Chemistry · Redox Equilibrium · NEET
No. Electrons never pass through the salt bridge. Electrons flow only through the outer metallic wire, from the anode (zinc) to the cathode (copper). Inside the cell, only ions move, and they move through the salt bridge. This is the most common mix-up: wire carries electrons, salt bridge carries ions. Both together complete one full circuit.
As the cell runs, the anode solution builds up extra positive ions (Zn2+) and the cathode solution builds up extra negative ions (SO4^2-). This charge imbalance quickly stops the redox reaction. The salt bridge fixes this: its ions move into each beaker to cancel the extra charge, so both solutions stay neutral and current keeps flowing.
Anions (like Cl-) move toward the anode (the beaker gaining positive charge), and cations (like K+) move toward the cathode (the beaker gaining negative charge). Simple rule: negative ions go to the negative-electrode-source side to balance the positive build-up. This ion flow maintains neutrality in both half-cells.
These salts are picked because the speed of the positive ion almost equals the speed of the negative ion (nearly equal ionic mobility). This stops a junction potential building up at the contact point. They are also inert, meaning they do not react with the electrode solutions or take part in the cell reaction.
Agar-agar is a jelly. It holds the salt solution as a solid-like paste so the two solutions cannot physically mix or flow into each other, yet ions can still pass through the jelly. So it keeps the solutions separate while still allowing ionic contact. It does not conduct by itself; the dissolved KCl/NH4NO3 ions do the conducting.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
One, it completes the electrical circuit inside the cell by allowing ions to flow between the two half-cells. Two, it keeps both solutions electrically neutral by supplying ions that cancel the charge build-up at each electrode.
It is a U-tube filled with a concentrated solution of an inert salt (KCl or NH4NO3) that is set into a jelly using agar-agar. The jelly stops mixing but lets ions move.
Yes. This is its key job. Anions move to the anode half-cell and cations move to the cathode half-cell, so neither solution becomes charged and the reaction can keep going.
The reading drops to zero almost at once. Charge builds up in each beaker, the redox reaction stops, and no steady current flows.
So it does not react with the electrolytes or take part in the cell reaction. It only balances charge. That is why unreactive salts like KCl and NH4NO3 are used.
