The sBlock Elements - Result Question 29
####31. Which of the following compounds has the lowest melting point?
(a) $CaCl_2$
(b) $CaBr_2$
(c) $CaI_2$
(d) $CaF_2$
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Solution:
- (c) Melting point of metal halides decreases as the size of the halogen increases. The correct order is
$ CaF_2>CaCl_2>CaBr_2>CaI_2 $
(b) $Be^{2+}$ is very small, hence its hydration enthalpy is greater than its lattice enthalpy. Also, hydration energy decreases down the group.
(a) The magnitude of hydration energy for the hydroxides of alkaline earth metals remains almost same whereas lattice energy decreases appreciably down the group. Hence, solubility increases down the group.
(a) As the cation size increases down the group, the metal carbonates become more ionic in nature. Hence, the thermal stability increases as: $BeCO_3<MgCO_3<CaCO_3$.
The ionic character of group 1 carbonates is more than that of group 2, thus they possess more thermal stability. Hence, the correct order of thermal stability: $BeCO_3<MgCO_3<CuCO_3$ $<K_2 CO_3$.
