Question

When copper carbonate is heated it releases brisk effervescence given by gas?
A.\[{\text{C}}{{\text{O}}_2}\]
B.\[{{\text{H}}_2}\]
C.\[{{\text{H}}_2}{\text{S}}\]
D.\[{\text{HCl}}\]

Answer 1

Hint: During a chemical reaction, when a gas is liberated out in the forms of a bubble in liquid reaction mixture, this is known as effervescence. Heating of calcium carbonate leads to formation of lime and a gas.

Complete answer:
Decomposition reactions are those reactions in which one compound is broken down to form more substance or we can say a single reactant breaks down to give simpler products known as decomposition reactions. Example of decomposition reaction are decomposition of calcium carbonate to calcium oxide and carbon dioxide \[\left( {{\text{CaC}}{{\text{O}}_{3\left( {\text{s}} \right)}} \to {\text{Ca}}{{\text{O}}_{\left( {\text{s}} \right)}} + {\text{C}}{{\text{O}}_{2\left( {\text{g}} \right)}}} \right)\] and heating of lead nitrate which causes emission of nitrogen dioxide \[\left( {2{\text{Pb}}{{\left( {{\text{N}}{{\text{O}}_3}} \right)}_2} \to 2{\text{Pb}}{{\text{O}}_{\left( {\text{s}} \right)}} + 4{\text{N}}{{\text{O}}_{2\left( {\text{g}} \right)}} + {{\text{O}}_{2\left( {\text{g}} \right)}}} \right)\] . These reactions are mostly endothermic reactions as decomposition heat is required.
In case of decomposition of calcium carbonate, calcium carbonate is broken down to produce carbon dioxide gas and calcium oxide. One mole of calcium carbonate has broken down to produce one mole each of calcium oxide and carbon dioxide.

Thus, the correct option is A.

Additional information:
Carbon dioxide readily reacts with alkalis forming the carbonate and if carbon dioxide is in excess, the hydrogen carbonate is formed. \[{\text{Ca}}{\left( {{\text{OH}}} \right)_{2\left( {{\text{aq}}} \right)}} + {\text{C}}{{\text{O}}_{2\left( {\text{g}} \right)}} \to {\text{CaC}}{{\text{O}}_{3\left( {\text{s}} \right)}} + {{\text{H}}_2}{{\text{O}}_{\left( {\text{l}} \right)}}\] and \[{\text{CaC}}{{\text{O}}_{3\left( {\text{s}} \right)}} + {{\text{H}}_2}{{\text{O}}_{\left( {\text{l}} \right)}} + {\text{C}}{{\text{O}}_{2\left( {\text{g}} \right)}} \to {\text{Ca}}{\left( {{\text{HC}}{{\text{O}}_3}} \right)_{2\left( {{\text{aq}}} \right)}}\] . This reaction accounts for the formation of temporarily hard water.

Note:
Carbon dioxide is produced in the laboratory by the action of dilute hydrochloric acid on marble chips. However, carbon dioxide is produced at industrial level as a byproduct during the manufacture of quicklime and in the fermentation process.