Question

Choose the correct statement in a potentiometric titration: Salt bridge is used as

• A. Prevent contamination of reference electrode to test solution
• B. Only I
• C. I and III
• D. I and IV

Hint:

Salt bridges ensure ionic continuity and prevent liquid junction potential while protecting the test solution from contamination.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
In potentiometric titration, the analyte solution and the reference electrode's internal solution have different compositions, and letting them mix freely would upset both the reference potential and the analyte. A salt bridge is the physical device that keeps electrical contact between the two while limiting this mixing.

Step 2: Key Formula or Approach:
A salt bridge is usually a tube filled with a concentrated, nearly-equal-mobility electrolyte such as KCl or KNO₃, often gelled with about 3 percent agar so it does not flow out. Its two jobs follow directly from this design: block direct mixing of the two solutions, and keep the potential drop at the junction as small and steady as possible.

Step 3: Detailed Explanation:
Because the salt bridge physically separates the reference electrode's filling solution from the test solution, it prevents the reference electrode from being contaminated by, or from contaminating, the analyte. At the same time, using ions of nearly equal mobility (K⁺ and Cl^-, or K⁺ and NO₃^-) means both ions diffuse across the junction at close to the same rate, which keeps the liquid junction potential small and reproducible instead of large and erratic. These are the two genuine, independent functions the salt bridge is serving.

Step 4: Final Answer:
The correct statements are that the salt bridge prevents contamination of the reference electrode and minimizes the liquid junction potential, corresponding to statements I and III.