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JAMB Chemistry 1978 Question 39

Question 39

Separation of Mixtures

Which one of the following changes is physical?

  1. A.Adding iron filing to aerated water
  2. B.Adding sodium metal to water
  3. C.Cooling a solution of iron (II) sulphate to obtain the hydrated salt
  4. D.Cooling water to obtain ice
  5. E.Burning the domestic gas (Utilgas) for cooking.
Show the answer and explanation

Answer: D (Cooling water to obtain ice)

Explanation

Freezing water only changes its state; no new substance forms and it is easily reversed. The others form new substances (rust, NaOH, combustion products, a hydrated salt with water of crystallisation).