Chapter 2 Practice Paper: Electrolysis — question paper (print)

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Secondary 4 · Chemistry (G2 / G3)

Chapter 2 Practice Paper

Electrolysis

Duration: 40 minutes

Total: 30 marks

Name:

Class:

Date:

READ THESE INSTRUCTIONS FIRST

Write your name, class and register number in the spaces at the top of this page.
Answer all questions.
Give numerical answers correct to 3 significant figures unless stated otherwise, with units where a quantity is calculated.
Chemical equations should be balanced, with state symbols shown where the question asks for them.
The number of marks is given in brackets [ ] at the end of each question or part question.
The total number of marks for this paper is shown on its cover.

Original practice material written for the MOE Chemistry syllabus. It is not an official MOE or school examination paper. Chapter 2 (molten and aqueous electrolysis, selective discharge, plating, refining, simple cells).

For Examiner’s Use
Section A	/ 10
Section B	/ 20
Total	/ 30

Section A: Multiple-choice questions[10 marks]

Choose the one correct answer for each question.

1
Which substance conducts electricity by mobile electrons rather than by mobile ions?
1. Amolten lead(II) bromide
2. Bcopper wire
3. Caqueous sodium sulfate
4. Ddilute hydrochloric acid
( )
2
Molten sodium iodide is electrolysed using carbon electrodes. The observation at the anode is
1. Asilvery molten beads forming
2. Ba pale green gas bubbling off
3. Cpurple-grey vapour of a halogen
4. Da colourless gas that relights a glowing splint
( )
3
During the electrolysis of copper(II) sulfate solution with carbon electrodes, the mass of the cathode
1. Adecreases as copper dissolves
2. Bincreases as copper deposits
3. Cstays the same because the electrode is inert
4. Dincreases as oxygen bubbles off
( )
4
Dilute sodium chloride solution is electrolysed with inert electrodes. The anode product is
1. Achlorine
2. Bhydrogen
3. Coxygen
4. Dsodium hydroxide
( )
5
In a simple cell of zinc and copper strips in dilute sulfuric acid, electrons flow through the wires
1. Afrom zinc to copper, zinc being more reactive
2. Bfrom copper to zinc, copper being positive
3. Cfrom zinc to copper, zinc being positive
4. Din both directions alternately
( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided. Include state symbols where the question asks, and balance every equation.

1
Concentrated aqueous sodium chloride is electrolysed in an industrial cell with inert electrodes.
1. (a)
  Name the three products of this electrolysis and state where each forms.
  [3]
2. (b)
  Write the half-equation for the reaction at the cathode.
  [1]
3. (c)
  Explain why sodium metal is NOT produced at the cathode.
  [2]
2
A jewellery workshop gold-plates a brass pendant using a gold anode, the pendant as the other electrode, and a gold(I) cyanide bath (contains Au⁺ ions).
1. (a)
  State the polarity of the pendant and of the gold anode.
  [2]
2. (b)
  Write the half-equation at the pendant.
  [1]
3. (c)
  Explain why the mass of the gold anode decreases while the ion concentration of the bath stays constant.
  [2]
3
Predict the products at the cathode and anode for each electrolyte (inert electrodes): molten calcium bromide; aqueous copper(II) chloride (concentrated).
1. (a)
  Molten calcium bromide: cathode and anode products.
  [2]
2. (b)
  Concentrated aqueous copper(II) chloride: cathode and anode products.
  [2]
4
A student builds a simple cell with magnesium and lead strips in dilute hydrochloric acid.
1. (a)
  State which strip is the negative terminal and write the half-equation occurring there.
  [2]
2. (b)
  State the observation on the lead strip and write the half-equation.
  [2]
3. (c)
  State and explain the effect of replacing magnesium with zinc.
  [1]

— End of paper —