What is the standard emf of the cell Cu(s) | Cu2+(aq) || Au+(aq) | Au(s)?

• A. -1.35 V
• B. +2.03 V
• C. -2.03 V
• D. +1.35 V

Answer: (D)

The standard emf of a galvanic cell is the difference between the standard reduction potentials of the cathode and the anode: E°cell = E°cathode − E°anode. The electrode with the higher reduction potential is reduced at the cathode, while the other is oxidized at the anode.

In this cell, Au+/Au has the higher reduction potential (+1.69 V) and Cu2+/Cu has +0.34 V. So Au+/Au serves as the cathode and Cu2+/Cu serves as the anode. Therefore, E°cell = 1.69 V − 0.34 V = +1.35 V. The positive value indicates the reaction as written is spontaneous.