AQA GCSE Chemistry (8462), Higher tier · Chemical changes › Reactions of acids
Practise Strong and weak acids. 12 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Acids can be described as strong or weak. Give one example of a weak acid.
ethanoic acid (or citric acid or carbonic acid)
Complete the sentence. A weak acid is only .................... ionised in aqueous solution.
partially
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Acids can be strong or weak.
(a) Which acid is a weak acid? Tick (✓) one box.[1]
Hydrochloric acid
Nitric acid
Citric acid
Sulfuric acid
(b) Complete the sentence. A weak acid is only .................... ionised in aqueous solution.[1]
(c) A strong acid and a weak acid have the same concentration. Which acid has the lower pH?[1]
(d) Solution X has a pH of 3. Solution Y has a pH of 4. Which solution has the higher concentration of hydrogen ions?[1]
Show the answer and mark scheme
(a)Answer: Citric acid
(b)Answer: partially
partially / partly
(c)Answer: the strong acid
the strong acid
(d)Answer: X
X
Question 2Medium5 marks
Acids can be described as strong or weak.
(a) What is meant by a strong acid?[1]
(b) Give one example of a weak acid.[1]
(c) Which statement about a weak acid is correct? Tick (✓) one box.[1]
It is always a dilute solution.
It is only partially ionised in aqueous solution.
It has a pH greater than 7.
It contains no hydrogen ions.
(d) The ionisation of hydrochloric acid and ethanoic acid in water can be shown as: HCl(aq) → H+(aq) + Cl−(aq) CH3COOH(aq) ⇌ H+(aq) + CH3COO−(aq) Explain what the different arrows show about the two acids.[2]
Show the answer and mark scheme
(a)
an acid that is completely ionised in aqueous solution
(b)Answer: ethanoic acid (or citric acid or carbonic acid)
ethanoic acid / citric acid / carbonic acid
(c)Answer: It is only partially ionised in aqueous solution.
(d)
→ shows that hydrochloric acid ionises completely (strong acid)
⇌ shows that ethanoic acid only partially ionises / the ionisation is reversible (weak acid)
Question 3Hard5 marks
As the pH of a solution decreases by one unit, the hydrogen ion concentration increases by a factor of 10.
(a) Solution A has a pH of 2. Solution B has a pH of 4. How many times greater is the hydrogen ion concentration in solution A than in solution B?[1]
(b) The hydrogen ion concentration of a solution with a pH of 3 is decreased by a factor of 10. Give the new pH.[1]
(c) Lemon juice has a pH of 2. Rainwater has a pH of 5. How many times greater is the hydrogen ion concentration in lemon juice than in rainwater?[1]
(d) A student added 10 cm3 of hydrochloric acid with a pH of 1 to 990 cm3 of distilled water and mixed it. Predict the pH of the new solution. Explain your answer.[2]
Show the answer and mark scheme
(a)Answer: 100 times
100
(b)Answer: 4
4
(c)Answer: 1000 times
1000
(d)Answer: pH 3
the volume increases 100 times, so the hydrogen ion concentration becomes 100 times smaller