IGCSE Chemistry titration calculations: 5 steps that score marks even when the final answer is wrong
Titration comes up in the Paper 4 calculations and the Paper 6 practical questions. This guide puts the method you must write in a table, lets you pick the right titres, then walks through the 5-step calculation with mistakes you switch on yourself, so you can see how many marks showing your working saves.
The short answer
Titration calculations always use the same 5 steps: mean titre → moles of the solution you know → mole ratio from the equation → concentration in mol/dm³ → g/dm³ if the question asks.
Cambridge mark schemes carry errors forward (ecf): get one step wrong, do the next one correctly from that number, and the next step still scores. But only if the working is written down.
If moles still feel shaky, read the mole explained and molar mass first.
The titration method, written in full
Describing a titration comes up on both Paper 4 and Paper 6. This table gives the 6 steps with an English sentence you can write in the exam. In this example, 25.0 cm³ of NaOH goes in a conical flask and H₂SO₄ is added from the burette.
Tap a row to highlight it
1. Prepare the burette
Write in the examRinse the burette with the acid, then fill it.
WhyWater left inside would dilute the acid
2. Measure the alkali
Write in the examUse a pipette to transfer 25.0 cm³ of the alkali into a conical flask.
WhyA pipette delivers a fixed volume more accurately than a cylinder
3. Add indicator
Write in the examAdd a few drops of methyl orange (or thymolphthalein).
WhyThe indicators the 0620 syllabus names
4. Titrate
Write in the examAdd acid from the burette while swirling; add it dropwise near the end-point.
WhyNear the end-point one drop changes the colour
5. End-point
Write in the examStop when the indicator changes colour: methyl orange yellow → orange; thymolphthalein blue → colourless.
WhyGive the colour before and after
6. Repeat
Write in the examRepeat until two titres are concordant; average them.
WhyMakes the result reliable
Which titres to average
The first run is the rough one, done fast to find the end-point roughly, so it usually overshoots. Average only the runs that agree closely (concordant). Pick them from the results below.
Tap the runs you would average
The 5-step calculation: add a mistake yourself
Choose a common mistake and watch the score. Then tick "write only the final answer" and compare: the same mistake scores 4 out of 5 with working, 0 without.
25.0 cm³ of aqueous sodium hydroxide is titrated with 0.0500 mol/dm³ sulfuric acid. H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O. Calculate the concentration of the sodium hydroxide in g/dm³. [5]
Add one mistake
- 1. Mean titre1
(20.10 + 20.00) ÷ 2 = 20.05 cm³
- 2. Moles of acid used1
n(H₂SO₄) = 0.0500 × 20.05 ÷ 1000 = 1.00 × 10⁻³ mol
- 3. Mole ratio from the equation1
n(NaOH) = 2 × n(H₂SO₄) = 2.01 × 10⁻³ mol
- 4. Concentration (mol/dm³)1
c(NaOH) = 2.01 × 10⁻³ ÷ 0.0250 = 0.0802 mol/dm³
- 5. Concentration (g/dm³) · Mr NaOH = 401
0.0802 × 40 = 3.21 g/dm³
Scores 5/5
All 5 steps, answer to 3 significant figures with units.
7 traps that cost marks
The usual traps in titration questions, and how to avoid each before you start writing.
Tap a row to highlight it
Averaging the rough run
What happensThe mean comes out too high
How to avoid itAverage only the concordant titres
Not converting cm³ to dm³
What happensThe answer is out by a factor of 1000
How to avoid itDivide by 1000 whenever a volume is in cm³
Ignoring the equation's ratio
What happensOut by 2 (or whatever the coefficient is)
How to avoid itCircle the coefficients before you start
Using the wrong volume
What happensDividing the alkali's moles by the acid's volume
How to avoid itLabel every line: n(NaOH), V(NaOH)
Giving mol/dm³ when asked for g/dm³
What happensThe last step is missing
How to avoid itReread the unit asked for, then multiply by Mr
Rounding mid-calculation
What happensThe final answer drifts
How to avoid itKeep full numbers; round once at the end (3 s.f.)
Recording a burette to 1 d.p.
What happensLoses the recording mark (Paper 6)
How to avoid itAlways 2 d.p., ending .00 or .05
Where Boom-Tutor helps
The course has an on-screen titration unit: the student adds the acid drop by drop, reads the burette, records the results in a table and carries on to the calculation, covering both the Paper 4 side and the Paper 6 side.
The self-learn IGCSE Chemistry course is ฿4,900, paid once, with access until the exam session. The platform is expected to open around December 2026.
Try: all 12 IGCSE Chemistry topics, interactive, on one page
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