JOURNAL #67
What
is a chemical formula?
Provide an example of a
chemical formula.
TODAY WE WILL LEARN HOW TO
USE CHEMICAL FORMULAS
MOLAR MASS REVIEW:

Give the molar mass of the following elements:
Na
2. C
3. O
4. Xe
1.
CAN YOU GUESS THE
COMPOUND?
1.
2.
H2O
NaCl
MOLAR MASS OF A
FORMULA MASSES
Previously, we saw that hydrogen atoms have an
average atomic mass of 1.00794 amu and oxygen has
an average atomic mass of 15.9994 amu.
 Like individual atoms, molecules or ions have
characteristic average masses
 Example: H2O is composed of 2 hydrogens and 1
oxygen. The average atomic mass can be calculated:

2 H atoms x 1.01 amu = 2.02 amu
H atom
1 O atom x 16.00 amu= 16.00 amu
O atom
average atomic mass of H20 = 18.02 amu
FORMULA MASS
 The
mass of a water molecule can be
referred to as a molecular mass.
 The mass of one NaCl formula unit, is not
a molecular mass because NaCl is an ionic
compound.
 The mass of any unit represented by a
chemical formula, where the unit is a
molecule, a formula unit, or an ion is
known as the formula mass.
FIND THE FORMULA MASS OF THE FOLLOWING:
1.
2.
3.
4.
5.
KClO3
H2SO4
Ca(NO3)2
PO43MgCl2
MOLAR MASS
 Molar
mass of a substance is qual to the
mass in grams of one mole (or 6.022 x 10
^23 particles)
 Example: molar mass of Ca is 40.08g/mol
because calcium atoms has a mass of
40.08g
 The molar mass of a compound is
calculated by summing the masses of the
elements present in a mole of the
molecules or formula units that make up
the compound.
MOLAR MASS
A
compounds molar mass is numerically
equal to its formula mass.
Example:
2 H atoms x 1.01 g H
1 mol H
1 O atom x 16.00 g O
1 mol O
molar mass of H20
= 2.02 g H
= 16.00 g O
= 18.02 g/mol
WHAT IS THE MOLAR MASS OF THE FOLLOWING:
1.
2.
3.
4.
Ba(NO3)2
Al2S3
NaNO3
Ba(OH)2
CONVERSION FACTOR
Molar mass of a compound can be used as a
conversion factor to relate the amount in moles to
a mass in grams for a given substance.
 To convert a known amount of a compound in
moles to a mass in grams, multiply the amount in
moles by the molar mass.
 Example: what is the mass in grams of 2.50 mol
of oxygen gas?

EXAMPLE:
Ibuprofen, C13H18O2 is the active ingredient in
many nonprescription pain relievers. Its molar
mass is 206.31g/mol.
 If the tablets in a bottle contain a total of 33g of
ibuprofen, how many moles of ibuprofen are in
the bottle?
 How many molecules of ibuprofen are in the
bottle?
 What is the total mass in grams of carbon in 33g
of ibuprofen?