Exams › JEE Main › Chemistry

Given the standard reduction potentials: Fe2+ + 2e- -> Fe; E° = -0.41 V Ag+ + e- -> Ag; E° = +0.80 V O2 + 2H2O + 4e- -> 4OH-; E° = +0.40 V A bar of silver is joined by a wire to an iron pipe buried underground. What is the expected outcome?

1. The silver would corrode, a current would flow in the wire, and O2 would be reduced at the iron pipe surface.
2. The silver would corrode, a current would flow in the wire, and Fe2+ would be reduced at the iron pipe surface.
3. The iron pipe would corrode, a current would flow in the wire, and Ag+ would be reduced at the silver surface.
4. The iron pipe would corrode, no current would flow in the wire, and O2 would be reduced at the iron pipe surface.

Correct answer: The iron pipe would corrode, a current would flow in the wire, and Ag+ would be reduced at the silver surface.

Solution

Iron (E° = -0.41 V) is much more easily oxidized than silver (E° = +0.80 V). When the two are connected, a galvanic cell forms: iron is the anode and corrodes, while reduction occurs at the silver (cathode). Since the electrodes have different potentials, a net cell emf drives a current through the wire. At the silver cathode, the species with high reduction potential present (Ag+ from any dissolved silver, in the option's framing) is reduced. Note this is harmful — it accelerates iron corrosion, unlike a sacrificial anode (e.g., Mg or Zn) which would protect the iron.

Related JEE Main Chemistry questions

• During electrolysis of an aqueous solution of dipotassium succinate, which gas is evolved at the electrodes?
• Which expression gives the equivalent conductance at infinite dilution of Al2(SO4)3, if Λ°Al3+ and Λ°SO4²− denote the equivalent conductances at infinite dilution of the corresponding ions?
• The standard emf of a Daniell cell is 1.10 V. What is the greatest amount of electrical work that can be extracted from this cell?
• During the recharging of a lead storage battery, which reaction takes place at the cathode?
• The limiting molar ionic conductivities of the ions X2+ and Y2− are 57 and 73, respectively. What will be the molar conductivity of the electrolyte formed by these ions?
• According to Kohlrausch’s law, at what condition does each ion contribute a fixed amount to the conductance of an electrolyte, irrespective of the other ion present?

⚔️ Practice JEE Main Chemistry free + battle 1v1 →