What this practice covers
These questions are drawn from past CIE 0620 Chemistry papers and filtered to relative masses of atoms and molecules. You answer, you find out immediately whether you were right, and you get the reasoning for the correct option and for each distractor. Wrong answers go to a mistakes locker so you can come back to exactly those.
Practice is free. You need an account only so your progress and your mistakes are still there next time.
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What examiners see students get wrong here
These are the errors that cost marks on relative masses of atoms and molecules, taken from our own topic notes. Read them before you practise and you will recognise the traps in the questions.
- Giving relative atomic mass or relative molecular mass a unit. Both are ratios.
- Calling the Mᵣ of an ionic compound a relative molecular mass.
- Ignoring the number outside a bracket, or applying it to only part of the group.
- Forgetting the water of crystallisation in a hydrated salt.
- Using the Mᵣ of one substance with the balancing number of another.
- Leaving out the balancing number altogether, so 2MgO is treated as 40 rather than 80.
- Adding masses of substances that are not in the same equation.
Revise it first
If any of the above is unfamiliar, work through the notes before practising: Relative masses of atoms and molecules revision notes.