1. 1
   A student in a school laboratory is preparing a sample of pure, dry copper(II) chloride crystals by reacting dilute hydrochloric acid with excess copper(II) oxide powder, an insoluble base, following the standard method for preparing a soluble salt from an insoluble reactant.

   (a)

   A student in a school laboratory reacts dilute hydrochloric acid with excess copper(II) oxide powder to prepare a sample of copper(II) chloride. Copper(II) oxide acts as a base in this reaction. In terms of proton transfer, what role does the base play?

   [1 mark]

   • AProton donor
   • BProton acceptor
   • CElectron donor only
   • DNeither donor nor acceptor

   (b)

   After the reaction is complete, the student needs to separate the unreacted excess copper(II) oxide from the copper(II) chloride solution. Which technique should be used?

   [1 mark]

   • AFiltration
   • BSimple distillation
   • CChromatography
   • DFractional distillation

   (c)

   Describe the remaining steps the student should follow, after filtering off the excess copper(II) oxide, to obtain pure, dry crystals of copper(II) chloride from the filtrate.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A jeweller is preparing a small sample of insoluble silver chloride to use as a test reagent, by mixing a solution of silver nitrate with a solution of sodium chloride, a method used to make an insoluble salt by precipitation from two soluble reactants.

   (a)

   A jeweller wants to prepare a sample of insoluble silver chloride to use as a test reagent, by mixing two soluble salt solutions: silver nitrate and sodium chloride. Which general rule of solubility explains why silver chloride forms as a solid in this reaction?

   [1 mark]

   • AAll nitrates are insoluble
   • BAll sodium compounds are insoluble
   • CAll chlorides are soluble, except those of silver and lead
   • DAll chlorides are insoluble

   (b)

   After mixing the two solutions and the silver chloride precipitate forms, what technique should the jeweller use to obtain the pure, dry insoluble salt?

   [1 mark]

   • AUse paper chromatography
   • BEvaporate the whole mixture to dryness directly
   • CDistil the mixture
   • DFilter, then wash the residue with distilled water, then dry

   (c)

   Explain why washing the silver chloride precipitate with distilled water is an important step, and state what by-product remains in solution after the precipitate has been filtered off.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A farmer wants to prepare magnesium sulfate to use as a fertiliser additive, and plans to react dilute sulfuric acid with excess magnesium carbonate, an insoluble reactant, to produce a soluble salt solution that can later be crystallised.

   (a)

   A farmer wants to make magnesium sulfate fertiliser by reacting dilute sulfuric acid with magnesium carbonate. Describe the reactions of dilute sulfuric acid with a metal, with a base, and with a metal carbonate, naming the products formed in each case (you do not need to write equations).

   [3 marks]

   (b)

   Describe, step by step, how the farmer could prepare a pure, dry sample of magnesium sulfate crystals starting from dilute sulfuric acid and excess magnesium carbonate.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school technician is preparing a large batch of pure, dry hydrated copper(II) sulfate crystals from copper(II) oxide and dilute sulfuric acid, to be used as a demonstration sample in future chemistry lessons on salt preparation and crystallisation.

   (a)

   A school technician needs to prepare a large batch of pure, dry hydrated copper(II) sulfate crystals for use in future lessons, starting from copper(II) oxide and dilute sulfuric acid. Describe, in full detail, the complete practical method the technician should follow, from reacting the two substances to obtaining dry, hydrated crystals.

   [6 marks]

   (b)

   During the crystallisation stage, the technician notices that heating the saturated copper(II) sulfate solution too strongly, or for too long, produces a pale, almost white powder instead of blue crystals. Explain what has happened to the copper(II) sulfate in this case, and evaluate why controlling the heating carefully is essential to obtaining the correct hydrated product.

   [6 marks]

   Total for question 4: 12 marks

End of questions