A mole is a unit of quantity.
A mole is 6.02 x 1023 things.
6.02 x 1023 is known as Avogadro’s constant (NA)
÷ 6.02 x 1023
× 6.02 x 1023
molecule of water
How many molecules in
2000 cm3 of water?
6.7 x 1025 molecules
6.7 x 1025 molecules is not a manageable
We count eggs by the dozen
We measure long periods of time in
We measure long distances in our
universe using light years.
There are many ways of measuring large
quantities that utilize large units. The mole
is one such unit.
The mole is the SI unit for chemical
quantity used to count the particles in a
sample of pure substance.
One mole = 6.02x1023 particles.
“One mole of anything = 6.02x1023 units of that thing”
molecules of water
in 2000 cm3?
6.7 x 1025 molecules
Or 111 mol meaning 111 moles of water
molecules. This is a much more manageable
How many atoms are in 0.065 mol of copper? 3.9 x 1022
How many molecules are in 0.065 mol of CO2? 3.9 x 1022
How many formula units are in 0.065 mol of NaCl? 3.9 x 1022
How many moles is 9.03 x 1023 atoms of copper? 1.5
How many moles is 9.03 x 1023 molecules of CO2? 1.5
How many moles is 9.03 x 1023 formula units of NaCl? 1.5
How many oxygen atoms are in 1.4 x 10-7 mol of oxygen gas (O2)?
(1.4 x 10-7) × NA = 8.428 x 1016 molecules of O2
2 atoms of oxygen per molecule so
final answer = 1.7 x 1017 atoms of oxygen (2 SF)
Given 1.76 x 1012 molecules of O2, how many moles of iron III oxide
(Fe2O3) can be assembled?
1.76 10 molecules O 2 atoms/molecule
6.02 10 3 atoms/molecule
1.95 10 moles Fe O
What are chemical formulae?
● short-hand notation
● tells us the types of elements in a compound
● gives the number of atoms of each type of
element in one molecule of the compound
H2SO4 sulphuric acid
4 atoms of oxygen
1 atom of sulfur
2 atoms of hydrogen
1 molecule of H2SO4
How many atoms?
Mg(NO3)2 magnesium nitrate
Cu(SO4)2●5 H2Ocopper II sulfate
Relative Formula/Molecular Mass (MR)
The average relative atomic mass (AR) for each element is
noted on the Periodic Table. For example AR for copper
is 63.55. Relative masses are based on 1/12th the mass of
a 12C atom.
The relative formula mass is the total mass of the atoms in
one molecule of a particular compound. For example H2SO4:
Hydrogen 2 atoms × 1.01 = 2.02
Sulfur 1 atom × 32.07 = 32.07
Oxygen 4 atoms × 16.00 = 64.00
Mass and the Mole: Why 6.02×1023?
1 atom of sulfur AR = 32.07 = 5.326×10-23 grams
1 mole of sulfur = 6.02×1023 atoms = 32.07 grams
1 mole = 6.02×1023 was chosen because this was then
number of carbon-12 atoms that has a mass of 12
Aluminum AR = 26.98
gram atomic mass = 26.98 g mol-1
Carbon dioxide (CO2) MR = 44.00
gram molecular mass = 44.00 g mol-1
Sodium chloride (NaCl)
gram atomic mass
gram molecular mass
gram formula mass
MR = 58.44
gram formula mass = 58.44 g mol-1
We weigh chemical quantities in grams. The molar
mass value for a substance allows us to determine the
number of moles from a measured mass.
Consider 5.68 g of MgCl2
Molar mass of MgCl2 = 95.21 g mol-1
92.51 g mol
0.0597 moles of MgCl2 molecules or….
0.0597 moles of Mg atoms or….
0.119 moles of Cl atoms
Atoms combine to form compounds in chemical
These combinations occur in whole number
ratios (chemical formulae) – it is the number of
each type of atom that is important (we count
numbers with MOLES)
We measure chemical quantities by MASS.
Molar mass is a very important aspect of
quantitative chemistry because it relates MASS
to MOLES (number of atoms)
÷ 6.02 x 10 Number of 23
× 6.02 x 1023
× molar mass
÷ molar mass
How many mole are in 45.0 g of water? 2.50 mol
What is the mass of 1.75 mol of CO2? 77.0 g
How many moles of oxygen atoms are in
300 g of CaCO3?
What is the mass of 9.03 x 1023 atoms of copper? 95.3 g
106 g of glucose (C6H12O6) is how many moles? 0.589 mol
What is the mass of the oxygen atoms in the previous