WA1 Practice Paper: Weighted Assessment 1 — question paper

Section A: Multiple-choice questions[10 marks]

Answer all questions. For each question, write the letter (A, B, C or D) of the correct answer.

1. 1

   Which change is oxidation?

   1. AFe³⁺ changing to Fe²⁺
   2. BCl₂ changing to Cl⁻
   3. CFe²⁺ changing to Fe³⁺
   4. DO₂ changing to O²⁻
   ( )
2. 2

   In the reaction Zn + CuSO₄ → ZnSO₄ + Cu, the oxidising agent is

   1. AZn
   2. BCuSO₄
   3. CZnSO₄
   4. DCu
   ( )
3. 3

   Which reaction is not a redox reaction?

   1. AZn + 2HCl → ZnCl₂ + H₂
   2. B2Mg + O₂ → 2MgO
   3. CHNO₃ + KOH → KNO₃ + H₂O
   4. DCuO + H₂ → Cu + H₂O
   ( )
4. 4

   The oxidation state of nitrogen in the nitrate ion, NO₃⁻, is

   1. A+3
   2. B+6
   3. C−3
   4. D+5
   ( )
5. 5

   A liquid conducts electricity during electrolysis. This shows the liquid

   1. Acontains free electrons
   2. Bcontains mobile ions
   3. Cis a covalent molecular liquid
   4. Dmust be a metal
   ( )
6. 6

   Molten lead(II) bromide is electrolysed using inert electrodes. The product at the cathode is

   1. Abromine
   2. Bhydrogen
   3. Clead
   4. Dlead bromide
   ( )
7. 7

   Concentrated aqueous sodium chloride is electrolysed using inert electrodes. The gas formed at the anode is

   1. Achlorine
   2. Boxygen
   3. Chydrogen
   4. Dsteam
   ( )
8. 8

   A metal spoon is to be electroplated with silver. The spoon must be connected as the

   1. Aanode
   2. Bcathode
   3. Celectrolyte
   4. Dinert electrode
   ( )
9. 9

   Which pair of electrodes is inert?

   1. Acopper and silver
   2. Biron and zinc
   3. Csodium and nickel
   4. Dplatinum and graphite
   ( )
10. 10

    During the electrolysis of dilute sulfuric acid, hydrogen forms at the cathode because

    1. AH⁺ ions gain electrons at the cathode
    2. BH⁺ ions lose electrons at the cathode
    3. Csulfate ions are attracted to the cathode
    4. Dwater molecules carry the current as wholes
    ( )

Section B: Structured questions[30 marks]

Answer all questions in the spaces provided. Show all necessary working. Give numerical answers to 3 significant figures where appropriate, with units.

1. 1

   Iron is extracted from iron(III) oxide in a blast furnace: Fe₂O₃ + 3CO → 2Fe + 3CO₂.

   1. (a)

      State the change in oxidation state of iron and of carbon in this reaction.

      [3]
   2. (b)

      Name the oxidising agent in this reaction.

      [1]
   3. (c)

      Write the ionic half-equation for the reduction that occurs.

      [2]
2. 2

   Chlorine water is added to aqueous potassium bromide. The solution turns orange-brown: Cl₂ + 2KBr → 2KCl + Br₂.

   1. (a)

      Explain, in terms of electrons, why the bromide ions are oxidised.

      [3]
   2. (b)

      State why chlorine is able to oxidise bromide ions but iodine is not.

      [2]
   3. (c)

      Predict, with a reason, what is seen when chlorine water is added to aqueous potassium iodide.

      [1]
3. 3

   A student electrolyses molten sodium chloride in one cell and dilute aqueous sodium chloride in a second cell, both with inert electrodes.

   1. (a)

      Name the product at each electrode for the molten salt.

      [2]
   2. (b)

      Write the half-equation for the reaction at each electrode of the molten cell.

      [2]
   3. (c)

      Name the product at the cathode when the dilute aqueous salt is electrolysed, and explain why sodium metal is not formed.

      [3]
   4. (d)

      State why the anode product differs between the two cells.

      [1]
4. 4

   A steel spoon is to be electroplated with silver.

   1. (a)

      State which electrode the spoon is made and which terminal it is connected to.

      [1]
   2. (b)

      Name a suitable electrolyte.

      [1]
   3. (c)

      Write the half-equation for the reaction at the spoon.

      [2]
   4. (d)

      The anode is a lump of silver. State and explain what happens to it as the plating proceeds.

      [2]
5. 5

   Copper is purified by electrolysis using an impure copper anode, a pure copper cathode and aqueous copper(II) sulfate.

   1. (a)

      Write the half-equation at the cathode.

      [2]
   2. (b)

      State what happens to the unreactive impurities, such as silver, in the impure anode.

      [1]
   3. (c)

      State one reason why the electrolyte stays at a constant concentration during refining.

      [1]