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JAMB Chemistry 1978 Question 36

Question 36

Hydrocarbons

Two gas cylinders contain ethylene (ethene) and acetylene respectively. One test which can be used to distinguish between them is by

  1. A.passing each gas through bromine water
  2. B.passing each gas through dilute potassium permanganate solution
  3. C.passing each gas through silver nitrate solution
  4. D.passing each gas through ammoniacal copper (I) chloride solution
  5. E.treating each gas catalytically with excess hydrogen gas.
Show the answer and explanation

Answer: D (passing each gas through ammoniacal copper (I) chloride solution)

Explanation

Ethyne (acetylene) has an acidic terminal hydrogen and gives a red-brown precipitate with ammoniacal copper(I) chloride; ethene does not. Both decolourise bromine water and permanganate.