Practise 23 exam-style questions on Metal hydroxides (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.
23 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
Sodium hydroxide solution is added to iron(II) sulfate solution.
Name the precipitate that forms and give its colour.
Model answer
Iron(II) hydroxide, which is a green precipitate.
Explanation
The metal ion swaps partners with the hydroxide ion: Fe²⁺ + 2OH⁻ → Fe(OH)₂. Iron(II) hydroxide is insoluble and green.
Mark scheme
1 mark
iron(II) hydroxide
allow Fe(OH)₂; do not accept iron hydroxide without (II) or iron(III) hydroxide
1 mark
green
allow dark green / grey-green
Question 2
2 marks
Zinc ions form a white precipitate with sodium hydroxide solution. The precipitate dissolves when excess sodium hydroxide solution is added.
Explain why sodium hydroxide solution cannot be used to distinguish between a solution of zinc ions and a solution of aluminium ions.
Model answer
Zinc ions and aluminium ions both form a white precipitate with sodium hydroxide, and both precipitates dissolve in excess sodium hydroxide. The observations are identical, so the test cannot tell them apart.
Explanation
A test can only distinguish two ions if they give different results. Here a different method would be needed, such as an instrumental method like flame emission spectroscopy.
Mark scheme
1 mark
both form a white precipitate
1 mark
both precipitates dissolve in excess (so the results are identical)
Question 3
3 marks
A student adds sodium hydroxide solution to iron(II) chloride solution. A green precipitate forms. After the test tube is left open to the air for an hour, the surface of the precipitate has turned orange-brown.
Suggest an explanation for this change.
Model answer
At the surface, the green iron(II) hydroxide reacts with oxygen from the air. The iron(II) is oxidised to iron(III) (each Fe²⁺ ion loses an electron), forming iron(III) hydroxide, which is orange-brown.
Explanation
Iron(II) compounds are easily oxidised to iron(III) compounds by air. This is why tests for iron(II) should be observed straight away: a green precipitate that slowly browns still shows iron(II) was present.
Mark scheme
1 mark
the iron(II) hydroxide reacts with oxygen in the air
1 mark
it is oxidised / iron(II) is converted to iron(III)
allow Fe²⁺ loses an electron to form Fe³⁺
1 mark
forming iron(III) hydroxide, which is brown
Question 4
4 marks
A technician has three unlabelled solutions: aluminium chloride, magnesium chloride and copper(II) chloride.
Describe how the technician could identify each solution using only sodium hydroxide solution. Give the results.
Model answer
Put a small sample of each solution into separate test tubes and add sodium hydroxide solution a few drops at a time. The solution that gives a blue precipitate is copper(II) chloride. The other two give white precipitates. Add excess sodium hydroxide to these two: the precipitate that dissolves is from aluminium chloride, and the one that remains is from magnesium chloride.
Explanation
Precipitate colour picks out the copper compound immediately. The two white precipitates are then distinguished by adding excess sodium hydroxide, because only aluminium hydroxide dissolves.
Mark scheme
1 mark
add sodium hydroxide solution a few drops at a time to a sample of each solution
1 mark
blue precipitate shows copper(II) chloride
1 mark
white precipitate with aluminium chloride and magnesium chloride
1 mark
add excess: the precipitate dissolves for aluminium chloride but remains for magnesium chloride
both outcomes needed
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