Question

Why the hydration energy of Ca2+ is less than that of Al3+

Answer 1

Answer:

Now Al3+ and Mg2+ are nearly same in size. But the charge density on Al3+ is more than Mg2+ due to +3 charge on Al compared to +2 charge on Mg. Hence, hydration energy of Al3+ is more than Mg2+.

Answer 2

Answer:

The hydration energy is dependent on the charge density of ions. The smaller the ion the more the charge density and hence the hydration energy is also more. Due to the higher charge density the attraction is more and due to this the size of the ion decreases.

In $Al^{3+}$ the charge density is more and so the ion is smaller than that of   $Ca^{2+}$. This is why the hydration energy of $Ca^{2+}$is lesser then that of $Al^{2+}$.

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