Titration calculation
The boss level — find an unknown concentration from a titration by chaining three things you already know: moles = concentration × volume, the mole ratio from the balanced equation, and concentration = moles ÷ volume. Every full titration calculation is those three steps in a row.
How to do it — step by step
- Convert both volumes to dm³ (÷ 1000 if they're in cm³). Do this first, before anything else.
- moles of the solution you know = concentration × volume (dm³).
- Use the balanced equation's mole ratio to get moles of the unknown — check which way round it goes.
- concentration of the unknown = its moles ÷ its volume (dm³).
- Label every line ("moles NaOH = …", "moles HCl = …"). Examiners award method marks only when they can follow the working.
Worked examples — from real AQA papers
Where students lose marks — from the examiner reports
- Not converting cm³ to dm³. The most repeated comment across years — it produces moles 1000× too big ("moles acid = 5.4" made it into the 2025 report). Convert both volumes before touching anything else.
- Mole ratio the wrong way round — or missing. The 2025 report names both wrong answers (0.24 and 0.48 instead of 0.960). Write the ratio down from the balanced equation before you multiply.
- A jumble of unlabelled numbers. The 2020 report: students who "simply had a jumble of numbers, with no explanation" couldn't be given partial credit, and writing "m" instead of "n" for moles led them to confuse mass with moles. Label each line.
- Random arithmetic at Foundation. On the 2023 Foundation question, two-thirds scored nothing, with 160 a common answer from multiplying the wrong numbers together.
- Ignoring a significant-figures instruction. The 2023 Higher question paid a mark just for rounding 0.2627… to 0.263.
One more habit worth building: when a titration gives you several titre readings, use only the concordant ones (within 0.10 cm³ of each other) and take their mean — AQA mark schemes award a mark for that selection before the calculation even starts.
How often it comes up on AQA papers
From Science Street's database of real AQA questions:
| Paper | Marks | What you had to do |
|---|---|---|
| Chemistry Paper 1 Higher 2020 | 3 | Make the standard solution: mass of citric acid for 250 cm³ at 0.0500 mol/dm³ → 2.4 g |
| Chemistry Paper 1 Foundation 2023 | 3 | Mass of NaOH in 25.0 cm³ of a 4.00 g/dm³ solution → 0.1 g |
| Chemistry Paper 1 Higher 2023 | 5 | Full titration with a 1 : 2 ratio, answer to 3 s.f. → 0.263 mol/dm³ |
| Chemistry Paper 1 Higher 2025 | 4 | Full titration with a 2 : 1 ratio → 0.960 mol/dm³ |
The pattern: the full titration calculation is a Higher-tier, Chemistry Paper 1 staple — and more appear under Concentration (mol/dm³), where AQA asked essentially the same chain in 2019, 2020, 2021 and 2022. Foundation papers test the supporting steps instead: converting the volume and finding a mass from a concentration. If you're sitting Higher chemistry, expect a titration chain most years.
Now practise it — free
Science Street's Calculation Climb walks you from a worked example, through a guided step-by-step version, to questions you do yourself — with fresh examples every time and a built-in calculator and periodic table. No sign-up needed.
Practise Titration calculation on Science Street →