Which of the following carbonates is the least soluble in water ?

Options

A. `CaCO_(3)`
B. `BaCO_(3)`
C. `MgCO_(3)`
D. `BeCO_(3)`

Answer

B

Explanation

All the carbonates of group 2 elements are isoluble in water an their solubility decreases down the group from Be to Ba.
Carbonate ion `(CO_(3)^(2-))` is quite large. Thus, relatively small variations in the sizes of the cations from `Be^(2+)` to `Ba^(2+)` do not make much difference. Hence, the lattice enthalpy of carbonates practically does not change as we move down the group. However, hydration enthalpies of the metal cations decreases from `Be^(2+)` to `Ba^(2+)` hence the solubilities of carbnates of group 2 elements decrease down the group on account of the decrease o hydration enthalpy of cations from `Be^(2+)` to `Ba^(2+)`
However, all the carbonates of alkaline earth metals are more soluble in the present of `CO_(2)` due to the formation of corresponding bicarbonates.:
`CaCO_(3)(s)+CO_(2)(g)+H_(2)O(I)toCa(HCO_(3))_(2)(aq.)`