AQA GCSE Chemistry: Use Moles in Calculations (Higher Tier)

Welcome to this deck on using moles in calculations. This is a Higher Tier topic in GCSE Chemistry. The mole is the chemist's unit for counting atoms, molecules, and ions. It allows us to scale up from the atomic level to the masses we can actually measure in a lab. In this deck, you'll learn what a mole is, how to calculate moles from a given mass, and how to use balanced equations to work out how much product a reaction will make. We'll also cover how to identify the limiting reactant, which is the chemical that runs out first and stops a reaction.

So, what exactly is a mole? Just like a 'dozen' means twelve of something, a 'mole' means a specific, very large number of particles. This number is called Avogadro's constant, and its value is 6.02 times 10 to the power of 23. So, one mole of carbon contains that many carbon atoms, and one mole of water contains that many water molecules. It's a huge number because atoms themselves are incredibly small.

For your exam, you won't usually need to use Avogadro's constant in calculations. Instead, you'll use a fundamental equation that links the mass of a substance, its relative formula mass, or Mr, and the number of moles. The equation is: mass equals moles multiplied by the relative formula mass. You'll need to be able to rearrange this to find any of the three values.