Chemistry · Electrochemistry · NEET
Zinc is the ANODE. Zinc metal is a stronger reducing agent than copper, so it loses electrons and gets oxidised: Zn -> Zn(2+) + 2e-. Oxidation always happens at the anode. Copper is the cathode, where Cu(2+) + 2e- -> Cu (reduction). Easy rule: AN-OX, RED-CAT (Anode = Oxidation, Reduction = Cathode).
As the cell runs, the zinc beaker builds up extra positive Zn(2+) ions and the copper beaker builds up extra negative SO4(2-) ions. This charge imbalance would stop the reaction. The salt bridge (a U-tube of KCl or NH4NO3 set in agar jelly) releases its own ions to cancel these charges, so both solutions stay neutral and current keeps flowing. It also completes the inner circuit without letting the two solutions mix.
Electrons flow through the outside wire from the zinc anode to the copper cathode (from negative to positive terminal outside the cell). Inside the cell, current is carried by ions moving through the salt bridge. Note: electrons never travel through the salt bridge, only ions do.
Zinc atoms turn into Zn(2+) ions and leave the rod to enter the solution, so the zinc rod slowly dissolves and loses mass. At the copper side, Cu(2+) ions from the solution take electrons and deposit as solid copper on the rod, so the copper rod gains mass.
In a galvanic cell like the Daniell cell, the anode is the NEGATIVE terminal and the cathode is the POSITIVE terminal. This is the opposite of an electrolytic cell. The anode is negative because electrons pile up there (from oxidation) and push out into the wire. In cell notation we always write the anode on the LEFT: Zn | Zn(2+) || Cu(2+) | Cu.
In the electrochemical (Daniell) cell Zn | ZnSO4 (0.01 M) || CuSO4 (1.0 M) | Cu, the emf is E1. When the concentration of ZnSO4 is changed to 1.0 M and that of CuSO4 to 0.01 M, the emf changes to E2. Which one is the correct relationship between E1 and E2? (Given RT/F = 0.059)
Zinc can be coated on iron to produce galvanized iron but the reverse is not possible. It is because
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The standard EMF is 1.1 V, measured when both Zn(2+) and Cu(2+) ions are at 1 mol/L (unit concentration) at 298 K. It comes from E°cell = E°cathode - E°anode = 0.34 - (-0.76) = 1.10 V.
Zn(s) + Cu(2+)(aq) -> Zn(2+)(aq) + Cu(s). Zinc is oxidised at the anode and copper ions are reduced at the cathode. This gives out energy, so it is spontaneous (E°cell is positive).
A U-tube filled with an inert salt like KCl or NH4NO3, set into a jelly using agar-agar. Its ions (K+ and Cl-, for example) move out to balance the charge in each beaker.
Not for long. Without the salt bridge (or a porous partition), charge builds up in each beaker within seconds and the current stops. The salt bridge keeps both solutions neutral so the reaction can continue.
Because it produces electricity from a spontaneous redox reaction by itself, without any outside power source. A cell that instead uses outside electricity to force a reaction is an electrolytic cell.
