Question

When a Zn²⁺/Zn electrode is connected to a SHE, the electrons flow from zinc electrode to hydrogen electrode but the flow of electrons is in opposite direction when a Cu²⁺/Cu electrode is connected to a SHE. Explain giving reasons.

Answer 1

1. When a copper electrode (Cu/Cu²⁺) is connected to an SHE, the current flows from the copper to the hydrogen electrode, which means electrons flow from the SHE to the copper.
2. This indicates that the hydrogen electrode acts as the anode (oxidation occurs), and the copper electrode acts as the cathode (reduction occurs), since copper has a higher standard reduction potential (+0.34 V) than hydrogen (0.00 V).
3. In contrast, when the zinc electrode (Zn/Zn²⁺) is connected to SHE, zinc undergoes oxidation, releasing electrons, and acts as the anode, while SHE acts as the cathode.
4. This is because zinc has a lower standard reduction potential (–0.76 V) than hydrogen.

5. In Cu/SHE, electrons flow from SHE to Cu. In Zn/SHE, electrons flow from Zn to SHE.

Therefore, the direction of electron flow is opposite in the copper and zinc electrodes when connected to the hydrogen electrode.