Question

The graphical variation of molar conductivity \((\Lambda )\) against square root of molar concentration \((\sqrt{c})\) of certain electrolyte 'X' is linear with intercept on y axis. Identify X from following.

• A. \(\text{CH}_3\text{COOH}\)
• B. \(\text{NH}_4\text{OH}\)
• C. \(\text{HCOOH}\)
• D. \(\text{CH}_3\text{COONa}\)

Hint:

Only strong electrolytes give a straight line with a finite intercept on the molar conductivity axis.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
For a strong electrolyte the Debye-Huckel-Onsager equation applies: \(\Lambda_m = \Lambda_m^0 - A\sqrt{c}\). Plotting \(\Lambda_m\) against \(\sqrt{c}\) gives a straight line whose intercept on the y axis is \(\Lambda_m^0\).

Step 2: Weak electrolytes:
\(\text{CH}_3\text{COOH}\), \(\text{NH}_4\text{OH}\) and \(\text{HCOOH}\) are weak electrolytes. Their degree of dissociation rises sharply on dilution, so \(\Lambda_m\) rises steeply at low concentration and the curve cannot be extrapolated to a limiting value.

Step 3: Strong electrolyte:
\(\text{CH}_3\text{COONa}\) is a salt that dissociates completely, so it is a strong electrolyte and gives the linear plot with an intercept.

Final Answer:
The electrolyte X is sodium acetate, option (D). \[ \boxed{\text{CH}_3\text{COONa}} \]