Q42 / 180 · COMEDK 2024 (Evening Shift) · Chemistry
Given below are 2 statements: Assertion and Reason. Choose the correct option.
Assertion: When Molar conductivity for a strong electrolyte is plotted versus $\sqrt{C}(\mathrm{~mol} / \mathrm{L})^{1 / 2}$, a straight line is obtained with intercept equal to Molar conductivity at infinite dilution for the electrolyte and Slope equal to $-\mathrm{A}$. All electrolytes of a given type have the same $\mathrm{A}$ value.
Reason: At infinite dilution, strong electrolytes of the same type will have different number of ions due to incomplete dissociation.
- Correct answerAAssertion is correct but Reason is incorrect statement.
- BAssertion is incorrect but Reason is correct statement.
- CBoth Assertion and Reason are incorrect statements.
- DBoth Assertion and Reason are correct and Reason is the correct explanation of Assertion.
Solution
The molar conductivity of a strong electrolyte varies with concentration according to the Kohlrausch equation: $\Lambda_m = \Lambda_m^{\circ} - A\sqrt{C}$. This equation represents a straight line when $\Lambda_m$ is plotted against $\sqrt{C}$, where the intercept is $\Lambda_m^{\circ}$ (molar conductivity at infinite dilution) and the slope is $-A$. The constant $A$ depends on the type of electrolyte (e.g., 1:1, 1:2, 2:1) and the solvent properties, meaning all electrolytes of a given type in a given solvent have the same $A$ value. Thus, the Assertion is correct.
The Reason states that at infinite dilution, strong electrolytes of the same type have a different number of ions due to incomplete dissociation. This is incorrect because strong electrolytes are considered to be completely dissociated at all concentrations, including at infinite dilution. Furthermore, the number of ions produced per formula unit is determined by the stoichiometry of the electrolyte, which is constant for a given type of electrolyte. Therefore, the Reason is an incorrect statement.
Answer: Assertion is correct but Reason is incorrect statement.
The Reason states that at infinite dilution, strong electrolytes of the same type have a different number of ions due to incomplete dissociation. This is incorrect because strong electrolytes are considered to be completely dissociated at all concentrations, including at infinite dilution. Furthermore, the number of ions produced per formula unit is determined by the stoichiometry of the electrolyte, which is constant for a given type of electrolyte. Therefore, the Reason is an incorrect statement.
Answer: Assertion is correct but Reason is incorrect statement.
Hence, the correct answer is option: 'A'.