Reactions of ions in aqueous solutionAQA A-Level Chemistry: Topic test

20 questions, 54 marks

AQA A-Level Chemistry

Reactions of ions in aqueous solution topic test

Total 54 marks

Name

Class

Date

1
Gardeners add aluminium sulfate to soil to turn hydrangea flowers blue. A 0.10 mol dm⁻³ aqueous solution of aluminium sulfate has a pH of about 3, so the soil becomes more acidic as well.
(a)
What is the formula of the ion present in aqueous aluminium sulfate?
[1 mark]
A[Al(H₂O)₆]³⁺
B[Al(H₂O)₄]³⁺
C[Al(OH)₆]³⁻
D[Al(H₂O)₆]²⁺
(b)
Which statement explains why the solution is acidic?
[1 mark]
ASulfate ions react with water to release H⁺ ions
BAl³⁺ ions react with water to release OH⁻ ions
CThe Al³⁺ ion polarises the water ligands, weakening their O–H bonds so that H⁺ is released
DAluminium has an incomplete d sub-level which accepts protons
(c)
Write an equation to show why the solution is acidic and explain, in terms of charge and size, why the Al³⁺ ion has this effect.
[2 marks]
Total for question 1: 4 marks
2
Bordeaux mixture, a copper-based fungicide, is made by adding calcium hydroxide solution to aqueous copper(II) sulfate. A blue precipitate forms.
(a)
What is the formula of the blue precipitate?
[1 mark]
ACuO
BCu(OH)₂
CCuCO₃
DCu(OH)₃
(b)
Which equation represents the formation of the precipitate?
[1 mark]
A[Cu(H₂O)₆]²⁺ + 2OH⁻ → [Cu(H₂O)₄(OH)₂]²⁻ + 2H₂O
B[Cu(H₂O)₆]²⁺ + 2OH⁻ → [Cu(H₂O)₆(OH)₂]
C[Cu(H₂O)₆]²⁺ + 2OH⁻ → [Cu(H₂O)₄(OH)₂] + H₂O
D[Cu(H₂O)₆]²⁺ + 2OH⁻ → [Cu(H₂O)₄(OH)₂] + 2H₂O
(c)
The blue precipitate does not dissolve when excess sodium hydroxide is added, whereas aluminium hydroxide does. Explain why aluminium hydroxide dissolves in excess hydroxide ions.
[2 marks]
Total for question 2: 4 marks
3
Aqueous sodium hydroxide is added dropwise to iron(II) sulfate solution until it is in excess. A green precipitate forms, and the surface of the precipitate slowly turns brown on standing in air.
(a)
Identify the green precipitate and the brown solid, and state what happens to the green precipitate when more sodium hydroxide is added.
[3 marks]
(b)
Explain, with an equation, how the precipitate forms when hydroxide ions are added to [Fe(H₂O)₆]²⁺, and why it is a precipitate rather than a solution.
[4 marks]
Total for question 3: 7 marks
4
In the Bayer process, crushed bauxite, which is mainly aluminium oxide with iron(III) oxide as the main impurity, is heated with concentrated aqueous sodium hydroxide. The aluminium compounds dissolve but the iron(III) oxide does not, and is filtered off as red-brown 'red mud'. Aluminium hydroxide is then precipitated from the filtrate. A sample of the red mud can be dissolved in the minimum volume of dilute sulfuric acid to give a solution containing [Fe(H₂O)₆]³⁺.
(a)
Explain, with equations, why the aluminium compounds dissolve in sodium hydroxide whereas the iron(III) compounds do not, and how aluminium hydroxide is then precipitated from the filtrate by adding dilute acid dropwise.
[6 marks]
(b)
Aqueous sodium carbonate is added to the solution of [Fe(H₂O)₆]³⁺ from the red mud. Describe and explain what is seen, with equations, and state how the result would differ for a solution of iron(II) ions.
[6 marks]
Total for question 4: 12 marks
5
Separate samples of aluminium sulfate solution and iron(III) chloride solution are each treated with aqueous ammonia and with aqueous sodium hydroxide, in each case added dropwise and then in excess.
(a)
What is observed when excess aqueous ammonia is added to the aluminium sulfate solution?
[1 mark]
AA white precipitate that dissolves to give a colourless solution
BA blue precipitate that dissolves to give a deep blue solution
CA brown precipitate that does not dissolve
DA white precipitate that does not dissolve
(b)
Which reagent, added in excess to separate samples of the two solutions, gives a precipitate that dissolves with only one of them?
[1 mark]
AAqueous sodium hydroxide
BAqueous ammonia
CAqueous sodium carbonate
DDilute hydrochloric acid
(c)
Explain why aluminium hydroxide precipitated by ammonia does not dissolve in excess ammonia, although it dissolves in excess sodium hydroxide.
[2 marks]
Total for question 5: 4 marks
6
Copper(II) carbonate is prepared in the laboratory by adding aqueous sodium carbonate to aqueous copper(II) sulfate.
(a)
What is observed when the sodium carbonate is added?
[1 mark]
AA blue-green precipitate with bubbles of carbon dioxide
BA white precipitate with no effervescence
CA blue-green precipitate with no effervescence
DA deep blue solution forms and no precipitate appears
(b)
Why does no gas form in this reaction?
[1 mark]
ACopper(II) carbonate is soluble, so the carbonate ions remain in solution
B[Cu(H₂O)₆]²⁺ is not acidic enough to donate protons to carbonate ions and release CO₂
CCarbonate ions are oxidised by copper(II) ions
DCopper(II) hydroxide is amphoteric and absorbs the gas
(c)
State what would be observed if sodium carbonate were added to aluminium sulfate solution instead, and explain the difference from copper(II) sulfate.
[2 marks]
Total for question 6: 4 marks
7
A student adds aqueous ammonia dropwise, then in excess, to a solution containing both copper(II) ions and iron(III) ions. A brown precipitate remains suspended in a deep blue solution. The mixture is filtered and the brown solid is washed with water.
(a)
Identify the brown solid and the species that makes the solution deep blue, and explain why the copper does not remain in the precipitate.
[3 marks]
(b)
The brown solid is dissolved in dilute sulfuric acid. Write an equation for the reaction, and explain what this shows about the nature of iron(III) hydroxide and how it differs from aluminium hydroxide.
[4 marks]
Total for question 7: 7 marks
8
Aluminium sulfate is added to water at a treatment works and the pH is adjusted with sodium hydroxide solution. A gelatinous white precipitate of aluminium hydroxide forms and traps suspended particles, which then settle out. The precipitate redissolves if the water is made too alkaline. Iron(III) sulfate is an alternative that works over a wider pH range, but a manager proposes using the cheaper iron(II) sulfate instead.
(a)
Explain, with equations, how the aluminium hydroxide precipitate forms when sodium hydroxide is added to the aluminium sulfate solution, and why too much alkali stops the treatment working.
[6 marks]
(b)
Explain, by comparing the acidity of the aqua ions and the behaviour of their hydroxides, why the iron(III) sulfate works over a wider pH range than aluminium sulfate, and why the manager's proposed iron(II) sulfate would be less effective.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).