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JAMB Chemistry 1979 Question 29

Question 29

Redox Reactions

In which of the following reactions is sulphur dioxide acting as an oxidizing agent?

  1. A.SO2 + 2HNO3 → H2SO4 + NO2 + Heat
  2. B.2SO2 + 2H2O + O2 → 2H2SO4.
  3. C.SO2 + 2H2O + Cl2 → H2SO4 + 2HCl.
  4. D.SO2 + 2H2S → 3S + 2H2O.
  5. E.SO2 + H2O → H2SO3.
Show the answer and explanation

Answer: D (SO2 + 2H2S → 3S + 2H2O.)

Explanation

In D the sulphur in SO2 goes from +4 to 0 (it is reduced), oxidising H2S to sulphur. In A, B and C SO2 is itself oxidised to H2SO4.