Question

Agar – Agar is used in salt bridge since it is:
A. An electrolyte
B. A non-electrolyte
C. An inert electrolyte
D. A solid

Answer 1

Hint: A salt-bridge is a laboratory device which is used in an electrochemical cell to connect the oxidation and reduction half cells. It basically maintains the electrical neutrality within the internal circuit so that the reaction does not reach its equilibrium rapidly.

Complete solution:
Agar – agar is a semisolid, jelly like substance which is filled in the U – tube forming the salt bridge between the oxidation half cell and the reduction half cell of a Galvanic cell.
It is used because it is a nonelectrolyte, which means it does not dissociate to produce ions. Hence, there are no ions present for migration. Also, it prevents the intermixing of the two fluids present on the two sides of the salt bridge due to its gel nature, which might occur otherwise.
Salt bridge actually contains a relatively inert electrolyte like Potassium Chloride or Potassium Nitrate, which are gelified in the agar-agar medium. These inert electrolytes are chosen in a way such that they do not react with the chemicals used in the half cells.
If no salt bridge had been used, the solution of one half cell would have accumulated positive ions and the other would have accumulated negative ions, which would have resulted in no further reaction, and hence, no electricity would be produced by the cell.

Therefore, the correct answer is option (B).

Additional information:
The salt bridge that we generally talk about is a glass-tube salt bridge in which there is a U-tube filled with gelified relatively inert electrolyte. However, there is another type of salt bridge called Filter paper bridge in which there is no gel medium used. Rather, the filter paper is soaked in the relatively inert electrolyte which serves as a solid medium of conduction.

Note:
Students generally confuse the agar-agar medium with the relatively inert electrolyte. Please keep in mind that the agar-agar does not dissociate being a non-electrolyte whereas the electrolyte does dissociate and maintains electrical neutrality within the internal circuit.