AQA GCSE Chemistry · Chemical ChangesTriple only
Titration required practical
Find the volumes of a strong acid and a strong alkali that react exactly, by titration.
You add acid from a burette to a measured volume of alkali until the indicator just changes colour. Repeating until results agree gives an accurate titre, which you can use to find a concentration.
This one is only on the separate Chemistry GCSE, so it won’t come up in Combined Science.
Equipment
- Burette, clamp stand and white tile
- Volumetric pipette (25.0 cm³) and pipette filler
- Conical flask and small funnel
- Dilute hydrochloric acid and sodium hydroxide solution (0.100 mol/dm³)
- Indicator, e.g. phenolphthalein or methyl orange
Variables
- Independent you change
- Not a fair-test practical: you repeat the same titration
- Dependent you measure
- Volume of acid needed to neutralise the alkali (the titre)
- Control you keep the same
- Same volume of alkali (25.0 cm³)
- Same indicator and number of drops
- Same concentration of acid and alkali
Method
- 1
Use a pipette and filler to put 25.0 cm³ of sodium hydroxide into a conical flask. Add a few drops of indicator.
- 2
Rinse and fill the burette with hydrochloric acid, using a funnel. Remove the funnel and record the start reading at eye level.
- 3
Put the flask on a white tile under the burette. Add acid while swirling the flask.
- 4
Do a rough run first. Then repeat, adding the acid drop by drop near the end point, until the colour just changes.
- 5
Record the end reading and work out the titre (end − start).
- 6
Repeat until you have concordant results (within 0.10 cm³) and calculate their mean.
Worked example
25.0 cm³ of 0.100 mol/dm³ NaOH titrated with HCl, using phenolphthalein (pink → colourless).
| Run | Start (cm³) | End (cm³) | Titre (cm³) |
|---|---|---|---|
| Rough | 0.00 | 24.90 | 24.90 |
| 1 | 0.50 | 24.85 | 24.35 |
| 2 | 0.20 | 24.60 | 24.40 |
| 3 | 1.00 | 25.35 | 24.35 |
Working
Concordant titres: 24.35, 24.40, 24.35 → mean = 73.10 ÷ 3 = 24.37 cm³
Moles of NaOH = 0.100 × (25.0 ÷ 1000) = 0.00250 mol
HCl + NaOH → NaCl + H₂O, so moles of HCl = 0.00250 mol
Concentration of HCl = 0.00250 ÷ (24.37 ÷ 1000) = 0.103 mol/dm³
Conclusion
It takes a mean of 24.37 cm³ of acid to neutralise 25.0 cm³ of the alkali, so the hydrochloric acid has a concentration of 0.103 mol/dm³. The rough run is left out of the mean because it overshoots the end point.
Risks
- Acid and alkali irritate skin and eyesWear eye protection; sodium hydroxide is especially harmful to eyes.
- Filling the burette above eye levelFill it below eye level, on the bench or with the burette lowered.
- Pipetting by mouthAlways use a pipette filler.
Common mistakes
- Including the rough titre in the mean. Only use concordant results.
- Leaving the funnel in the burette. Drops can fall from it and change the reading.
- Reading the burette from the top of the meniscus or at an angle. Read the bottom of the meniscus at eye level.
Better results
- Add acid drop by drop near the end point and swirl after each drop.
- Rinse the burette with the acid (not water) before filling, so the acid isn’t diluted.
- Use a white tile so the colour change is easier to see.
Launching November 2026
7 exam questions on this practical.
Practise the method, the variables, the maths and what the results mean, then revise the Chemical Changes flashcards. It opens to students soon: join the waitlist and we’ll email you once, when it does.