Question

Calcium and Barium bicarbonates are stable only in solution and decompose on removal of water to give carbonates.
Answer whether the above statement is True or False.

Answer 1

Thermodynamically stable compounds are favoured more than the compounds with higher energies. Hydrogen bicarbonates anions $\left( {HC{O_3}^ - } \right)$ in water can do hydrogen bonding with itself to form a stable dimer.

Complete step by step answer:
Calcium and Barium bicarbonates are soluble in water due to the fact that Calcium and Barium bicarbonates are dissolved in water, they undergo the process of solvation which is an attractive natured process to associate the molecules of solvent with the ions or molecules of solute. Since solvent is water, so, solvation will be termed as hydration. Dissolving ionic compounds in water leads to release of energy which is called hydration energy. This release of energy will stabilize the Calcium, and Barium bicarbonates compounds in water. On the other hand, when water is removed, the aqueous form will convert to crystalline form. In crystalline form, the lattice energy of the carbonate is more than the bicarbonate, and lattice energy is directly proportional to stability of a substance, so, Calcium and Barium bicarbonates will decompose to give carbonates.
The reaction involved in it is:
$M{\left( {HC{O_3}} \right)_2}\left( {aq} \right) \to C{O_2}\left( g \right) + {H_2}O\left( l \right) + MC{O_3}\left( s \right)$
here $M$ is the Group $2$ metal.
Hence, the above given statement is true.

Note:
Thermal stability of Calcium bicarbonate is more than Barium bicarbonate because thermal stability is directly proportional to polarising power of cations, and the smaller the cation, the greater is the polarising power it has. Since, Calcium is smaller than Barium, so it has more polarising power.