Question

An increase in equivalent conductance of a strong electrolyte with dilution is mainly due to

• A. Increase in both i.e. number of ions and ionic mobility of ions.
• B. Increase in number of ions
• C. Increase in ionic mobility of ions
• D. 100% ionization of electrolyte at normal dilution

Hint:

For strong electrolytes, dilution mainly increases ionic mobility. For weak electrolytes, dilution increases ionization.

Answer 1

The Correct Option is C

Concept:
Equivalent conductance is the conducting power of all ions produced by one gram equivalent of electrolyte. For electrolytes, equivalent conductance generally increases on dilution. The reason depends on whether the electrolyte is strong or weak.

Step 1: Understand strong electrolyte.
Strong electrolytes are almost completely ionized even at normal concentration. Examples: \[ NaCl,\quad KCl,\quad HCl \] So on dilution, the number of ions does not increase significantly because ions are already present.

Step 2: Effect of dilution on interionic attraction.
In concentrated solution, ions are closer to each other. They attract or repel each other, which reduces their free movement. On dilution, ions become farther apart. So interionic attractions decrease.

Step 3: Effect on ionic mobility.
When interionic attraction decreases, ions move more freely. Therefore: \[ \text{Ionic mobility increases} \] This increase in mobility increases equivalent conductance.

Step 4: Check the options.
Option (A) is incorrect for strong electrolytes because number of ions does not increase significantly.
Option (B) is incorrect for the same reason.
Option (C) is correct because ionic mobility increases on dilution.
Option (D) is not the main explanation for the increase with dilution. Hence, the correct answer is: \[ \boxed{(C)\ \text{Increase in ionic mobility of ions}} \]