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

- In potentiometric titration, the salt bridge plays a crucial role in maintaining the electrical neutrality between the reference and the indicator electrodes without allowing mixing of their respective solutions.
- Statement (i) is correct: The salt bridge prevents contamination between the reference electrode (such as calomel or silver-silver chloride) and the test (analyte) solution by providing an ionic connection.
- Statement (iv) is also correct: Salt bridges are often prepared using electrolytes such as KCl or KNO$_3$ , and are solidified with 3% agar or gelatin to prevent flow and mixing of liquids while maintaining conductivity.
- Statement (ii) is incorrect: Reference electrodes require a salt bridge for proper functioning in many setups.
- Statement (iii) is incorrect: Although the salt bridge minimizes the effect on test solution composition, it still contributes ions and hence has some effect.

Answer 2

The question asks which combination of statements about the role of a salt bridge in potentiometric titration is correct. A salt bridge in this setup connects the reference electrode to the test (analyte) solution while keeping the two physically separate, so let's look at what that separation actually accomplishes.

1. Prevent contamination of reference electrode to test solution (Statement I): This is one of the two primary jobs of a salt bridge. It stops the internal filling solution of the reference electrode (commonly saturated KCl) from mixing directly with the analyte, which would otherwise change the reference electrode's own potential and the composition of the test solution.
2. Only I: This undercounts the role of the salt bridge. A salt bridge does more than block contamination; it also provides a controlled path for ionic conduction between the two solutions, so limiting the correct answer to statement I alone leaves out a second true function.
3. I and III: Besides preventing contamination, a properly designed salt bridge (using nearly equal-mobility ions such as K⁺ and Cl^- or NO₃^-) minimizes the liquid junction potential that would otherwise build up where two different electrolyte solutions meet. Both of these functions, preventing contamination and minimizing junction potential, are genuinely true, which is why this combination fits.
4. I and IV: While statement I holds, pairing it with a statement claiming the salt bridge has essentially no influence on the test solution's composition overstates its inertness; a salt bridge does contribute a small, controlled ion leakage, so this pairing is not the accurate combination.

Preventing reference-electrode contamination and minimizing the liquid junction potential are the two roles genuinely and unambiguously served by a salt bridge in potentiometric titration.

Therefore, the correct answer is I and III.