Question

When water is added to a white solid X, a hissing sound is heard and a lot of heat is produced forming a product Y. A suspension of Y in water is applied to the walls of the house during whitewashing. A clear solution of Y is also used for testing

{CO}_{2}

gas in the laboratory.
(a) Identify the solid X and write its chemical formula.
(b) Identify product Y and write its chemical formula.
(c) What is the common name of the solution of Y which is used for testing carbon dioxide gas?
(d) Write the chemical equation of the reaction which takes place on adding water to solid X.

Accepted Answer

(a) X is calcium oxide having formula $CaO$ . Calcium oxide reacts with water vigorously; it is an exothermic reaction.

(b) Y is Calcium hydroxide, its formula is $Ca (OH)_{2}$ . A suspension of Y in water is applied to the walls of the house during whitewashing. A solution of calcium hydroxide in water is lime water, which is used for testing the presence of carbon dioxide gas.

(c) The common name of the solution of Y, which is used for testing carbon dioxide gas is lime water.

(d) Reaction between calcium oxide and water is:

$\underset{(Calcium oxide)}{CaO (s)} + H_{2} O (l) \to \underset{(Calcium hydroxide)}{Ca (OH)_{2} (aq)} + Heat$

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