Chapter 3 Section 4
Notes
Using Moles to Count Atoms
What is a mole?

The SI base unit that describes the
amount of a substance; a collection of a
very large number of particles.
What is a mole useful for?

Counting small particles
Avogadro’s Constant

Avogadro’s Constant: the number of
particles in 1 mol
6.022 x 1023 particles/ mol
 602,213,670,000,000,000,000,000 particles
 Equals

How does Avogadro’s constant relate to a
mole of something?
 It
is the number of particles in one mole of
anything.
Moles and Grams are related
Molar Mass: the mass in grams of 1 mol of
a substance
 How do you find molar mass?

 The
average atomic mass is equal to molar
mass.
 Simply look on the Periodic Table!
Practice

Determine the molar mass of the following
elements: (Round to the nearest hundredth)
 Manganese, Mn
 54.94 g/mol
 Cadmium, Cd
 112.41 g/mol
 Arsenic, As
 74.92 g/mol
 Strontium, Sr
 87.62 g/mol
More Practice

Determine the mass, in grams of each of
the following:
 0.48
0.48 mol x
mol of platinum
195.08 g
1 mol
= 94 g
 2.50
mol of sulfur
2.50 mol x
32.07 g
1 mol
=
80.2 g
Even More Practice

Determine how many moles are present in
each of the following:
 620
620 g x
g of mercury
1 mol
= 3.09 mol
200.59 g
 11
g of silicon
11 g x
1 mol
28.09 g
= 0.39 mol
Compounds also have molar mass
To find the molar mass of a compound,
add up the molar masses of all the atoms
in a molecule of the compound.
 Example: H2O

 Molar
Mass of Hydrogen: 1.01 x 2 = 2.02 g/mol
 Molar Mass of Oxygen: 16 g/mol

Total Mass of H2O: 2.02 g + 16 g = 18.02 g/mol