SCH3U
THE MOLE AND MOLAR MASS
Making Omelettes
-in cooking a convenient amount is a dozen or 12
# of omelettes
1
a dozen
2 dozen
recipe
2 eggs + 3 mushrooms + 1 pepper --> 1 omelette
The Mole: A Chemists' Dozen
 The mole is defined as the number or entities (atoms) in exactly 12.000 g of
Carbon-12
 A Mole, (mol) is the amount of substance containing 6.022 X 1023 of
anything, just as a dozen is the amount of substance containing 12 of
anything.
o 1 mole of sodium (Na) atoms is 6.022 x 1023 sodium atoms
o 1 mole of sodium chloride (NaCl) formula units contains 6.022 X
1023 formula units of NaCl
o 1 mole of monkeys are 6.022 x 1023 monkeys!
o
The word mole was introduced in about 1896 by Wilhelm Ostwald. It is derived
from a Latin term meaning a “heap” or “pile”
Avogadro's constant (NA) = 6.02 x 1023 of something
ex. 2 moles of eggs
3 moles of feathers
a mole of H atoms
ex.
H2O  2H + O
2 molecules of H2O  2 atoms of H + 1 atom of O
1 dozen molecules of H20  2 dozen atoms of H + 1 dozen atoms of O
1 mol H2O  2 mol of H + 1 mol of O
SCH3U
6.02 x 1023 molecules of H2O  12.04 x 1023 atoms of H + 6.02 x1023
atoms of O
18.02 g H2O  2.02 g H atoms + 16.00 g of O atoms
 Scientists have determined experimentally that there are 6.022 X 1023
carbon atoms in 12g of C-12.
 In other words, each atom of C-12 has a mass of 12 amu, and each mole of C12 atoms (6.022 x 1023 atoms) has a mass of 12 grams.
 Thus the mole allows us to easily convert atomic mass into mass in grams.
Mass of 1 atom (amu)
Mass of 6.022 x 1023 atoms (grams)
-Mass of one Al-27 atom is exactly 27 amu; mass of one mole of Al-27 atoms is
exactly 27 g
-Mass of one N-14 atom is exactly 14 amu; mass of one mole of N-14 atoms is
exactly 14 g
-Mass of one Cl- ion is exactly 35.45 amu; mass of one mole of Cl- ions is exactly
35.34 g
MOLAR MASS
- is the mass of one mole of a substance, SI unit = g/mol, SI symbol = M
- given on the periodic table
ex. the molar mass of oxygen is 16.00 g/mol
mass of one mole of He
molar mass of Na
molar mass of K
Molar Mass of Compounds
- the sum of the molar masses of its components
ex. mass of 1 mole of water
MH2O = MH x 2 + MO
= 1.01 g/mol x 2 + 16.00 g/mol
SCH3U
= 18.02 g/mol
-so 1 mole of water (or 6.02 x 1023 molecules of water) weighs 18.02 g
ex. molar mass of methane
MCH4
ex. calculate the molar mass of magnesium if 0.330 mol has a mass of 8.02 g
M mg = g/ mol
M mg = 8.02 g/0.330 mol
= 24.3 g/mol
ex. calculate the molar mass of an element if 2.220 mol has a mass of 26.66 g
QUANTITIES IN CHEMISTRY
Symbol
n
m
M
N
NA
Quantity
Number of moles
mass
Molar mass
Number of entities
Avogadro’s constant
6.02 x 10 23
Unit
mol
g
g/mol
Atoms, ions, formula units, molecules, pillows…
----
SCH3U
Conversion Factors and Units
Through Avogadro’s number, you can easily convert from moles to any other unit
and vice versa, by using conversion factors. A conversion factor is a ratio that
describes how one unit is related to another unit.
Avogadro’s Constant
On a separate piece of paper complete the following problems:
1. The length of British Columbia’s coastline is 17 856 km. If you laid 6.022 x 1023 metre
sticks end to end along the coastline of BC, how many rows of metre sticks would you
have?
2. The area of Nunavut is 1 936 113 km2. Suppose that you had 6.022 x 1023 sheets of
pastry, each with the dimensions of 30cm x 30 cm. How many times could you cover
Nunavut completely with pastry?
3. If you drove for 6.022 x 1023 days at a speed of 100 km/h, how far would you travel?
4. If you spent $6.022 x 1023 at a rate of $1.00/second, how long in years you’re the
money last? Assume that every year has 365 days.
5. A typical human heart beats at an average of 60 times per minute. If you were
allotted a mole of heartbeats, how long, in years, could you expect to live? You may
assume each year has 365 days.
6. Calculate the number of atoms in 3.45 mol of iron, Fe.