Chapter 10 Practice Paper: Electrolysis — question paper

Section A: Multiple-choice questions[10 marks]

Choose one answer for each question. Each question is worth 1 mark.

1. 1

   Ions can only carry current through an electrolyte when they are

   1. Afree to move
   2. Bfrozen in place
   3. Cneutral atoms
   4. Dshared as pairs
   ( )
2. 2

   Positive ions (cations) migrate to

   1. Athe anode, the positive electrode
   2. Bthe electrolyte surface
   3. Cthe power switch
   4. Dthe cathode, the negative electrode
   ( )
3. 3

   Molten sodium chloride gives what at the cathode?

   1. AHydrogen gas
   2. BSodium hydroxide
   3. CSodium metal
   4. DChlorine gas
   ( )
4. 4

   Electrolysing aqueous potassium sulfate with inert electrodes gives

   1. Apotassium oxide everywhere
   2. Bhydrogen at the cathode and oxygen at the anode
   3. Cpotassium at the cathode
   4. Dsulfur at the anode
   ( )
5. 5

   Concentrated brine turns alkaline during electrolysis because

   1. ANaOH is added at the anode
   2. Bchlorine dissolves to make alkali
   3. Cthe cathode dissolves
   4. DH⁺ and Cl⁻ are removed as gases, leaving OH⁻ behind
   ( )
6. 6

   Cryolite’s job in the aluminium cell is to

   1. Aslow the reaction down
   2. Bdissolve alumina so the cell runs much cooler than 2072 °C
   3. Creact with the anodes
   4. Dcolour the aluminium
   ( )
7. 7

   The half equation 2Cl⁻ → Cl₂ + 2e⁻ represents

   1. Aoxidation at the anode
   2. Breduction at the cathode
   3. Creduction at the anode
   4. Doxidation at the cathode
   ( )
8. 8

   Cu²⁺ + 2e⁻ → Cu is balanced for

   1. Acharge only
   2. Bneither
   3. Catoms and charge
   4. Datoms only
   ( )
9. 9

   Electrolysing dilute sulfuric acid produces gas volumes of

   1. Atwice as much oxygen as hydrogen
   2. Bequal volumes
   3. Coxygen only
   4. Dtwice as much hydrogen as oxygen
   ( )
10. 10

    The blue colour of copper sulfate solution fades during electrolysis with inert electrodes because

    1. Acopper sulfate is destroyed at both electrodes
    2. BCu²⁺ ions are reduced to copper metal at the cathode
    3. CSO₄²⁻ oxidises the water
    4. Dthe anode absorbs blue light
    ( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided.

1. 11

   A student electrolyses molten lithium chloride with inert electrodes.

   1. (a)

      State the product at each electrode.

      [2]
   2. (b)

      Give the half equation for the lithium ions gaining electrons.

      [2]
   3. (c)

      Give the half equation showing chloride ions forming chlorine molecules.

      [2]
2. 12

   Three solutions are electrolysed with inert electrodes: concentrated sodium chloride, dilute sulfuric acid, and silver nitrate.

   Solutions

   Solution	Cathode	Anode
   Concentrated NaCl	?	?
   Dilute H₂SO₄	?	?
   AgNO₃	?	?

   1. (a)

      Complete the table with the product at each electrode.

      [6]
   2. (b)

      State one safety precaution for the chlorine in this experiment.

      [1]
   3. (c)

      Explain why silver forms but sodium does not.

      [1]
3. 13

   The aluminium extraction cell runs 24 hours a day near cheap power stations.

   1. (a)

      Explain why aluminium oxide must be dissolved in molten cryolite rather than melted on its own.

      [2]
   2. (b)

      Write the half equations at the cathode and the anode.

      [3]
   3. (c)

      Explain why the anodes must be replaced regularly.

      [1]