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JAMB Chemistry 1991 Question 18

Question 18

Water

A sample of temporary hard water can be prepared in the laboratory by

  1. A.dissolving calcium chloride in distilled water
  2. B.saturating lime water with carbon (IV) oxide
  3. C.saturating distilled water with calcium hydroxide
  4. D.dissolving sodium hydrogen trioxocarbonate (IV) in some distilled water.
Show the answer and explanation

Answer: B (saturating lime water with carbon (IV) oxide)

Explanation

Excess CO2 in lime water forms calcium hydrogen trioxocarbonate(IV), Ca(HCO3)2, which causes temporary hardness. Calcium chloride gives permanent hardness.