Calculate the number of moles in 8.0 g of sodium hydroxide, NaOH. (Mr of NaOH = 40)
[2 marks]
Total for this question: 2
All calculations
Moles from mass
Quantitative chemistry
AQA 8462
ORIGINAL
Higher tier
n = m / Mr (moles = mass / relative formula mass)
n = m / Mr underpins nearly every calculation — get this automatic and the rest follow.
Board and spec code confirmed against AQA 8462 · registry checked 2026-07-17How this checking works
Work it, then mark it
Do each calculation on paper first, then reveal the mark scheme and tick the marks you actually earned — the same way you should mark past papers.
Q1
Do the calculation on paper first — then mark it.
Q2
Calculate the mass of 0.25 mol of calcium carbonate, CaCO3. (Mr of CaCO3 = 100)
[2 marks]
Total for this question: 2
Do the calculation on paper first — then mark it.
Where the marks get lost
- Using an Ar (atomic) instead of the Mr (formula) mass for a compound.
- Leaving the mass in a non-gram unit — convert to grams first.
- Rounding the moles too early and carrying the error into the next step.
Exam tip: Write the triangle n = m / Mr and cover the quantity you want. Keep 3+ significant figures in your working and only round the final answer.
Calculations are the most trainable marks in chemistry
They come up every paper and reward a clean method. Send me one you keep dropping marks on. Free intro call, then a free first lesson.
Stuck on moles from mass?
Everything here stays free. If moles from mass is where the marks keep going, I teach it one to one from the mark schemes. Free intro call, then a free first lesson.