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IGCSE · Practice questions · Electroplating and refining copper

Plate it, then purify it.

Six original Cambridge-style questions on electroplating and the refining of copper, including half-equations and changes in mass.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Object at the cathode.

01
Recall
[3 marks]

A student wants to nickel-plate a steel paperclip. State what should be used as (a) the cathode, (b) the anode and (c) the electrolyte.

  • (a) the steel paperclip. ✓
  • (b) a piece of nickel. ✓
  • (c) a solution containing nickel ions, for example nickel sulfate solution. ✓
02
Recall
[2 marks]

Give two reasons why metal objects are electroplated.

  • To improve their appearance. ✓
  • To protect them from corrosion. ✓
03
Explain
[2 marks]

Explain why the object to be plated must be connected to the negative terminal of the power supply.

  • The metal ions in the electrolyte are positive. ✓
  • They are attracted to the negative electrode (cathode), where they gain electrons and form a layer of metal on the object. ✓
04
Analysis
[4 marks]

(Extended) Compare the electrolysis of aqueous copper(II) sulfate using carbon electrodes with the electrolysis using copper electrodes. State what happens at each anode and to the colour of the solution in each case.

  • Carbon electrodes: oxygen is given off at the anode. ✓
  • Carbon electrodes: the blue colour fades as copper ions are removed. ✓
  • Copper electrodes: the copper anode dissolves, forming Cu2+ ions. ✓
  • Copper electrodes: the blue colour stays the same, because copper ions are replaced as fast as they are removed. ✓
05
Explain
[4 marks]

(Extended) Describe how impure copper is purified by electrolysis. Include the electrodes, the electrolyte and what happens to the impurities.

  • The anode is impure copper; the cathode is a thin sheet of pure copper. ✓
  • The electrolyte is copper(II) sulfate solution. ✓
  • Copper dissolves from the anode as Cu2+ ions and is deposited as pure copper on the cathode. ✓
  • The impurities fall to the bottom of the cell as anode sludge. ✓
06
Analysis
[2 marks]

(Extended) During refining, an impure copper anode loses 120 g and the cathode gains 114 g. Explain the difference and calculate the percentage purity of the copper that dissolved from the anode.

  • Only the copper is deposited on the cathode; 6 g of impurities fell to the bottom as sludge. ✓
  • Percentage purity = 114 ÷ 120 × 100 = 95%. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.