In electrolytic refining of copper, the electrolyte is a solution of
- A.acidified copper chloride.
- B.acidified copper sulphate.
- C.potassium chloride.
- D.sodium sulphate.
Correct answer
Explanation
The correct answer is B, acidified copper sulphate. In the electrolytic refining of copper, a solution of copper sulphate made acidic with a little dilute sulphuric acid carries the copper ions between the electrodes.
The impure copper is made the anode and a thin strip of pure copper is made the cathode. When current passes, copper from the anode dissolves into the solution as Cu²⁺ ions, and an equal amount of pure copper is deposited on the cathode. Less reactive impurities such as gold and silver do not dissolve and fall below the anode as anode mud, while more reactive impurities stay in the solution. The acid improves the conductivity of the solution and stops the copper salt from hydrolysing. This gives copper of about 99.9 per cent purity for electrical wiring.
A is wrong: copper chloride is not the standard electrolyte for this process.
C is wrong: potassium chloride contains no copper ions to deposit on the cathode.
D is wrong: sodium sulphate also has no copper ions and would not refine copper.
Exam tip: impure metal is the anode, pure metal is the cathode, and the electrolyte is a salt of the same metal.
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