Question

Order of limiting molar conductivities of these cations at 298 K is:

• A. \( H^+, \, \text{Ca}^{2+}, \, \text{Na}^+, \, \text{Li}^+, \, \text{K}^+, \, \text{Mg}^{2+} \)
• B. \( H^+, \, \text{Na}^+, \, \text{Ca}^{2+}, \, \text{Li}^+, \, \text{K}^+, \, \text{Mg}^{2+} \)
• C. \( H^+, \, \text{Li}^+, \, \text{Na}^+, \, \text{Ca}^{2+}, \, \text{Mg}^{2+}, \, \text{K}^+ \)
• D. \( H^+, \, \text{Li}^+, \, \text{K}^+, \, \text{Na}^+, \, \text{Mg}^{2+}, \, \text{Ca}^{2+} \)

Hint:

Limiting molar conductivity increases for smaller ions with higher charge and mobility.

Answer 1

The Correct Option is A

Limiting molar conductivity depends on the ion's size and charge. The order of limiting molar conductivities is generally given by: \[ H^+>\text{Ca}^{2+}>\text{Na}^+>\text{Li}^+>\text{K}^+>\text{Mg}^{2+} \] This is because \( H^+ \) has the highest conductivity due to its small size and ability to form hydronium ions in solution, while the highly charged ions like \( \text{Ca}^{2+} \) and \( \text{Mg}^{2+} \) have lower conductivities due to their larger sizes and stronger ion-ion interactions. Thus, the correct order is \( H^+, \, \text{Ca}^{2+}, \, \text{Na}^+, \, \text{Li}^+, \, \text{K}^+, \, \text{Mg}^{2+} \).