It’s time to learn about . . .
Stoichiometry: Conversions
At the conclusion of our time together,
you should be able to:
1. Convert a mole of a chemical to particles or
grams of that chemical
2. Convert grams of a chemical to moles or
particles
3. Convert particles of a chemical to moles or
grams
Molar Mass of Molecules and
Compounds
Mass in grams of 1 mole is equal
numerically to the sum of the atomic masses
1 mole of CaCl2
=
1 mole Ca x
40.08 g/mol
+ 2 moles Cl x
35.45 g/mol
=
110.98 g/mol CaCl2
1 mole of N2O4
=
92.02 g/mol N2O4
Other Names Related to Molar Mass

Molecular Mass: If you have a single molecule, mass is
measured in amu’s instead of grams. The molecular mass
is the same numerical value as 1 mole of molecules, only
the units are different - grams and not amu’s.

(This is the beauty of Avogadro’s Number!)

Formula Mass: Same goes for ionic compounds. But
again, the numerical value is the same, only the units are
different.
Calculations with Molar Mass
molar mass
Grams
Moles
Molar Mass as a Conversion Factor
Molar Mass of the Compound
1 mole
or
1 mole
Molar Mass of the Compound
Note that the molar mass could be that of an atom
OR a molecule!
Example of Converting Moles to
Grams
Aluminum is often used for the
structure of light-weight bicycle
frames. How many grams of Al are in
3.00 moles of Al?
3.00 moles Al
? g Al
1. Molar mass of Al 1 mole Al = 26.98 g Al
2. Conversion factors for Al
26.98 g Al
or
1 mol Al
1 mol Al
26.98 g Al
3. Setup
3.00 moles Al
Answer
x
26.98 g Al
1 mole Al
= 80.94 g Al
Learning Check!
The artificial sweetener aspartame
(Nutra-Sweet) formula C14H18N2O5 is
used to sweeten diet foods, coffee and
soft drinks. How many moles of
aspartame are present in 225 g of
aspartame?
= 0.764 mol
Avogadro’s Number as a
Conversion Factor
6.02 x 1023 particles
1 mole
or
1 mole
6.02 x 1023 particles
Note that a particle could be an atom OR a
molecule!
Example of Avogadro’s Number as a
Conversion Factor
1. Number of molecules in 4.50 mole of NaCl
2.Number of moles of H2O in 6.62 x 1024
molecules
Atoms/Molecules to Grams

Since 6.02 X 1023 particles = 1 mole
and
1 mole = molar mass (grams)

You can convert atoms/molecules to
moles and then moles to grams!
(Two step process)

You can’t go directly from atoms to
grams!!!! You MUST go thru MOLES.
Calculations
molar mass
Grams
Avogadro’s number
Moles
particles
Everything must go through Moles!!!
Atoms/Molecules to Grams
How many atoms of Cu are present
in 35.4 g of Cu?
35.4 g Cu
x 1 mol Cu
63.55 g Cu
x 6.02x1023 atoms Cu
1 mol Cu
= 3.35 X 1023 atoms Cu
Grams to Atoms/Molecules
How many grams of Cu are present in
5.4 x 1023 atoms of Cu?
5.4 x 1023 atoms Cu
x 1 mol Cu
6.02 x 1023 atoms Cu
x 63.55 g Cu
1 mol Cu
= 57 g Cu
Stoichiometry: Conversions
Let’s see if you can:
1. Convert a mole of a chemical to particles or
grams of that chemical
2. Convert grams of a chemical to moles or
particles
3. Convert particles of a chemical to moles or
grams
Learning Check!
How many atoms of O are present in 78.1 g
of oxygen?
78.1 g O2 1 mol O2 6.02 X 1023 molecules O2 2 atoms O
32.0 g O2 1 mol O2
1 molecule O2
2.94 x 1024 atoms of O
Learning Check
Prozac, C17H18F3NO, is a widely used
antidepressant that inhibits the uptake of
serotonin by the brain. Find its molar
mass.
309.36 g/mol
Learning Check!
How many atoms of K are present in 78.4 g
of K?
= 1.21 x 1024 atoms of K
Learning Check!
What is the mass (in grams) of 1.20 X 1024
molecules of glucose (C6H12O6)?
= 327 g of glucose