Question

Ion having highest hydration enthalpy among the given alkaline earth metal ions is:

• A. Be⁺²
• B. Mg⁺²
• C. Ca⁺²
• D. Ba⁺²

Answer 1

The Correct Option is A

The correct option is (A): Be\(^{2+}\)
Highly charged and smaller-sized metal ions have higher hydration energy. The hydration energy for the compact and charged ions is greater than the large-sized charged ions, in the alkaline earth metals. Therefore, the order of hydration energy in this group is Be\(^{2+}\)>Mg\(^{2+}\) >Ca\(^{2+}\)>Sr\(^{2+}\)>Ba\(^{2+}\).

Answer 2

Hydration energy is the amount of energy released when a hydrated ion is formed from a gaseous ion and water molecules. The magnitude of hydration energy depends on the size and charge of the ion.
As we move down a group of the periodic table, the size of the ions increases, and the hydration energy decreases. Therefore, among the given options, the ion with the highest hydration energy will be the smallest one with the highest charge.
Hence, the correct option is (A) Be⁺², which has the highest charge and is the smallest ion among the given options.
Answer. A

Answer 3

Hydration Enthalpy Analysis 

Hydration enthalpy is the energy released when one mole of gaseous ions is dissolved in water to form an infinitely dilute solution. It depends on the charge density of the ion. Higher the charge density, greater the hydration enthalpy.

Charge density is directly proportional to the charge of the ion and inversely proportional to the size of the ion.

Charge Density \( \propto \frac{\text{Charge}}{\text{Size}} \)

Since all the given ions have the same charge (+2), the hydration enthalpy will be inversely proportional to the size of the ion.

Hydration Enthalpy \( \propto \frac{1}{\text{Size}} \)

Down the group in the periodic table (from Be to Ba), the size of the alkaline earth metal ions increases. Thus, the hydration enthalpy decreases down the group. The order of hydration enthalpy is:

\( \text{Be}^{2+} > \text{Mg}^{2+} > \text{Ca}^{2+} > \text{Sr}^{2+} > \text{Ba}^{2+} \)

Conclusion:

\( \text{Be}^{2+} \) has the highest hydration enthalpy.

Answer 4

Hydration enthalpy is inversely proportional to the size of the ion, i.e., \[ \text{Hydration enthalpy} \propto \frac{1}{\text{size}}. \] As the size of the ion increases down the group, hydration enthalpy decreases. Therefore, the order of hydration enthalpy is: \[ \text{Be}^{2+} > \text{Mg}^{2+} > \text{Ca}^{2+} > \text{Sr}^{2+} > \text{Ba}^{2+}. \] Thus, Be\(^{2+}\) has the highest hydration enthalpy.