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Mole (mol): The SI base unit that measures an
amount of a substance; 1 mole of molecules has a
mass equal to the molecular weight in grams.
1 mole = 6.02x1023 atoms (molecules)
When looking at a chemical reaction, the number of
moles are indicated by the coefficients in front of the
formula’s.
Avogadro’s Number: The number of molecules in
one mole for any substance;
1mole of particles = 6.02 x 1023
2 moles of particles = 12.04 x 1023
3 moles of particles = 18.06 x 1023 etc . . .
Calculating Molecular Formula
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When supplied with the Empirical Formula, and the
Molecular Mass, we are capable of calculating the
Molecular Formula with the following equation:
Mass MF
Mass EF
Example: The empirical formula is CH and the
molecular mass is 26, what is the molecular
formula?
Gram Formula Mass (GFM)
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The GFM is the total mass of any substance
(element or compound)
Example: K2CO3 (2 K atoms, 1 C atom, and
3 O atoms)
Mass K = 39g
Mass C = 12g
Mass O = 16g
(39x2) + (12x1) + (16x3) = 138 grams
The gram formula mass of K2CO3 = 138g
WHAT YOU KNOW!!!!
GFM = 1 mole = 6.02 x 1023 molecules = 22.4 L
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This is the most important information for you to
memorize in order to master this unit.
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The above means that the GFM of any substance
(element or compound) is the same thing as saying 1
mole of that substance, which is the same as saying
there are 6.02 x 1023 molecules of that substance,
which is the same as saying there is 22.4 L of that same
substance!!
MoleMass / MassMole
Converstions
Table T: mole = given mass
GFM
Example: If you have 54 grams of LiF, how
many moles do you have?
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Example: If you have 2.3 moles of CuCl2,
how many grams do you have?
Stoichiometry
Mole-Mole Problems:
 Answers how many moles of one element or compounds react
with a given number of moles of another element or
compound.
Example: How many moles of Ca are needed to react completely
with 6 moles of H2O in the following reaction:
Ca + 2H2O  Ca(OH)2 + H2
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2.
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4.
Cross out anything in the equation that the problem is not
considering.
Write the coefficient of each substance remaining under the
element or compound.
On top of the element or compound write the number of
moles given in the problem.
Set up a proportion:
Percent Composition
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The percentage by mass of each of the
elements in compound
Table T:
% composition = mass part x 100
mass whole
Example: What is the percent by mass of
magnesium in magnesium oxide (MgO)?
Percent Composition
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Hydrate: a compound that incorporates
water molecules into its fundamental solid
structure. The compound has a dot after it
followed by the number of water molecules
attached.
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Ex: CaSO4•2H2O (SOLVE THE GFM)
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The dot in the hydrate equates to an
addition sign when calculating the GFM of a
hydrate.