Titrations GCSE chemistry practicals measure an unknown acid or alkali concentration by slowly adding a standard solution from a burette until an indicator shows the reaction has just reached neutralisation. You record the volume added, repeat for concordant results, then use the mole equation to calculate the unknown concentration precisely.
What equipment do you need for a titration?
A titration uses precise glassware to measure liquid volumes accurately, and every piece in this required practical has a specific job:
- Burette — a long, graduated tube with a tap, used to add the solution of known concentration drop by drop, read to the nearest 0.05 cm³.
- Pipette and pipette filler — measures a fixed, accurate volume (commonly 25.0 cm³) of the solution being tested into the conical flask. A pipette is never filled by mouth.
- Conical flask — swirled throughout the titration; its narrow neck reduces splashing.
- White tile — placed under the flask so colour changes at the end point are easy to spot.
- Indicator — a few drops signal exactly when the reaction is complete.
How do you do a titration GCSE step by step?
- Rinse the apparatus. Rinse the burette with the solution it will hold, and the pipette with the solution it will measure, so residual water cannot dilute either solution.
- Fill the burette. Fill it above the 0.00 cm³ mark with the solution of known concentration, run a little through the tap to clear air bubbles, then record the initial reading.
- Measure the sample. Use the pipette and filler to transfer exactly 25.0 cm³ of the solution being tested into the conical flask, then add two or three drops of indicator.
- Run a rough titration. Add the burette solution while swirling continuously, watching for the first permanent colour change. Record this rough titre to see roughly how much volume is needed.
- Repeat accurately. Refill the burette. Add the solution quickly until close to the rough titre, then add it drop by drop near the end point, swirling constantly, until one drop causes a permanent colour change.
- Record the final reading and calculate the titre (final reading minus initial reading).
- Repeat until concordant. Continue accurate titrations until two titres agree within 0.10 cm³ of each other, then average the concordant results only — discard the rough titre and any outlier.
How do you read a burette correctly?
Read the burette at eye level, taking the measurement from the bottom of the meniscus, the curved liquid surface. Burettes are marked in 0.10 cm³ divisions, so results should be recorded to two decimal places, for example 23.45 cm³. Parallax error, caused by reading the scale from an angle instead of straight on, is one of the most common sources of inaccuracy in this titration method GCSE chemistry students meet, so always keep your eye level with the liquid.
Which indicator should you choose?
The indicator must give a sharp, easily-seen colour change exactly at the point of neutralisation.
| Indicator | Colour in acid | Colour in alkali | Typical use |
|---|---|---|---|
| Phenolphthalein | Colourless | Pink | Strong acid–strong alkali titrations |
| Methyl orange | Red | Yellow | Strong acid–weak alkali titrations |
Universal indicator is unsuitable for titrations because it changes colour gradually through a range of shades rather than sharply at one point, which makes the exact end point impossible to pinpoint.
Worked example: titration calculations GCSE
A student titrates 25.0 cm³ of sodium hydroxide solution against hydrochloric acid of concentration 0.100 mol/dm³. The mean concordant titre is 22.50 cm³. Calculate the concentration of the sodium hydroxide.
Step 1 — write the balanced equation: $$HCl + NaOH \rightarrow NaCl + H_2O$$
The mole ratio of HCl to NaOH is 1:1.
Step 2 — find moles of HCl used: $$\text{moles} = \text{concentration} \times \text{volume (dm}^3\text{)}$$ $$\text{moles HCl} = 0.100 \times \frac{22.50}{1000} = 0.00225 \text{ mol}$$
Step 3 — apply the mole ratio. Since the ratio is 1:1, moles of NaOH also equal 0.00225 mol.
Step 4 — find the concentration of NaOH: $$\text{concentration} = \frac{\text{moles}}{\text{volume (dm}^3\text{)}} = \frac{0.00225}{25.0 \div 1000} = 0.0900 \text{ mol/dm}^3$$
The sodium hydroxide solution has a concentration of 0.0900 mol/dm³.
What are the most common titration errors?
- Parallax error — reading the burette scale from an angle rather than eye level.
- Overshooting the end point by adding solution too quickly near the colour change, giving an inflated titre.
- Not swirling continuously, so the indicator reacts locally before the solution is fully mixed.
- Air bubbles in the burette tap at the start, giving a false initial reading.
- Averaging an anomalous result instead of discarding it — only titres within 0.10 cm³ of each other should be averaged.
Frequently asked questions
Why do you repeat a titration until the results are concordant?
A single titre could be affected by a misjudged end point or a reading error, so it cannot be trusted alone. Repeating the titration and only averaging results that agree within 0.10 cm³ (concordant results) cancels out small random errors and gives a mean titre that is far more reliable than any single measurement.
What is the difference between a rough and an accurate titration?
A rough titration is done quickly, adding solution steadily while swirling, purely to find the approximate volume needed for the colour to change. An accurate titration then adds solution quickly up to just before that rough volume, before slowing to drop-by-drop additions near the expected end point, so the true end point is caught precisely rather than overshot.
Why is a pipette used to measure the sample but a burette used to add the other solution?
A pipette measures one fixed, highly accurate volume, which is exactly what is needed for the known sample placed in the conical flask. A burette allows a variable volume to be added gradually and measured precisely at any point, which is essential because the volume needed to reach neutralisation is unknown until the titration is carried out.
Can titrations be used for reactions other than acid-base neutralisation?
Yes. While GCSE titrations focus on acid-base reactions monitored with an indicator, the same technique of adding one solution from a burette until a reaction is complete can be applied to other reaction types, such as redox titrations, where a colour change in the reacting solution itself signals the end point instead of a separate indicator.
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