A displacement reaction occurs at a metallic electrode in a solution containing Cu2+ and Zn2+. If Zn is more reactive, which species is reduced and which is oxidized at the electrode?

• A. Cu2+ is reduced to Cu at the cathode, and Zn(s) is oxidized to Zn2+ at the anode
• B. Zn2+ is reduced to Zn at the cathode, and Cu is oxidized to Cu2+ at the anode
• C. Both Cu2+ and Zn2+ are reduced
• D. Both Cu2+ and Zn2+ are oxidized

Answer: (A)

The key idea is that in a displacement situation the more reactive metal tends to be oxidized, while the less reactive ion is reduced at the cathode. Zinc is more reactive than copper, so zinc metal loses electrons to become Zn2+. Those electrons are consumed to reduce Cu2+ to copper metal at the cathode. So the species reduced is Cu2+ (to Cu), and the species oxidized is Zn (to Zn2+). The half-reactions are Cu2+ + 2e- → Cu(s) at the cathode and Zn(s) → Zn2+ + 2e- at the anode.