The Mole
10 Science B, 2016
Avogadro’s constant
 1 mole is a very large number:
6.022 x 1023
 It is also known as Avogadro’s
constant.
A very large number
 If you had 6.022 x 1023 number
of soft drink cans they would
cover the surface of the earth to
a depth of over 300 km.
 If we were able to count atoms
at the rate of 10 million per
second, it would take about 2
billion years to count the atoms
in one mole.
Atomic mass
 The periodic table tells you the
atomic mass of atoms.
 This is expressed in Atomic Mass
Units (AMU).
 1 AMU is a very small unit and it is
impossible to weigh out 1 atom.
Molecular mass
 The mass of a molecule can be
calculated by adding up the masses
of its atoms:
 CO2:
12.011 + (2 x 15.999) = 44.009 AMU
The mole - What is it good for?
 1 mole (6.022 x 1023) of any pure
substance has a mass equal to its
atomic mass expressed in grams.
 So if you have 1 mole (6.022 x 1023)
carbon atoms they will weigh
exactly:
12.011 grams
Molar mass
 The molar mass is the mass (in
grams of 1 mole of atoms (or
molecules)
 The molar mass is exactly the same
as the atomic mass as in the
periodic table.
 Carbon’s molar mass is:
12.011 g/mol
Relationship between mass and molar mass
m=Mxn
This formula can be rearranged to
give the following:
m = mass (g)
M=m/n
M = molar mass (g/mol)
n = m /M
n = moles (mol)
Practice (converting mass to moles)
 How many moles are there in 6 g of carbon?
m = M x n, so n = m / M
n=?
m=6g
M = 12.011 g/mol
Solution: n = m / M
n = 6 g / 12.011 g/mol = 0.5 mol
Practice (converting moles to mass)
 What is the mass of 3.5 mol of CO2?
m=Mxn
m=?
M = 12.011 + (2 x 15.999) = 44.009 g/mol
n = 3.5 mol
Solution: m = M x n
m = 44.009 x 3.5 = 154 g
Practice (mass to number of atoms)
 How many atoms are there in 1 gram of aluminium?
n=m/M
m=1g
M = 26.982 g/mol
n = ? mol
Solution: n = m / M
n = 1 / 26.982 = 0.037 mol
Practice (mass to number of atoms)
 How many atoms are there in 1 gram of aluminium?
1 mol = 6.022 x 1023 atoms
0.037 mol = 6.022 x 1023 x 0.037 = 0.22 x 1023 number of Aluminium atoms