Question

Which one of the following alkaline earth metal ions has the highest ionic mobility in its aqueous solution?

• A. \(Be^{2+}\)
• B. \(Mg^{2+}\)
• C. \(Ca^{2+}\)
• D. \(Sr^{2+}\)

Answer 1

The Correct Option is D

The question asks us to identify which alkaline earth metal ion has the highest ionic mobility in its aqueous solution among the given options \(Be^{2+}\), \(Mg^{2+}\), \(Ca^{2+}\), and \(Sr^{2+}\).

1. Ionic mobility refers to the speed at which an ion can move through a solution under the influence of an electric field. It is influenced by the size of the ion and its charge density.
2. In aqueous solutions, ions are surrounded by water molecules (hydration). Smaller ions tend to have higher charge densities and thus attract more water molecules around them, leading to greater hydration.
3. The more an ion is hydrated, the larger its effective size in solution becomes, decreasing its mobility.
4. Among the alkaline earth metal ions given:
   • \(Be^{2+}\) is the smallest ion, hence it is highly hydrated and moves slower.
   • \(Mg^{2+}\) is also relatively small, leading to significant hydration.
   • \(Ca^{2+}\) and \(Sr^{2+}\), being larger, have lower charge densities and thus less hydration.
5. Therefore, between \(Ca^{2+}\) and \(Sr^{2+}\), \(Sr^{2+}\) is the largest and least hydrated ion among the options provided, resulting in the highest ionic mobility.

Hence, the ion \(Sr^{2+}\) has the highest ionic mobility in its aqueous solution.