Question

A weak electrolyte obeys Ostwald's dilution law. Select the correct statement(s).

• A. A decrease in concentration of salts shows an increase in its degree of dissociation $\left(\alpha \right)$.
• B. As $c\to 0$, the degree of dissociation $\left(\alpha \right)$ approaches unity.
• C. A plot of ${\alpha }^2$ versus $\frac{1}{c}$ gives a straight line with a slope equal to dissociation constant of weak electrolyte when $\alpha <0.05$.
• D. A plot of ${\alpha }^2$ versus $c$ gives a straight line with a slope equal to dissociation constant of weak electrolyte.

Answer 1

Answer: (A), (B), (C)

The correct options are
A A decrease in concentration of salts shows an increase in its degree of dissociation $\left(\alpha \right)$.
B As $c\to 0$, the degree of dissociation $\left(\alpha \right)$ approaches unity.
C A plot of ${\alpha }^2$ versus $\frac{1}{c}$ gives a straight line with a slope equal to dissociation constant of weak electrolyte when $\alpha <0.05$.

On dilution, the degree of dissociation increases with a decrease in concentration.

At infinite dilution i.e, $C\to 0$, the degree of dissociation is around unity.

When ${\alpha }^2$ is plotted against $\frac{1}{c}$ for $\alpha <0.05$, a straight line with slope equal to dissociation constant of weak electrolyte is obtained.

$K_a=C{\alpha }^2$ or ${\alpha }^2=\frac{K_a}{C}$