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JAMB Chemistry 1979 Question 10

Question 10

Electrolysis

Which of the following statements applies during the electrolysis of sodium hydroxide solution using platinum electrodes?

  1. A.Na+ ions are discharged at the cathode
  2. B.Hydrogen ions are discharged at the anode
  3. C.The concentration of sodium hydroxide decreases at both electrode compartments
  4. D.The concentration of sodium hydroxide increases at the cathode only.
  5. E.The concentration of sodium hydroxide increases at the anode only.
Show the answer and explanation

Answer: D (The concentration of sodium hydroxide increases at the cathode only.)

Explanation

At the cathode, hydrogen is released from water, leaving extra OH− with the Na+, so NaOH becomes more concentrated there. At the anode OH− ions are discharged as oxygen, so it gets weaker there.