The Mole

When beginning to learn the important concepts and knowledge required to engage with the DP Curriculum it is important to have a basic understanding and experience of some of the ideas in each topic. At AIS the majority of students follow the iGCSE Coordinated Science curriculum as a precursor to studying DP chemistry and this site will use some of the objectives from the iGCSE to provide an area of prior learning - allowing those students who would like to refresh their knowledge or for new students to engage wth matter that has become prior to starting this course.

To this end students are expected to have a basic understanding of the C4 Stoichiometry unit

The Mole

Using balanced equations is incredibly important in chemistry, that being said chemists actually never react particles on the atomic scale - they want to use amounts of substances that they can see and measure and so we use the Mole.

But in order to understand the Mole we also need to understand how to calculate Relative Formula Mass

Relative Formula Mass = The Sum of the Relative Atomic Masses of each atom in a chemical formula

Example = Ethanoic Acid - CH3COOH

Contains 2 x C = 24

2 x O = 32

4 x H = 4

= 60

You can apply this to all chemical formula and therefore find the relative formula mass for any compound from the formula

Moles are not complicated! It is simply a label given to a number - think of it like a dozen - a dozen is always 12. Or Pi which is always 3.14159...

Moles help us to scale chemistry up to masses and amounts we can use in the real world.

It is based on the idea that although you can have the same mass of something - the actual number of items that make that mass up might be quite drastically different:

• Take 1 Tonne of Feathers vs. 1 Tonne of Gold

• Both of them are the same mass

• But the amount of Feathers will be far greater than the amount of Gold

This logic is applied to chemistry in the following ways

1 mole of a substance is EQUAL to it's Relative Formula Mass in Grams

So 1 Mole of Water (H2O) = 18 grams of Water Whereas 1 Mole of Glucose (C6H12O6) = 180 grams of Glucose

You could be forgiven if you thought that 180 grams of Glucose would have more particles than 18 grams of Water - But they have identical numbers of Particles

You can calculate Moles from Mass and Relative Formula Mass using the formula triangle below:

As an Example - we have 440g of CO2 - how many moles of CO2 is this?

The answer is:

• Moles = Mass/RFM

• = 440 / 44

• Moles = 10

So if the RFM in grams of elements/compounds is equal to the same number of particles - how many particles are there in one mole??

The answer is a number called Avogadro's Number.

Avogadro's Number = 6.02 × 10²³

Now let's apply the Mole to the following balanced equation:

Moles: 2 1 --> 2

Here we can see that if we react 2 moles of Sodium we Need 1 mole of Chlorine and this makes 2 moles of Sodium Chloride

This means that for every 2 particles of Sodium we need 1 particle of chlorine to react

If we had 20 moles of Sodium we would need 10 moles of Chlorine

If we had 40 moles of Chlorine we would need 80 moles of Sodium..

Hopefully you can see that the relationship between these is simply that we need double of one to react with the other

This also means we would Make double the particles of Sodium Chloride when compared to Chlorine AS THE NUMBER OF MOLES WHEN REACTING MASSES IS IRRESPECTIVE OF WHICH SIDE OF THE EQUATION THE COMPOUNDS ARE FOUND