Question

The variation of molar conductivity with concentration of an electrolyte (X) in aqueous solution is shown in the given figure.

The electrolyte X is :

• A. HCl
• B. \(\mathrm{CH_3COOH}\)
• C. NaCl
• D. \(\mathrm{KNO_3}\)

Hint:

The graph shows molar conductivity rising very steeply as the solution gets more dilute (\(\sqrt{c}\to 0\)), which is the behaviour of a weak electrolyte; strong electrolytes give a nearly straight, gently sloping line.

Answer 1

The Correct Option is B

For strong electrolytes, \(\Lambda_m = \Lambda_m^{0} - A\sqrt{c}\) (Debye-Huckel-Onsager), so the plot of \(\Lambda_m\) against \(\sqrt{c}\) is a straight line with a small negative slope.
For weak electrolytes, \(\Lambda_m\) is low at ordinary concentrations and rises very sharply at low concentration because the degree of dissociation \(\alpha\) approaches 1 on dilution; the curve is steep near \(\sqrt{c} \to 0\) and cannot be extrapolated linearly to \(\Lambda_m^{0}\).
The given graph is of the second type, so X is a weak electrolyte. HCl, NaCl and \(\mathrm{KNO_3}\) are strong electrolytes, while \(\mathrm{CH_3COOH}\) is a weak acid.
Answer: (2) \(\mathrm{CH_3COOH}\)