Fiducia TogetherMoles and calculations
The chemist's counting unit, and the calculations built on it.
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.
What it is
A mole is 6.02 × 10²³ particles. Moles = mass ÷ relative formula mass. Concentration = moles ÷ volume.
Where it applies
GCSE chemistry, mostly higher tier, and A Level throughout.
How it works
Moles connect a balanced equation to real masses. The equation gives the ratio in particles; moles convert that into grams you can weigh.
Percentage yield compares actual to theoretical yield; atom economy measures how much of the reactant mass ends up in the useful product.
How to use it in your work
Always start by balancing the equation. A mole calculation on an unbalanced equation is wrong from the first line.
Set the work out in steps — mass to moles, ratio, moles to mass — because method marks are awarded per step.
Watch units: concentration in mol/dm³ needs volume in dm³, and 1000 cm³ = 1 dm³.
Where to get help
Your teacher, your board's specification for the depth required at your tier, and Bitesize for the diagrams. The subject song runs the topics in order.
Revise this with a song
These are ours. We write revision songs because a lot of people remember a tune when they cannot remember a page, and because revising out loud in the kitchen beats staring at a highlighter.
- The Chemistry Song The GCSE chemistry specification, set to music.
Where to read more
Last reviewed 2026-08-28 by Fiducia Together · Next review due 2027-08-28
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.