Question

Saturated solution of \(KNO_3\) is used to make salt bridge because

• A. Velocity of \(K^+\) is greater than that of \(NO_3^-\)
• B. Velocity of \(NO_3^-\) is greater than that of \(K^+\)
• C. Velocity of both \(K^+\) and \(NO_3^-\) are nearly the same
• D. \(KNO_3\) is highly soluble in water

Hint:

Salt bridge electrolyte should have ions with nearly equal mobility to reduce liquid junction potential.

Answer 1

The Correct Option is C

Concept:
A salt bridge is used in an electrochemical cell to complete the circuit and maintain electrical neutrality. A good salt bridge electrolyte should have ions that move with nearly equal speeds. This helps to minimize liquid junction potential.

Step 1: Understand the function of salt bridge.
During cell reaction, ions are produced or consumed in the two half-cells. If charge imbalance develops, the cell reaction stops. The salt bridge supplies ions to maintain electrical neutrality.

Step 2: Why \(KNO_3\) is used.
In \(KNO_3\), the ions are: \[ K^+ \quad \text{and} \quad NO_3^- \] These ions have nearly equal ionic mobilities. So they move at nearly the same rate.

Step 3: Importance of equal ionic mobility.
If one ion moves much faster than the other, charge separation occurs near the junction. This creates liquid junction potential. To avoid this, ions with nearly equal speeds are preferred.

Step 4: Check the options.
Option (A) is incorrect because \(K^+\) is not selected because it moves much faster.
Option (B) is incorrect because \(NO_3^-\) is not selected because it moves much faster.
Option (C) is correct because both ions have nearly the same velocity.
Option (D) is true that \(KNO_3\) is soluble, but the main reason is nearly equal ionic mobility. Hence, the correct answer is: \[ \boxed{(C)\ \text{Velocity of both }K^+\text{ and }NO_3^-\text{ are nearly the same}} \]