MOLE
A mole in Chemistry is NOT:
 An informer / spy
 Dark spot on Cindy Crawford’s upper lip
 Rodent that burrows in the ground
 A tunneling machine
 Wave break
 Spicy Mexican sauce
We’ll see that a mole is a convenient measuring tool. A mole is a wonderful
concept.
Baseballs
Pineapples
Calculators
Planets
Bakers’ Dozen
Pair
Dozen
2 baseballs
12 baseballs 13 baseballs
2
Pineapples
2
Calculators
2 Planets
12
Pineapples
12
Calculators
12 Planets
13 Pineapples
13 Calculators
13 Planets
In chemistry we use another “amount” thingy called a mole.
Mole = mol = 6.022  1023 “particles”
Baseballs
Pineapples
Calculators
Planets
mole
6.022  1023 baseballs
6.022  1023 Pineapples
6.022  1023 Calculators
6.022  1023 Planets
Ream
500
baseballs
500
Pineapples
500
Calculators
500 Planets
Just as
1 doz eggs = 12 eggs
We can also say
1 mol of eggs = 6.022  1023 eggs
A mole is a “Number”
1 mol of H = 6.022  1023 atoms of H
1 mol of O = 6.022  1023 atoms of O
1 mol of Al = 6.022  1023 atoms of Al
1 mol of Cr = 6.022  1023 atoms of Cr
We use moles in chemistry as a way to COUNT what we have.
However,
In chemistry, the mol is more then just a number.
The mole concept was developed alongside atomic mass:
1 mol  amu = 1.00 g
1amu 
1
mass
12
C  1.661  10 24 g
12
Why use 1/12 mass of a 12C and call it an “amu”----12C makes a nice standard---- 1
amu is equal to the average mass of a proton and a neutron (electrons are relatively
mass-less compared to the proton or neutron so we ignore the mass of an
electron)…so if you add 12 amu’s you get the mass of a carbon (which is equal to
6 protons and 6 neutrons…that is where the 12 amu’s comes from…6 protons plus
6 neutrons)….16 amu’s you get the mass of an oxygen atom (8 protons plus 8
neutrons is 16)….52 amu’s gives you the mass of a chromium atom (26 protons
plus 26 neutrons equals 52). The entire periodic table is based on it’s relative mass
as compared to 12C.
1 mol  amu = 1.00 g
mole = a big number AND mass
Proof:
1 mol = 6.022  1023
amu = 1.661  10-24 g
1 mol amu = (6.022  1023)  (1.661  10-24g) = 1.00 g
Therefore, a mole of an element = elements amu expressed in g------More Simply:
1 mol of H = 1 amu = 1 g H
1 mol of O = 16 amu = 16 g O
1 mol of Al = 27 amu = 27 g Al
1 mol of Cr = 52 amu = 52 g Cr
“Key-Point”-----mol in chemistry is a function of numbers to mass….Beauty of a
mol is…..by weighing something you know how many atoms you have. This is
the only way chemists have to relate numbers (number of atoms of one
compound) to mass (how much of the other atoms do I need in the reaction) in
ALL CHEMICAL EQUATIONS.
All the information we need is conveniently laid out on the Periodic Table.
Question what weighs more a mole of H or a mole of Cr? Which has more atoms?
MOLECULAR WEIGHT & FORMULA WEIGHT
Note: that Molecular Weight and Molecular Mass mean the same thing (as you
may remember we said that mass  weight…that weight had gravity associated
with it…see Chapter 1 subheading Matter). In fact Formula Weight and Formula
Mass mean the same thing. Chemist have never changed these terms to reflect
what they should mean. I use mw = molecular weight.
A mole of Fe = Fe 55.85 amu = Fe 55.85 g
AMU -VS- MW
amu is replaced with mw to indicate we are speaking in terms of molecules. AMU
refers to elements and MW refers to molecules or collection of atoms (i.e.
collection of AMU’s).
55.85 g Fe
1moleFe 
55.85amuFe
g
 55.85
 55.85amu
mol
FeSO4 is a molecule containing iron. A molecule is recorded as MW, hence
1moleFeSO4 
151.90 g FeSO4
151.90mw FeSO4