passwella.
Menu

JAMB Chemistry 1978 Question 17

Question 17

Water

A sample of hard water contains some calcium sulphate and calcium hydrogen carbonate. The total hardness may therefore be removed by:

  1. A.boiling the water
  2. B.adding excess calcium hydroxide
  3. C.adding a calculated amount of calcium hydroxide
  4. D.adding sodium carbonate
  5. E.adding magnesium hydroxide.
Show the answer and explanation

Answer: D (adding sodium carbonate)

Explanation

Sodium carbonate precipitates the calcium ions from both the sulphate (permanent hardness) and the hydrogen carbonate (temporary hardness) as calcium carbonate. Boiling and calcium hydroxide only remove temporary hardness.