12.2 Acid–base titrations
- Syllabus
- 0620–2026–2027
- Topic
- 12.2
- Level
- —
Learning objectives
Carry out an acid–base titration
An acid–base titration finds the volume of one solution needed to react with a fixed volume of the other solution.
| Apparatus | Role in the titration |
|---|---|
| volumetric pipette | transfers one fixed, accurate volume into a conical flask |
| burette | delivers a measured, variable volume of the other solution |
| suitable indicator | shows when the end-point has been reached |
- Use the volumetric pipette to place a fixed volume of acid or alkali in a conical flask.
- Add a few drops of a suitable indicator.
- Fill the burette with the other solution and record the initial reading.
- Add solution from the burette while swirling the flask; add it dropwise near the colour change.
- Record the final burette reading when the end-point is reached. The volume delivered is final reading − initial reading.
The pipette measures the fixed volume placed in the flask; the burette measures the variable volume delivered. Do not swap their roles or estimate volume from markings on the conical flask.
Recognise the titration end-point
The end-point is identified by the indicator changing colour as the titrant is added.
Swirl after each addition and, near the end-point, add the solution from the burette one drop at a time. Stop at the first colour change that remains after swirling.
With methyl orange and alkali initially in the flask, the observed end-point can be the change from yellow to orange as acid is added.
Use a suitable acid–base indicator with a clear colour change over a narrow range. Universal indicator gives several gradual colour changes, so it does not show one sharp titration end-point clearly.
The colour direction depends on the indicator and on whether acid or alkali is added. The end-point is the observed indicator change, not simply the moment a chosen volume has been poured in.