Question

When dilute hydrochloric acid is added to a sodium compound A, then brisk effervescence of a gas B is produced. On passing this gas through lime-water, the lime-water turns milky forming an insoluble compound C. When excess of gas is passed, the insoluble compound dissolves forming a soluble compound D.
(a) What could be compound A?
(b) Name the gas B.
(c) Name the insoluble compound C.
(d) Name the soluble compound D.

Answer 1

(a) Compound "A" must contain a carbonate as it gives brisk effervescence with hydrochloric acid. So, compound "A" must be sodium bicarbonate (${\mathrm{Na}}_2{\mathrm{CO}}_3$).

(b) When dilute hydrochloric acid is added to a sodium compound A, then brisk effervescence of gas is produced which means carbon dioxide gas is released during the reaction. Carbon dioxide on passing through lime water, turns lime water milky.

${\mathrm{Na}}_2{\mathrm{CO}}_3+2\mathrm{HCl}\to 2\mathrm{NaCl}+{\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}$

(c) When carbon dioxide is treated with lime water (calcium hydroxide), it forms insoluble compound "C" which is calcium carbonate.

$\mathrm{Ca}(\mathrm{OH}{)}_2+{\mathrm{CO}}_2\to {\mathrm{CaCO}}_3+{\mathrm{H}}_2\mathrm{O}$

(d) When an excess of carbon dioxide is passed through an aqueous solution of calcium carbonate, it forms compound "D" which is calcium bicarbonate.

${\mathrm{CaCO}}_3+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2\to \mathrm{Ca}({\mathrm{HCO}}_3{)}_2$