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TitrationsOxford AQA IGCSE Chemistry: Revision notes

Section 1

What is a titration?

A titration is a technique used to measure the volumes of an acid and an alkali that react exactly with each other.

This specification only requires titrations using strong acids and strong alkalis — sulfuric acid, hydrochloric acid and nitric acid.

An indicator is used to show precisely when the reaction is complete (the end point), because the colour change signals that the acid and alkali have neutralised each other exactly.

Key termstitrationend pointindicator

Section 2

How is a titration carried out?

  1. Use a pipette to measure an accurate, fixed volume of one solution (e.g. the alkali) into a conical flask
  2. Add a few drops of a suitable indicator to the flask
  3. Fill a burette with the other solution (e.g. the acid) and record the initial reading
  4. Add the acid from the burette to the flask slowly, swirling the flask constantly
  5. Add the acid drop by drop as the colour starts to change, until the indicator just changes colour permanently (the end point)
  6. Record the final burette reading and calculate the volume of acid added (the titre)
  7. Repeat the titration until at least two concordant results (within 0.10 cm³ of each other) are obtained, then calculate a mean titre using only the concordant results
Exam tip

Examiners expect the method to mention swirling the flask, adding the solution drop by drop near the end point, and using a white tile under the flask to see the colour change clearly.

Section 3

How do you find the concentration of an unknown acid using titration?

Once the mean titre (volume) has been found:

  1. Calculate the moles of the solution with known concentration using n = c × V
  2. Use the mole ratio from the balanced equation to find the moles of the unknown solution
  3. Use c = n ÷ V (rearranged from n = c × V) with the volume of the unknown solution to calculate its concentration

This is the basis of the required practical: establishing the concentration of an unknown strong acid through titration with a strong base of known concentration.

Section 4

Why is repeating a titration important?

Repeating the titration and taking concordant results (titres agreeing within 0.10 cm³) reduces the effect of random errors, such as small differences in reading the burette or in judging exactly when the indicator changes colour.

Anomalous results (titres clearly different from the others) should be identified and not included in the mean titre calculation.

Must Know

  • Titration measures the volumes of acid and alkali that react exactly with each other
  • This specification uses only strong acids (sulfuric, hydrochloric, nitric) and strong alkalis
  • Method: pipette one solution into a flask with indicator, add the other from a burette until the end point, record the titre
  • Repeat until concordant results (within 0.10 cm³) are obtained and calculate a mean titre
  • The required practical finds the concentration of an unknown strong acid by titrating against a strong base of known concentration

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