Question

A substance ‘X’ is used in white-washing and is obtained by heating limestone in the absence of air. Identify ‘X’.
(a) CaOCl2
(b) Ca (OH)2
(c) CaO
(d) CaCO3

Answer 1

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UR ANSWER IS (C)

The chemical substance X used for whitewashing is Calcium oxide also known as quicklime or burnt lime or lime. Calcium oxide is an alkaline earth flux with the chemical formula CaO.

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Answer 2

Substance 'X' is identified - (c) CaO.

Which substance is obtained by heating limestone?

On heating calcium carbonate, calcium oxide will be obtained as follows-

$CaCO_{3} \rightarrow CaO+CO_{2}$

Thus, carbon dioxide and calcium oxide are obtained by heating limestone.

This CaO obtained is also known by the name quick lime or burnt lime as it is obtained on burning calcium oxide.

Calcium oxide in whitewashing of walls:

• Upon reacting with water, calcium oxide produces calcium hydroxide.
• This calcium hydroxide then forms calcium carbonate as it reacts with carbon dioxide present in the atmosphere.
• This calcium carbonate results in a hard coating on the wall, which is whitewashing.