Chemistry required practicals

Acid-alkali titration

AQA 4.4 · RP2

GCSE Chemistry (8462) · Required practical 2 — method, variables, the marks examiners report students losing.

Verified against AQA 8462 (2026 spec)

Find the volume of acid needed to neutralise a known volume of alkali, and use it to work out an unknown concentration.

Apparatus

  • Burette (0.1 cm3 graduations, read to the nearest 0.05 cm3)
  • 25 cm3 pipette and pipette filler
  • Conical flask and white tile
  • Dilute acid and alkali of known volume
  • Indicator (methyl orange or phenolphthalein)

Method

  1. 1Use the pipette to measure exactly 25.0 cm3 of alkali into the conical flask; add a few drops of indicator.
  2. 2Fill the burette with the acid and record the initial reading (bottom of the meniscus, at eye level).
  3. 3Stand the flask on a white tile; add acid while swirling, until the indicator just changes colour permanently (the end-point).
  4. 4Record the final burette reading; the difference is the titre.
  5. 5Do a rough (trial) titration first, then repeat until you have concordant titres (within 0.10 cm3).
  6. 6Calculate the mean of the concordant titres, ignoring the rough.

Results & processing

  • Record all readings to 0.05 cm3 in a results table.
  • Mean only the concordant titres; use moles = concentration x volume to find the unknown concentration.

Where students lose marks

Including the rough (trial) titre in the mean.

Fix: Only average concordant titres (within 0.10 cm3 of each other); the rough is just a guide.

Reading the burette from the top, or not at eye level.

Fix: Read the bottom of the meniscus at eye level, to the nearest 0.05 cm3, to avoid a parallax error.

Overshooting the end-point.

Fix: Add the acid dropwise near the end-point, swirling constantly, so you stop at the first permanent colour change.

Improve the method

  • Repeat until titres are concordant, then mean them.
  • Use a white tile under the flask to judge the colour change precisely.

Try it — exam-style

Medium
2 marks
ORIGINAL

A student's titres are 24.10, 25.60, 24.15 and 24.05 cm3. State which values should be used for the mean titre, and calculate the mean.

Easy
2 marks
ORIGINAL

Explain why the alkali is measured with a pipette but the acid is added from a burette.

Questions are written in the style of past AQA papers — never copied from them.

Drill it properly

Moles & concentration trainer

The moles = c x v arithmetic every titration calculation needs.

AQA GCSE Chemistry flashcards

Titration technique and the concordant-titre rule, drilled.

Stuck on acid-alkali titration?

Titration marks are lost on technique and the mean-titre rule, not the chemistry — I drill both until they're automatic, and your first lesson is free.

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