Question: 81: Which one of the following is not a calcination reaction?
(1) \mathrm{ZnCO}_{3} \xrightarrow{\Delta} \mathrm{ZnO}+\mathrm{CO}_{2}
(2) \mathrm{Fe}_{2} \mathrm{O}_{3} \cdot x \mathrm{H}_{2} \mathrm{O} \xrightarrow{\Delta} \mathrm{Fe}_{2} \mathrm{O}_{3}+\mathrm{xH}_{2} \mathrm{O}
(3) \mathrm{CaCO}_{3} \cdot \mathrm{MgCO}_{3} \xrightarrow{\Delta} \mathrm{CaO}+\mathrm{MgO}+2 \mathrm{CO}_{2}
(4) \mathrm{CaCO}_{3}+2 \mathrm{HCl} \xrightarrow{\Delta} \mathrm{CaCl}_{2}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2}
Answer: Option (4)
Explanation:
Calcination is the process of heating an ore or compound in the absence or limited supply of air to bring about thermal decomposition,
usually converting carbonates or hydrated oxides into oxides by removing volatile substances like
\mathrm{CO}_{2} or \mathrm{H}_{2}\mathrm{O}.
In option (1), zinc carbonate decomposes on heating to form zinc oxide and carbon dioxide,
which is a typical calcination reaction.
In option (2), hydrated ferric oxide loses water on heating to form anhydrous ferric oxide.
This is also a calcination process.
In option (3), calcium magnesium carbonate decomposes on heating to give calcium oxide,
magnesium oxide, and carbon dioxide. This is another example of calcination.
In option (4), calcium carbonate reacts with hydrochloric acid to form calcium chloride, water,
and carbon dioxide. This is an acid–carbonate reaction, not thermal decomposition in the absence of air.
Hence, it is not a calcination reaction.