For a Daniell cell (Zn|Zn2+||Cu2+|Cu), what is the standard cell potential E°cell given E°(Zn2+/Zn) = -0.76 V and E°(Cu2+/Cu) = +0.34 V?

• A. -1.10 V
• B. -0.42 V
• C. +1.10 V
• D. +0.42 V

Answer: (C)

The key idea is that the standard cell potential is found from the reduction potentials of the cathode and anode. In this Daniell cell, copper is reduced at the cathode and zinc is oxidized at the anode. So E°cell = E°red(cathode) − E°red(anode). Using E°red(cathode) = +0.34 V and E°red(anode) = −0.76 V gives E°cell = 0.34 − (−0.76) = +1.10 V. A positive value means the reaction is spontaneous under standard conditions. Equivalently, E°cell = E°red(cathode) + E°ox(anode) with E°ox(anode) = +0.76 V, yielding the same result. Therefore, the standard cell potential is +1.10 V.