JAMB - Chemistry (2018 - No. 85)
A sample of hard water contains some calcium sulphate and calcium hydrogen carbonate. The total hardness may therefore be removed by
boiling the water
adding excess calcium hydroxide
adding a calculated amount of calcium hydroxide
adding sodium carbonate
Erläuterung
its D because when sodium carbonate reacts with calcium hydrogentrioxocarbonate it gives sodium hydrogentrioxocarbonate and calcium trioxocarbonate. However, when it react with calcium sulphate, calcium carbonate and sodium tetraoxosulphate is formed