Q26 / 180 · COMEDK 2025 (10 May Shift 2) · Chemistry
Two statements, one Assertion and the other Reason are given. Choose the correct option.
Assertion: For strong electrolytes the plot of Molar conductivity versus Concentration gives a straight line with slope equal to +A and intercept equal to $\lambda_{\mathrm{m}}$.
Reason: For strong electrolytes, $\lambda_{\mathrm{m}}$ increases slowly with dilution due to increase in the distance between the ions and increase in ionic mobility
- ABoth Assertion and Reason are incorrect.
- BAssertion is correct but Reason is incorrect.
- Correct answerCAssertion is incorrect but Reason is correct.
- DBoth Assertion and Reason are correct.
Solution
The molar conductivity $\lambda_{m}$ of a strong electrolyte varies with concentration $C$ according to the Kohlrausch equation: $\lambda_{m} = \lambda_{m}^{\circ} - A\sqrt{C}$, where $\lambda_{m}^{\circ}$ is the molar conductivity at infinite dilution and $A$ is a constant.
The plot of $\lambda_{m}$ versus $\sqrt{C}$ is a straight line with a negative slope equal to $-A$ and an intercept equal to $\lambda_{m}^{\circ}$. The Assertion states the slope is $+A$ and the intercept is $\lambda_{m}$, which is incorrect.
For strong electrolytes, $\lambda_{m}$ increases slowly with dilution because the inter-ionic attractions decrease as the distance between the ions increases, leading to an increase in ionic mobility. Thus, the Reason is correct.
Answer: Assertion is incorrect but Reason is correct.
The plot of $\lambda_{m}$ versus $\sqrt{C}$ is a straight line with a negative slope equal to $-A$ and an intercept equal to $\lambda_{m}^{\circ}$. The Assertion states the slope is $+A$ and the intercept is $\lambda_{m}$, which is incorrect.
For strong electrolytes, $\lambda_{m}$ increases slowly with dilution because the inter-ionic attractions decrease as the distance between the ions increases, leading to an increase in ionic mobility. Thus, the Reason is correct.
Answer: Assertion is incorrect but Reason is correct.
Hence, the correct answer is option: 'C'.