Question

In aqueous medium, cations like $ \text{H}^+ $ and $ \text{Li}^+ $ undergo hydration and exist in the hydrated form. Predict the numbers of water molecules surrounded with $ \text{H}^+ $ and $ \text{Li}^+ $ ions to form stable complex structure respectively.

• A. 1, 1
• B. 4, 6
• C. 4, 4
• D. 6, 6

Hint:

When analyzing hydration of ions, remember that smaller ions with higher charge densities tend to be surrounded by fewer water molecules. Larger ions, though still small, tend to attract more water molecules due to their larger size.

Answer 1

The Correct Option is B

Step 1: Understand the concept of hydration.
In aqueous solution, when cations like \( \text{H}^+ \) and \( \text{Li}^+ \) dissolve, they attract water molecules around them. This is called hydration. The number of water molecules surrounding the ion is determined by the size of the ion and its charge density. Smaller ions with higher charge densities can attract more water molecules.
Step 2: Hydration of \( \text{H}^+ \) ion.
The \( \text{H}^+ \) ion, also known as a proton, is extremely small with a high charge density. Because of this, it is surrounded by a small number of water molecules, typically around 4. These water molecules surround the ion in a tetrahedral arrangement.
Step 3: Hydration of \( \text{Li}^+ \) ion.
The \( \text{Li}^+ \) ion is also small but slightly larger than \( \text{H}^+ \). It also has a high charge density, but due to its larger size compared to \( \text{H}^+ \), it is surrounded by a greater number of water molecules, usually around 6. These water molecules arrange themselves around the \( \text{Li}^+ \) ion in a more symmetrical octahedral structure.
Step 4: Conclusion.
Thus, the number of water molecules surrounding \( \text{H}^+ \) is 4 and the number surrounding \( \text{Li}^+ \) is 6, which corresponds to option (B).