What is the role of salt bridge in Daniell cell?
(A) Maintain electrical neutrality
(B) Allow the flow of ions without mixing of the two half cell solutions.
(C) Oxidize all the species involved.
(D) Reduce all the species involved.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A) and (B) only
In a Daniell cell, zinc dips into \( \ce{ZnSO4} \) solution (anode, oxidation) and copper dips into \( \ce{CuSO4} \) solution (cathode, reduction). The two solutions are connected by a salt bridge, an inverted U-tube filled with a gel of agar-agar containing an inert electrolyte such as KCl or \( \ce{KNO3} \).
\( \displaystyle \text{Anode: }\ce{Zn -> Zn^2+ + 2e^-} \)
\( \displaystyle \text{Cathode: }\ce{Cu^2+ + 2e^- -> Cu} \)
\( \displaystyle \text{Cell reaction: }\ce{Zn + Cu^2+ -> Zn^2+ + Cu} \)
As the cell works, \( \ce{Zn^{2+}} \) ions build up in the anode solution and \( \ce{Cu^{2+}} \) ions are removed from the cathode solution. Ions from the salt bridge move into both solutions to balance these charges.
(A) Maintain electrical neutrality — Correct. Anions from the salt bridge move into the anode solution and cations into the cathode solution. Without this, charge would build up in each half cell and the current would stop almost at once.
(B) Allow the flow of ions without mixing of the two half cell solutions. — Correct. The ions moving through the bridge complete the internal circuit, while the gel keeps the two solutions apart. If they mixed, \( \ce{Cu^{2+}} \) would react directly with zinc and no current would flow through the external wire.
(C) Oxidize all the species involved. — Incorrect. Oxidation takes place only at the anode, where zinc loses electrons. The electrolyte in the salt bridge is inert and takes no part in the redox reaction.
(D) Reduce all the species involved. — Incorrect. Reduction takes place only at the cathode, and the electrons reach it through the external wire, not through the salt bridge.