Titrations
Get to grips with Titrations for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) required practical: titrate an acid against an alkali with an indicator to find the exact neutralisation volume.
Free downloads
These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Titration is used to find the exact volumes of acid and alkali that react together. This is a Triple-only required practical.
A pipette measures a precise volume of alkali into a conical flask, and a few drops of indicator are added. Acid is added from a burette, swirling constantly, until the indicator changes colour permanently — the end point. The volume delivered is the titre.
The indicator matters. Universal indicator is unsuitable because it gives a gradual range of colours rather than a sharp change. Phenolphthalein, which goes from pink to colourless, or methyl orange, which goes from yellow to red, give a sharp end point instead.
Revision notes
The method
Use a pipette to measure a precise volume of alkali into a conical flask and add a few drops of indicator.
Fill a burette with acid and record the starting reading. Add acid slowly, swirling constantly, until the indicator changes colour permanently. Record the final reading; the difference is the titre.
Choice of indicator
Universal indicator is unsuitable because it changes through a range of colours gradually, so no sharp end point can be seen.
Phenolphthalein changes from pink to colourless. Methyl orange changes from yellow to red. Both give a single sharp change.
Improving accuracy
Carry out a rough titration first, then repeat accurately, adding dropwise near the end point.
Repeat until two or more titres are concordant, meaning within 0.1 cm³ of each other, and calculate the mean of those. The rough titre is excluded.
Key points
- A pipette measures the alkali accurately.
- A burette delivers the acid.
- The titre is the volume of acid added.
- Universal indicator is unsuitable.
- Phenolphthalein goes pink to colourless.
- Concordant titres are within 0.1 cm³.
Worked examples
Example 1
Explain why universal indicator is not used in a titration. [2 marks]
Model answer
Universal indicator changes gradually through a range of colours (1 mark), so there is no sharp end point and the exact volume cannot be judged accurately (1 mark).
Example 2
Describe the colour change of phenolphthalein when acid is added to alkali. [1 mark]
Model answer
It changes from pink to colourless (1 mark).
Example 3
Explain why a rough titration is carried out first. [2 marks]
Model answer
The rough titration gives an approximate idea of the volume needed (1 mark), so in later titrations the acid can be added dropwise near the end point to find it accurately (1 mark).
Common mistakes
Using universal indicator.
It gives a gradual colour range, not the sharp end point a titration needs.
Including the rough titre in the mean.
Only concordant titres are averaged.
Measuring the alkali with a measuring cylinder.
A pipette is used because it is far more accurate.
Adding acid quickly throughout.
Add dropwise near the end point or the end point will be overshot.
Exam tips
- Name the specific apparatus — pipette and burette.
- Learn one indicator and its colour change precisely.
- Explain why universal indicator fails.
- Remember this is a Triple-only required practical.
Key terms
- Titration
- A technique to find reacting volumes accurately.
- Burette
- Apparatus delivering a measured, variable volume of liquid.
- End point
- The moment the indicator changes colour permanently.
- Concordant
- Titres within 0.1 cm³ of each other.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.