Question

The hydration energy of $M{g^{2 + }}$ is:
A.More than that of $M{g^{3 + }}$ ion
B.More than that of $N{a^ + }$ ion
C.More than that of $A{l^{3 + }}$ ion
D.More than that of $B{e^{2 + }}$ ion

Answer 1

Hint: Hydration energy is also known as hydration enthalpy. It is basically the amount of energy that is released when one mole of ion undergoes hydration. It is one component in the quantitative analysis of solvation.

Complete step by step answer:
-In simple words, hydration enthalpy or hydration energy is described as the amount of energy released on dilution of one mole of gaseous ions. It may be considered as the enthalpy of solvation with the solvent being water.
-Further, the magnitude of hydration enthalpy depends on the charge density of the ions. -The charge density is more for smaller ions and hence the smaller ions have higher values of hydration enthalpy. Moreover, the higher the charge density, the higher will be the force of attraction between the ion and the water polar end. This makes the value of hydration enthalpy higher in smaller ions. The alkali metals are highly hydrated and the extent of hydration further decreases down the group.
-So, the hydration energy of $M{g^{2 + }}$ is more than that of $N{a^ + }$ ion because the hydration energy increases with the charge on the cation and decreases as the size of the cation increases.

Hence, option B is correct.

Note:
The application of enthalpy of hydration is found in the reaction of cement with water. The reaction being exothermic releases a large amount of heat and this heat further becomes significant in mass construction like building dams and big structures.