Why is "Forgetting to convert cm³ to dm³" a common mistake in Acid–base titrations (New)?

Why it happens: Skipping the conversion. How to avoid it: Divide by 1000: 25.0\,cm^3 = 0.0250\,dm^3. Source: 0620/42 — recurring

Why is "Using 1:1 ratio when equation has different ratio" a common mistake in Acid–base titrations (New)?

Why it happens: Default assumption. How to avoid it: Read the balanced equation. e.g. 2NaOH + H_2SO_4 has 2:1 ratio.

Why is "Including the rough titre in the mean" a common mistake in Acid–base titrations (New)?

Why it happens: Treating all titres equally. How to avoid it: Use only CONCORDANT titres for the mean. Discard the rough.

Experimental Techniques and Chemical AnalysisCambridge IGCSE Chemistry 0620 Extended

Acid–base titrations (New)

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Acid-Base Titrations — Cambridge IGCSE 0620 Chemistry Extended (2026)

Pipette + burette + indicator. The standard procedure to find the exact concentration of an unknown solution. Plus the calculation: $n = c V$ , mole ratio, repeat.

What you’ll learn

Mapped to the Cambridge IGCSE 0620 syllabus (2026-2028).

14.2 — Describe the procedure for an acid-base titration.
14.2 — Calculate the concentration of an unknown solution from titration data.

Titration procedure

Pipette alkali → add indicator → titrate with acid from burette → stop at end-point → repeat for concordance.

Step-by-step.

RINSE the pipette with the alkali (so any residue inside doesn't dilute the volume you take). Rinse the burette with the acid.
PIPETTE a known volume of alkali (e.g. $25.0\,\text{cm}^{3}$ ) into a CLEAN conical flask. Add a few drops of INDICATOR.
FILL the burette with acid above the $0$ mark; tap to remove air bubbles; release acid until the level is at $0$ (or some recorded starting volume). Record initial reading.
TITRATE: SLOWLY release acid from the burette into the conical flask, swirling continuously to mix. Watch for the indicator colour change.
STOP at the end-point (first permanent colour change). Record final burette reading.

Acid is run from the burette into a measured volume of alkali until the indicator changes colour.

TITRE = final − initial reading.
REPEAT the titration. Get at least three CONCORDANT titres (within $0.10\,\text{cm}^{3}$ of each other). Average the concordant titres for the final value.

Why repeat? First titration is rough (you find the approximate end-point). Second and third are precise — drop-by-drop near the end-point.

Cambridge tip. Cambridge often awards marks for: pipette use, indicator addition, swirling during titration, drop-by-drop near end-point, repeating.

Pipette the alkali; record volume.
Add indicator.
Burette in acid; record initial reading.
Titrate slowly; swirl; watch for colour change.
End-point: first permanent change.
Repeat for concordance ( $\pm 0.10\,\text{cm}^{3}$ ).

Choosing an indicator

Methyl orange for strong acid + strong/weak base. Phenolphthalein for strong base + strong/weak acid. Universal: rough use only.

Indicators change colour over a range of pH.

Indicator	Acidic	Neutral	Alkaline	pH range of change
Methyl orange	Red	Orange	Yellow	$\sim 3-4$
Phenolphthalein	Colourless	(still colourless)	Pink	$\sim 8-10$
Universal indicator	Red → green → purple	over pH 1-14		wide

Choosing for titration. Cambridge is broadly:

Strong acid + strong base: any indicator works (large pH jump at end-point covers all ranges).
Strong acid + weak base (e.g. HCl + NH₃): use METHYL ORANGE (end-point in acidic range).
Weak acid + strong base (e.g. ethanoic acid + NaOH): use PHENOLPHTHALEIN (end-point in alkaline range).
Weak acid + weak base: titration not reliable (no sharp colour change).

Universal indicator is NOT used in titrations — colour change is gradual, not sharp. Used for measuring unknown pH only.

End-point colour change examples.

Phenolphthalein in NaOH (pink) → as HCl is added, becomes colourless at end-point.
Methyl orange in NaOH (yellow) → red at end-point.

Cambridge tip. Cambridge often asks "which indicator is suitable?" Answer with the indicator AND the colour change. Don't just say "phenolphthalein" — say "phenolphthalein turns from pink to colourless".

Methyl orange: red → yellow (acidic to alkaline).
Phenolphthalein: colourless → pink (acidic to alkaline).
Strong-strong: any indicator.
Strong acid + weak base: methyl orange.
Weak acid + strong base: phenolphthalein.
Universal indicator: NOT suitable for titration.

Titration calculations

Use $n = c V$ for both, balance the equation, apply mole ratio.

Standard sequence.

Write the balanced equation.
Work out moles of the KNOWN reagent: $n = c \times V$ (V in dm³).
Use the mole RATIO from the equation to find moles of the OTHER reagent.
Use the volume of the OTHER reagent to find its concentration: $c = n/V$ .

Every titration calculation follows the same four steps — always start with the balanced equation.

Worked. $25.0\,\text{cm}^{3}$ of NaOH(aq) is neutralised by $20.0\,\text{cm}^{3}$ of $0.10\,\text{mol/dm}^{3}$ HCl. Find concentration of NaOH.

Step 1. Equation: $\text{NaOH} + \text{HCl} \to \text{NaCl} + \text{H}_{2}\text{O}$ .

Step 2. Moles of HCl: $n = c V = 0.10 \times (20.0/1000) = 0.002\,\text{mol}$ .

Step 3. Mole ratio NaOH : HCl = $1 : 1$ . So moles of NaOH = $0.002\,\text{mol}$ .

Step 4. Concentration of NaOH: $c = n/V = 0.002 / (25.0/1000) = 0.080\,\text{mol/dm}^{3}$ .

Worked (different ratio). $25.0\,\text{cm}^{3}$ of NaOH(aq) neutralised by $15.0\,\text{cm}^{3}$ of $0.10\,\text{mol/dm}^{3}$ H₂SO₄.

Step 1. $\text{H}_{2}\text{SO}_{4} + 2\text{NaOH} \to \text{Na}_{2}\text{SO}_{4} + 2\text{H}_{2}\text{O}$ .

Step 2. Moles H₂SO₄: $0.10 \times 0.0150 = 0.00150\,\text{mol}$ .

Step 3. Ratio H₂SO₄ : NaOH = $1 : 2$ . Moles of NaOH: $2 \times 0.00150 = 0.00300\,\text{mol}$ .

Step 4. Concentration of NaOH: $0.00300 / 0.0250 = 0.120\,\text{mol/dm}^{3}$ .

Cambridge tip. Watch out for stoichiometric ratios (especially 1:2 with H₂SO₄ or H₃PO₄). Always start with the balanced equation.

Standard 4 steps: equation, $n$ known, ratio, $c$ unknown.
$n = c V$ , V in dm³.
Use balanced equation for ratio.
Watch for 1:2 stoichiometry (H₂SO₄, etc.).

How it’s examined

Titrations appear every Paper 4 (8-12 marks) and Paper 6 (procedural). Examiner reports flag mole-ratio mistakes (forgetting the 1:2 of H₂SO₄) and using $\text{cm}^{3}$ instead of dm³ in $n = c V$ .

Sources: Cambridge IGCSE Chemistry 0620 syllabus 2026-2028 (14.2); 0620/42 Oct/Nov 2024 — Q27 (titration calculation); 0620 Examiner Reports 2022-2024. Last reviewed 2026-05-07.

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Step-by-step worked examples — Acid–base titrations (New)

Step-by-step solutions to past-paper-style questions on acid–base titrations (new), written exactly the way a tutor would explain them at the board.

1Standard titration procedure
Extended• Adapted from 0620/62 May/Jun 2024 Q5• procedure
Question
List the main steps for finding the concentration of a NaOH solution by titration with $0.100\,\text{mol/dm}^{3}$ HCl.
Step-by-step solution
1. Step 1
  Pipette $25.0\,\text{cm}^{3}$ of NaOH into a conical flask. Add a few drops of indicator (e.g. methyl orange).
2. Step 2
  Fill burette with HCl. Record initial reading.
3. Step 3
  Add HCl from the burette while swirling. Stop when indicator changes colour. Record final reading.
4. Step 4
  Repeat to obtain CONCORDANT titres (within $0.1\,\text{cm}^{3}$ ). Take the mean.
Answer
Pipette base + indicator; titrate with acid from burette; record titre; repeat to concordance; mean.
2Calculate concentration
Extended• calculation
Question
$25.0\,\text{cm}^{3}$ of NaOH is exactly neutralised by $20.0\,\text{cm}^{3}$ of $0.100\,\text{mol/dm}^{3}$ HCl. Find the concentration of NaOH. $\text{NaOH} + \text{HCl} \to \text{NaCl} + \text{H}_{2}\text{O}$ .
Step-by-step solution
1. Step 1
  Moles of HCl.
  $n_{\text{HCl}} = 0.100 \times 0.0200 = 0.00200$
2. Step 2
  1:1 → moles NaOH = 0.00200.
3. Step 3
  Concentration.
  $c = \dfrac{0.00200}{0.0250} = 0.0800\,\text{mol/dm}^{3}$
Answer
$0.0800\,\text{mol/dm}^{3}$
3Choose an indicator
Extended• indicator
Question
Suggest an indicator for: (a) strong acid + strong base, (b) strong acid + weak base, (c) weak acid + strong base.
Step-by-step solution
1. Step 1
  (a) Methyl orange or phenolphthalein both work.
2. Step 2
  (b) Methyl orange (changes in acidic range).
3. Step 3
  (c) Phenolphthalein (changes in alkaline range).
Answer
(a) Either. (b) Methyl orange. (c) Phenolphthalein.

Key Formulae — Acid–base titrations (New)

The formulae you need to memorise for acid–base titrations (new) on the Cambridge IGCSE 0620 paper, with every variable defined in plain English and a note on when to use it.

Titration calculation
$n = c V \to \text{ratio} \to c_{\text{unknown}} = \dfrac{n_{\text{unknown}}}{V_{\text{unknown}}}$
When to use
Standard procedure for any titration calculation.

Key Definitions and Keywords — Acid–base titrations (New)

Definitions to memorise and the exact keywords mark schemes credit for acid–base titrations (new) answers — sharpened from recent examiner reports for the 2026 0620 sitting.

Titration
Examiner keyword
Volumetric method for determining the concentration of an unknown solution by reaction with a known one.
End-point
Examiner keyword
The volume at which the indicator just changes colour.
Concordant titres
Examiner keyword
Two or more titres that differ by no more than $0.1\,\text{cm}^{3}$ .

Common Mistakes and Misconceptions — Acid–base titrations (New)

The traps other students keep falling into on acid–base titrations (new) questions — taken from recent Cambridge IGCSE 0620 examiner reports and mark schemes — and how to avoid them.

✕Forgetting to convert cm³ to dm³
0620/42 — recurring
Why it happens
Skipping the conversion.
How to avoid it
Divide by 1000: $25.0\,\text{cm}^{3} = 0.0250\,\text{dm}^{3}$ .
✕Using 1:1 ratio when equation has different ratio
Why it happens
Default assumption.
How to avoid it
Read the balanced equation. e.g. $2\text{NaOH} + \text{H}_{2}\text{SO}_{4}$ has 2:1 ratio.
✕Including the rough titre in the mean
Why it happens
Treating all titres equally.
How to avoid it
Use only CONCORDANT titres for the mean. Discard the rough.

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

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Acid–base titrations (New)

Short Study Notes in the form of Slides

Short Study Notes — Acid–base titrations (New)

Detailed Notes

What you’ll learn

How it’s examined

1Standard titration procedure

2Calculate concentration

3Choose an indicator

Titration calculation

Titration

End-point

Concordant titres

✕Forgetting to convert cm³ to dm³

✕Using 1:1 ratio when equation has different ratio

✕Including the rough titre in the mean

Practice questions

Past paper style quiz

Assess your understanding

Video lesson