Question

Arrange $Na^{+}$, $Mg^{2+}$ and $Al^{3+}$ in increasing order of energy of hydration

• A. $Na^{+} < \, Mg^{2+} < \, Al^{3+}$
• B. $Al^{3+} < \, Mg^{2+} < \, Na^{+}$
• C. $Al^{3+} < \, Na^{+} < \, Mg^{2+}$
• D. $Mg^{2+} < \, Al^{3+} < \, Na^{+}$

Answer 1

Answer: (A)

The hydration enthaplies (ie, energies of hydration) of metal ions decreases with increase in ionic radii. Because of the smaller size of $Al ^{3+}$ than $Mg ^{2+}$ and $Na ^{+}$, its energy of hydration is larger than both these ions.

The order of heat of hydration is

$Al ^{3+} > Mg ^{2+} > Na ^{+}$