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JAMB Chemistry 1978 Question 18

Question 18

Electrolysis

During the electrolysis of copper II sulphate between platinum electrodes, if litmus solution is added to the anode compartment,

  1. A.the litmus turns blue but no gas is evolved.
  2. B.the litmus turns blue and oxygen is evolved
  3. C.the litmus turns blue and hydrogen is evolved
  4. D.the litmus turns red and oxygen is evolved
  5. E.the litmus turns red and then becomes colourless
Show the answer and explanation

Answer: D (the litmus turns red and oxygen is evolved)

Explanation

At an inert anode, hydroxide ions are discharged as oxygen, leaving excess H+ ions, so the solution there becomes acidic and turns litmus red.