Skip to content

4.11 Titrations

How to carry out an accurate acid-alkali titration using a pipette, burette and indicator, how to read a burette, and how to identify concordant titres and calculate a mean titre.

AQA Edexcel OCR 2 min read

What a titration does

Key terms

  • Titration: a method used to find the exact volume of one solution that reacts with a known volume of another.
  • End point: the point at which the indicator changes colour, showing the reaction is just complete.
  • Titre: the volume of solution added from the burette to reach the end point.

This is AQA required practical 2 and Edexcel core practical 5.9C, and it is one of OCR's practical activities. The calculations are in the lesson on concentrations in mol/dm3.

A burette of acid clamped above a conical flask of alkali and indicator on a white tile, a 25.0 cm3 pipette with a filler, and a results table with rough and accurate titres and the mean of the concordant results
A burette of acid clamped above a conical flask of alkali and indicator on a white tile, a 25.0 cm3 pipette with a filler, and a results table with rough and accurate titres and the mean of the concordant results

Method

  1. Rinse a pipette with the alkali, then use a pipette filler to transfer exactly 25.0 cm3 of alkali into a conical flask.
  2. Add a few drops of an indicator such as phenolphthalein or methyl orange.
  3. Rinse a burette with the acid, then fill it. Record the initial reading at eye level, from the bottom of the meniscus.
  4. Stand the flask on a white tile so the colour change is easy to see.
  5. Add acid from the burette, swirling the flask. Near the end point, add the acid drop by drop.
  6. Stop when the indicator just changes colour permanently. Record the final reading.
  7. Do a quick rough titration first, then repeat accurately until you have concordant results (titres within 0.10 cm3 of each other).

Why each piece of equipment

Equipment
EquipmentReason
Pipettemeasures a fixed volume very accurately
Burettemeasures the variable volume added, to 0.05 cm3
White tilemakes the colour change easy to see
Single indicatorsudden, clear colour change at the end point

Universal indicator is not used, because it changes colour gradually through many colours, so the end point is not clear.

Calculating the mean titre

Ignore the rough titre. Average only the concordant titres.

Test yourself on this lesson

5 exam questions · 7 marks · with mark schemes and model answers

Start questions

Found a mistake?