What is a mole?
Ever wondered what a mole is? A mole seems complicated but
1 mole = 6.02214076 × 1023 atoms, molecules, compounds or ions
Mole explained in simple terms
Think of 1 mole as a way to group a very large amount of atoms/ ions/ molecules/ compounds similar to how we group people e.g. 1 class = 30 students , 1 football team (on the pitch) = 11 players.
Mole and its relationship to atomic mass unit of an element
If you look at the Periodic Table for an element, for example Iron (symbol Fe), you will notice the number 55.845 which is its atomic mass number; atomic mass number is g/mol units and that means that if you want 1 mole of Iron, you will need 55.845 g of it.
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Let’s take a look at another example which is Carbon-12. Carbon-12 (which has an atomic mass of 12 g/mol) helps to provide a concrete example of 1 mole because 12 grams of carbon-12 is equal to 1 mole of carbon atoms (think of coal as that is made mostly of carbon). Other substances will have different masses to make up 1 mole e.g. because a sodium atom has an atomic mass unit of 22.99 g/mol , you would need 22.99 g of sodium metal to make 1 mole of sodium atoms. Another example is calcium which has an atomic mass unit of 40.08 g/mol so you would need 40 g of calcium metal to make 1 mole of calcium atoms.
Fig. 4 – Picture showing 12g of carbon measured which is equivalent to 1 mole of carbon-12 atoms
Example of a past paper question involving moles
Let’s have a look at a past paper question example from PhysicsAndMathsTutor.com based on a GCSE AQA Chemistry past paper:
Below is an example Mark Scheme of how to solve it:
So in Step 1 of the mark scheme, we want to find out the number of molecules from 1 mole of carbon atoms, not from 70 carbon molecules so first step is to calculate 1÷70 = 0.0142857 moles.
Step 2:
if 1 mole = 6.02214076 × 1023 atoms
then
0.0142857 x 1 moles = 0.0142857 x 6.02214076 × 1023 atoms
0.0142857 moles = 8.6 x 1021 atoms