A sample of hard water contains some calcium sulphate and calcium hydrogen carbonate. The total hardness may therefore be removed by
A. boiling the water B. adding excess calcium hydroxide C. adding a calculated amount of calcium hydroxide D. adding sodium carbonate
Correct Answer: D
Explanation
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
