Question

Conductivity of CH\(_3\)COOH decreases on dilution. 

Hint:

Weak electrolytes like acetic acid dissociate partially, and dilution reduces the number of ions in solution, causing a decrease in conductivity.

Answer 1

The conductivity of acetic acid (CH₃COOH) decreases on dilution because it is a weak electrolyte that ionizes only partially in solution. This behavior can be understood by looking at the properties of weak electrolytes.

1. Weak Electrolyte Behavior:

Acetic acid is a weak electrolyte, meaning that it does not fully ionize in solution. The ionization of acetic acid in water is represented as: \[ \text{CH}_3\text{COOH} (aq) \rightleftharpoons \text{CH}_3\text{COO}^- (aq) + \text{H}^+ (aq) \] This reaction is reversible, and only a small fraction of acetic acid molecules dissociate into ions.

2. Effect of Dilution:

When acetic acid is diluted with water, the concentration of both dissociated ions (\( \text{CH}_3\text{COO}^- \) and \( \text{H}^+ \)) decreases. Since conductivity (\( \kappa \)) depends on the number of ions in the solution, the conductivity decreases as the solution becomes more dilute.

In the case of weak electrolytes like acetic acid, dilution shifts the equilibrium of the ionization reaction to the right, meaning more acetic acid dissociates. However, despite the increase in ionization, the overall number of ions still decreases with dilution, which results in a net decrease in conductivity.

3. Explanation of Decreased Conductivity:

As the solution is diluted, the number of dissociated ions decreases, reducing the electrical conductivity. This is because the conductivity is directly proportional to the concentration of ions in solution. Therefore, even though the ionization of acetic acid might increase slightly upon dilution, the overall ion concentration is lower, leading to reduced conductivity.

Conclusion:

In summary, dilution of acetic acid decreases the conductivity because it is a weak electrolyte that ionizes partially. As the concentration of ions decreases, the overall conductivity of the solution decreases as well.