4 moles of NaCl? 10 moles?
50 moles?
Practice

Write the balanced rxn for hydrogen gas reacting
with oxygen gas to produce water



2 H2 + O2  2 H2O
2 mol H2
1 mol O2
Moles of reactants are needed?
4 mol H
What if we wanted 4 moles of water? 2 mol O2
2
If we had 3 moles of O2, how much H2 would we need?
How much water would we get?
6 mol H2, 6 mol H2O

If we had 50 moles of hydrogen, how much oxygen
would we need? How much water produced?
25 mol O2, 50 mol H2O
Mole Ratios


Mole ratios can be used to calculate the moles
of one chemical from the given amount of a
different chemical
Ex: How many moles of Cl2 are needed to react
with 5 moles of Na (using all the Na)?
2 Na + Cl2  2 NaCl
5 moles Na 1 mol Cl2
2 mol Na
= 2.5 moles Cl2
Mole-Mole Conversions

How many moles of NaCl will be produced
if you react 2.6 moles of Cl2 with an
excess of Na?
2 Na + Cl2  2 NaCl
2.6 moles Cl2 2 mol NaCl
1 mol Cl2
= 5.2 moles NaCl
Mole-Mass Conversions


Amounts of a chemical are often given in grams
instead of moles
We still go through moles and use the mole ratio,
but now we also use molar mass to get to grams
 Ex:
How many grams of Cl2 are required to react
completely with 5.00 moles of Na to produce NaCl?
2 Na + Cl2  2 NaCl
5.00 moles Na 1 mol Cl2
2 mol Na
70.90g Cl2
1 mol Cl2
= 177g Cl2
You Practice

Calculate the mass in grams of iodine
required to react completely with 0.50
moles of Al.
2 Al + 3 I2  2 AlI3
Mass-Mole
We can also start with mass and convert to
moles of product or another reactant
 We use molar mass and the mole ratio to get
to moles of the compound of interest

Calculate the number of moles of ethane (C2H6)
needed to produce 10.0 g of water
 2 C2H6 + 7 O2  4 CO2 + 6 H20

10.0 g H2O 1 mol H2O
2 mol C2H6 = 0.185
18.0 g H2O 6 mol H20
mol C2H6
Mass-Mass Conversions

Most often we are given a starting mass
and want to find out the mass of a product
(called theoretical yield) or how much of
another reactant we need to completely
react with it (no leftovers!)
Steps for Mass to Mass
1.
2.
3.
Grams to moles of given substance
Mole ratio
Moles to grams of compound
Mass-Mass Conversion
Ex. Calculate how many grams of
ammonia are produced when you react
2.00g of nitrogen with excess hydrogen.
 N2 + 3 H2  2 NH3

2.00g N2
1 mol N2
2 mol NH3
28.02g N2 1 mol N2
= 2.4 g NH3
17.06g NH3
1 mol NH3
Read pg 110-114
Do: #4-7 pg 115
#9 & 10 pg 117
19 & 20 pg 125

#Check your answers on pg 151
Practice

How many grams of calcium nitride are
produced when 2.00 g of calcium reacts
with an excess of nitrogen?
Practice

(a)
(b)
(c)
Given the equation C + O2  CO
Balance the equation
How many moles of O2 are required to
react with 2.36 moles of C?
How many moles of CO will be formed
from 5.9 moles of C reacting?