Which one of the following cations has the maximum ionic mobility?

CONCEPT:

Ionic Mobility

• Ionic mobility refers to the ability of an ion to move through a solution under the influence of an electric field.
• It depends on several factors, including the size of the ion, its charge density, and the ease with which it can move through the solvent.
• Smaller ions with higher charge densities tend to have lower ionic mobilities due to stronger interactions with the solvent molecules, which result in the formation of a larger hydration shell.

EXPLANATION:

• The given options are divalent cations: Ba²⁺, Ca²⁺, Sr²⁺, Be²⁺.
• Among these cations, Ba²⁺ is the largest in size, while Be²⁺ is the smallest.
• Smaller ions (like Be²⁺) have high charge density, which leads to strong interactions with water molecules in the solution and the formation of a larger hydration shell.
• A larger hydration shell reduces the mobility of the ion because the effective size of the hydrated ion becomes much larger.
• On the other hand, larger ions (like Ba²⁺) have lower charge density and weaker interactions with the solvent, resulting in a smaller hydration shell and higher ionic mobility.
• Therefore, Ba²⁺ has the maximum ionic mobility among the given cations.

The correct Answer is Ba²⁺