Question

Why do the conductivity of a solution decreases with dilution? Explain with reason.

Hint:

The conductivity of an electrolyte decreases with dilution due to the reduction in the number of ions per unit volume, which lowers the current-carrying capacity of the solution.

Answer 1

Effect of Dilution on Conductivity:
The conductivity of a solution decreases with dilution because as the solution is diluted, the number of ions in the solution per unit volume decreases. This leads to a decrease in the overall current-carrying capacity of the solution. The key factors involved are: 1. Ion Concentration:
Conductivity (\( \kappa \)) of a solution depends on the concentration of ions. As the concentration of ions decreases with dilution, the conductivity also decreases. The relationship is given by: \[ \kappa = \sum_{i} c_i \lambda_i \] Where: - \( \kappa \) is the conductivity,
- \( c_i \) is the concentration of the \( i^{th} \) ion,
- \( \lambda_i \) is the molar conductivity of the \( i^{th} \) ion. As dilution decreases the concentration \( c_i \), the conductivity \( \kappa \) decreases as well.
2. Ion Pairing:
At higher concentrations, ions tend to form ion pairs, which reduce the number of free ions in the solution, thus decreasing the conductivity. When a solution is diluted, ion pairing is minimized, but the total number of free ions decreases due to the lower concentration.
3. Decrease in Collision Frequency:
In concentrated solutions, ions are closer to each other and collide more often, which increases the chances of electrical conduction. As the solution is diluted, the ions are further apart, leading to fewer collisions and lower conductivity. Thus, with dilution, the total ion concentration and the ion mobility decrease, leading to a reduction in the overall conductivity of the solution.