Read the passage carefully and answer.
The molar conductivity of a solution at any given concentration is the conductance of the volume of solution containing one mole of electrolyte kept between two platinum electrodes with unit area of cross-section and at a distance of unit length. Both conductivity and molar conductivity change with the concentration of the electrolyte. Kohlrausch examined $Ʌ°_m$ values for a number of strong electrolytes and observed certain regularities. He noted that the difference in $Ʌ°_m$ of the electrolytes NaX and KX for any X is nearly constant. On the basis of the above observations, he enunciated the Kohlrausch law of independent migration of ions.
Identify electrolyte A and B in the given image.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A is a weak electrolyte, B is a strong electrolyte.
The graph illustrates how different types of electrolytes behave when their solutions are diluted:
- Electrolyte B (Strong Electrolyte): The molar conductivity of strong electrolytes like $KCl$ increases slowly with dilution. As seen in the graph, it follows a linear relationship that can be extrapolated to zero concentration (point C) to find the limiting molar conductivity ($\Lambda_m^\circ$). This behavior is described by the Debye-Hückel-Onsager equation:
- $\Lambda_m = \Lambda_m^\circ - A \sqrt{c}$
- Electrolyte A (Weak Electrolyte): Weak electrolytes like acetic acid ($CH_3COOH$) show a very sharp increase in molar conductivity at low concentrations. This happens because dilution significantly increases the degree of dissociation ($\alpha$) of the electrolyte. Because the curve becomes almost parallel to the y-axis at very low concentrations, its limiting molar conductivity cannot be determined by simple extrapolation.
- Point C: This represents the limiting molar conductivity ($\Lambda_m^\circ$), the molar conductivity when the concentration of the electrolyte approaches zero (infinite dilution).
Correct Answer: A is a weak electrolyte, B is a strong electrolyte.