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JAMB Chemistry 2005 Question 2

Question 2

Electrolysis

Which of the following ions requires the largest quantity of electricity for discharge at an electrode?

  1. A.4.0 moles of Cl−
  2. B.3.0 moles of Na+
  3. C.2.5 moles of Cu2+
  4. D.2.0 moles of Al3+
Show the answer and explanation

Answer: D (2.0 moles of Al3+)

Explanation

Faradays needed = moles × charge: Cl− 4 × 1 = 4F, Na+ 3 × 1 = 3F, Cu2+ 2.5 × 2 = 5F, Al3+ 2 × 3 = 6F. Al3+ needs the most.