Titrations (chemistry only) - AQA GCSE Chemistry Exam Questions

Practise 27 exam-style questions on Titrations (chemistry only) for AQA GCSE Chemistry. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.

27 questions
1–6 marks each
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20 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

2 marks

The diagram shows the apparatus used for a titration.

Name the piece of apparatus labelled A and give the purpose of B.

Diagram of a titration set-up. Label A points to the long, thin graduated glass tube held in the clamp; label B points to the white square the flask stands on.

Model answer

A is a burette. B is a white tile, which makes the colour change of the indicator easier to see so the end point can be judged accurately.

Explanation

The burette adds the solution in measured amounts and its scale allows readings to the nearest 0.05 cm³. The white tile gives a plain background so even a small colour change at the end point can be seen.

Mark scheme

1 mark
A: burette
do not accept pipette
1 mark
B (white tile) makes it easier to see the colour change of the indicator
allow so the end point can be seen clearly; naming it as a white tile alone does not score

Question 2

2 marks

A student washes a conical flask with distilled water and does not dry it before adding 25.0 cm³ of sodium hydroxide solution from a pipette for a titration.

Explain why the water left in the flask does not affect the titre.

Model answer

The water dilutes the sodium hydroxide, but the number of moles of sodium hydroxide in the flask is still the same. The volume of acid needed depends only on the number of moles of alkali it has to neutralise, so the titre does not change.

Explanation

Students often think any added water will spoil a titration. Water in the flask changes the concentration but not the amount of alkali, and it is the amount that decides how much acid reacts. Water in the burette or pipette is different, because it changes the amount delivered.

Mark scheme

1 mark
the number of moles of sodium hydroxide in the flask is unchanged
allow the amount of alkali stays the same
1 mark
the volume of acid needed depends only on the number of moles of alkali present
allow the same amount of acid is needed to neutralise it

Question 3

3 marks

A student titrates 25.0 cm³ of sodium hydroxide solution of unknown concentration with 0.100 mol/dm³ hydrochloric acid. In one titration the student adds too much acid and goes past the end point.

Explain the effect this has on the concentration of sodium hydroxide calculated from this titration.

Model answer

Overshooting the end point means the recorded titre is bigger than the volume really needed. The calculated number of moles of hydrochloric acid is therefore too large, and because moles of NaOH = moles of HCl, the calculated concentration of sodium hydroxide will be too high.

Explanation

Follow the error through the calculation: a larger volume of acid gives more moles of acid, which gives more moles of alkali in the same 25.0 cm³, so the concentration comes out too high. This is why acid is added drop by drop near the end point.

Mark scheme

1 mark
the titre recorded is larger than it should be
allow too much acid is recorded
1 mark
so the moles of hydrochloric acid calculated are too large
1 mark
so the calculated moles / concentration of sodium hydroxide is too high
do not award if the concentration is said to be too low

Question 4

4 marks

A student wrote this method for a titration to find the volume of hydrochloric acid that neutralises 25 cm³ of sodium hydroxide solution.

1. Rinse a burette with water, then fill it with hydrochloric acid.
2. Use a measuring cylinder to put 25 cm³ of sodium hydroxide solution into a beaker.
3. Add a few drops of universal indicator.
4. Add the acid from the burette until the indicator changes colour.
5. Record the volume of acid added.

Suggest four improvements to the student's method that would give more accurate results.

Model answer

Rinse the burette with the hydrochloric acid rather than water, so the acid is not diluted. Use a pipette rather than a measuring cylinder to measure the 25.0 cm³ of alkali accurately. Use a single indicator such as phenolphthalein, which has a sharp colour change, instead of universal indicator. Use a conical flask on a white tile, swirl it, add the acid drop by drop near the end point, and repeat until concordant titres are obtained so a mean can be calculated.

Explanation

Each improvement removes a source of error: diluted acid, an inaccurate volume of alkali, an unclear end point, poor mixing or a single unchecked result. Titration questions often ask you to spot weaknesses like these in a given method.

Mark scheme

1 mark
rinse the burette with the hydrochloric acid instead of water
max 4
1 mark
use a pipette instead of a measuring cylinder
1 mark
use a single indicator such as phenolphthalein or methyl orange instead of universal indicator
1 mark
use a conical flask (instead of a beaker) and swirl it while adding the acid
allow swirl the mixture
1 mark
add the acid drop by drop near the end point
allow do a rough titration first
1 mark
place the flask on a white tile
1 mark
record initial and final burette readings (read from the bottom of the meniscus at eye level)
1 mark
repeat until concordant results are obtained and calculate a mean

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