Calculate E°cell for the galvanic cell Zn(s) | Zn2+(aq) || Cl-(aq) | AgCl(s) | Ag(s).

• A. +1.20 V
• B. -1.20 V
• C. +0.98 V
• D. +0.54 V

Answer: (D)

Use standard electrode potentials to find the cell potential by identifying which half-reaction is reduced at the cathode and which is oxidized at the anode. The gallvanic cell potential is E°cell = E°red(cathode) − E°red(anode).

Here, the AgCl/Ag couple has E° ≈ +0.22 V for the reduction AgCl(s) + e− → Ag(s) + Cl− (1 M Cl−). The Zn2+/Zn couple has E° = −0.76 V for the reduction Zn2+ + 2e− → Zn(s). The AgCl/Ag couple is the higher reduction potential, so it serves as the cathode, and zinc is the anode.

Compute E°cell: 0.22 V − (−0.76 V) ≈ +0.98 V.

So the standard cell potential is about +0.98 V, indicating a spontaneous reaction under standard conditions. The overall reaction is Zn(s) + 2 AgCl(s) → Zn2+ (aq) + 2 Cl− (aq) + 2 Ag(s).