Acid–alkali titration — required practical

AQA GCSE Chemistry

Find the volume of acid needed to neutralise a known volume of alkali (or find an unknown concentration).

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Method

  1. Use a pipette to add a known volume of alkali to a conical flask; add a few drops of indicator.
  2. Fill a burette with the acid and record the start reading.
  3. Add acid slowly, swirling, until the indicator just changes colour (the end-point); record the final reading.
  4. Repeat to get concordant titres (within 0.10 cm³) and take a mean.

Results & analysis

Use concordant titres to find the mean titre. Then moles = concentration × volume; use the balanced equation ratio to find the unknown concentration.

Risk assessment

  • Acids and alkalis are irritant/corrosive — wear eye protection.

Improving accuracy & reliability

  • Read the burette at the bottom of the meniscus at eye level.
  • Add acid dropwise near the end-point; repeat for concordant results.
Exam tip: A single indicator with a sharp end-point (not universal indicator) gives an accurate colour change.

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