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JAMB Chemistry 1987 Question 30

Question 30

Halogens

Which of the following equations correctly represents the action of hot concentrated alkaline solution on chlorine?

  1. A.Cl2(g) + 2OH−(aq) → OCl−(aq) + Cl−(aq) + H2O(l)
  2. B.3Cl2(g) + 6OH−(aq) → ClO3−(aq) + 5Cl−(aq) + 3H2O(l)
  3. C.3Cl2(g) + 6OH−(aq) → ClO3−(s) + 5Cl−(aq) + 3H2O(l)
  4. D.3Cl2(g) + 6OH−(aq) → 5ClO3−(aq) + Cl−(aq) + 3H2O(l)
Show the answer and explanation

Answer: B (3Cl2(g) + 6OH−(aq) → ClO3−(aq) + 5Cl−(aq) + 3H2O(l))

Explanation

Hot concentrated alkali turns chlorine into chlorate(V) and chloride in the ratio 1 : 5. The chlorate ion stays dissolved, so it is (aq), not (s). Option A is the reaction with cold dilute alkali.