Question

Which gas is released on the addition of dilute acid to calcium carbonate?
(A) ${{\text{N}}_{\text{2}}}$
(B) \[{\text{CaO}}\]
(C) ${\text{C}}{{\text{l}}_{\text{2}}}$
(D) ${\text{N}}{{\text{O}}_{\text{2}}}$
(E) ${\text{C}}{{\text{O}}_{\text{2}}}$

Answer 1

Hint: Acids on reaction with metals, bases and carbonates produce salts.
The gas liberated during the reaction of a carbonate with an acid can be detected by passing the gas through lime water.

Complete step by step answer:
When an acid reacts with a metal carbonate, a salt, water and carbon dioxide gas are produced. The general reaction can be written as follows.
${\text{acid + metalcarbonate}} \to {\text{salt + water + carbondioxide}}$
For example, sulphuric acid reacts with iron (II) carbonate to yield iron (II) sulphate, water and carbon dioxide gas.
${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{ + FeC}}{{\text{O}}_{\text{3}}} \to {\text{FeS}}{{\text{O}}_{\text{4}}} + {{\text{H}}_{\text{2}}}{\text{O}} + {\text{C}}{{\text{O}}_2}$
Similarly, calcium carbonate is a metal carbonate and so it will react with a dilute acid like hydrochloric acid to yield a salt calcium chloride, water and carbon dioxide gas.
\[{\text{CaC}}{{\text{O}}_{\text{3}}}{\text{ + 2HCl}} \to {\text{CaC}}{{\text{l}}_2} + {\text{C}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}}\]
The carbon dioxide gas causes bubbling during the reaction. It can be detected by passing it through lime water or calcium hydroxide, which will turn milky because of the formation of calcium carbonate which is insoluble in water.

Thus, the correct option is E.

Additional information:
All metal carbonates undergo one common reaction which is thermal decomposition. When a metal carbonate is heated, it undergoes breakdown to form the corresponding metal oxide and carbon dioxide gas.
The reactive metals form very stable carbonates and so they require a very high temperature to decompose. On the other hand, the unreactive metals form unstable carbonates and so they decompose at a relatively low temperature.
Thus, calcium carbonate on heating will give carbon dioxide gas and calcium oxide as residue.
${\text{CaC}}{{\text{O}}_{\text{3}}}\left( {\text{s}} \right)\xrightarrow{\Delta }{\text{CaO}}\left( {\text{s}} \right){\text{ + C}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right)$

Note:
The reaction of metal carbonates with acids can be used to test unknown solutions if they are acidic. The test is done by simply adding a sodium carbonate solution to the solution and if carbon dioxide is given off, the solution is acidic.
It is also used to test the presence of carbonate ions. If an acid is added to a solution and bubbles of carbon dioxide are given off, then the solution contains carbonate ions.