Reactions of metal ions with hydroxide, ammonia and carbonateAQA A-Level Chemistry: Subtopic test

1. 1
   A technician has four unlabelled bottles of aqueous solution. They contain copper(II) sulfate, iron(II) sulfate, iron(III) chloride and aluminium nitrate. She adds sodium hydroxide solution dropwise to a sample of each, and then in excess, and records the observations.

   (a)

   Which solution gives a white precipitate that dissolves in excess sodium hydroxide solution?

   [1 mark]

   • AAluminium nitrate
   • BCopper(II) sulfate
   • CIron(II) sulfate
   • DIron(III) chloride

   (b)

   Which observation is characteristic of the iron(II) sulfate solution?

   [1 mark]

   • AA pale blue precipitate that is insoluble in excess sodium hydroxide
   • BA brown precipitate that is formed immediately
   • CA green precipitate that turns brown at the surface on standing in air
   • DA white precipitate that darkens on standing

   (c)

   Write equations to show that aluminium hydroxide is amphoteric.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student adds aqueous ammonia dropwise to copper(II) sulfate solution. A pale blue precipitate forms. When more ammonia is added the precipitate dissolves, giving a deep blue solution.

   (a)

   What is the formula of the ion responsible for the deep blue solution?

   [1 mark]

   • A[Cu(NH₃)₆]²⁺
   • B[Cu(NH₃)₂(H₂O)₄]²⁺
   • C[Cu(NH₃)₄(H₂O)₂]⁺
   • D[Cu(NH₃)₄(H₂O)₂]²⁺

   (b)

   What type of reaction occurs when the precipitate dissolves in excess ammonia?

   [1 mark]

   • AAcid–base
   • BLigand substitution
   • CRedox
   • DPrecipitation

   (c)

   Write an equation for the formation of the pale blue precipitate and state the role of ammonia in this reaction.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student adds sodium carbonate solution to separate samples of iron(II) sulfate solution and iron(III) sulfate solution of the same concentration.

   (a)

   Describe the observations made with each solution.

   [3 marks]

   (b)

   Explain, with equations, why the two solutions behave differently.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Four aqueous solutions, W, X, Y and Z, each contain one of the ions Al³⁺, Cu²⁺, Fe²⁺ and Fe³⁺. Adding sodium hydroxide: W gives a pale blue precipitate that is insoluble in excess; X gives a white precipitate that dissolves in excess to give a colourless solution; Y gives a green precipitate that slowly darkens at the surface in air and is insoluble in excess; Z gives a brown precipitate that is insoluble in excess. Adding aqueous ammonia: W gives a pale blue precipitate that dissolves in excess to give a deep blue solution; X gives a white precipitate insoluble in excess; Y gives a green precipitate; Z gives a brown precipitate.

   (a)

   Identify W, X, Y and Z. Explain how the results support each identification, naming the precipitates and any complex ion formed.

   [6 marks]

   (b)

   Sodium carbonate solution is added to separate samples of W, X, Y and Z. X and Z each give a precipitate and effervescence. W and Y each give a precipitate only. Explain these observations, including equations for one M²⁺ ion and one M³⁺ ion.

   [6 marks]

   Total for question 4: 12 marks

End of questions