Question

A solution of a substance ‘X’ is used for whitewashing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with
water.
Why can't that substance X be Ca(OH)2 ?

Answer 1

Answer:

i)CaO= calcium oxide

ii)CaO+H2O=Ca(OH)2

Substance X can't be Ca(OH)2 because in question the substance is asked not the solution (mixture of a substance and a liquid). So the substance is CaO and it's solution with water is Ca(OH)2.

Hope it helps.

Answer 2

Answer:

(i) The substance 'X' which is used for whitewashing is calcium oxide also known as quicklime with chemical formula CaO .

(ii) When 'X' is reacted with water, it forms calcium hydroxide [ Ca(OH)2 ].  

CaO (s) + H2O (l) → Ca(OH)2 (aq).

Quicklime is used for whitewashing as it produces calcium hydroxide (CaOH) when it reacts with water (H2O) and absorbs carbon dioxide (CO2) from the atmosphere and as a result it produces calcium carbonate (CaCO3) which creates a hard coating on the walls.

Explanation: