Question

The hydration energy of $M{g}^{++}$ is larger than that of:

• A. $A{l}^{3+}$
• B. $N{a}^{+}$
• C. $B{e}^{++}$
• D. None of the above

Answer 1

The correct option is B $N{a}^{+}$

$M{g}^{2+}$ has the larger hydration energy, because hydration energy increases with the charge on the cation and decreases as the size of the cation increases. Therefore, answer is $N{a}^{+}$.

Theory:
Hydration energy:
Hydration enthalpies of alkaline earth metal ions decrease with increase in ionic size

$B{e}^{2+}>M{g}^{2+}>C{a}^{2+}>S{r}^{2+}>B{a}^{2+}$



Compounds of alkaline earth metals are more extensively hydrated than those of alkali metals.
e.g., $MgC{l}_2$ and $CaC{l}_2$ exist as $MgC{l}_2.6H_{2}O$ and $CaC{l}_2.6H_{2}O$
NaCl and KCl do not form such hydrates.