Question

consider the redox reaction below.
zn(s) + 2hcl(aq) ——→ zncl₂(aq) + h₂(g)
which half reaction correctly describes the oxidation that is taking place?
∘ zn²⁺(s) + 2e⁻(aq) ——→ zn(s)
∘ zn(s) ——→ zn²⁺(aq) + 2e⁻
∘ 2h⁺ + 2e⁻ ——→ h₂
∘ h₂ + 2e⁻ ——→ 2h⁺

Explanation:

1. Recall the definition of oxidation: Oxidation is the loss of electrons (increase in oxidation state).
2. Analyze the oxidation state of Zn: In $\ce{Zn(s)}$, the oxidation state of Zn is 0. In $\ce{ZnCl2(aq)}$, the oxidation state of Zn is +2. So Zn is being oxidized (losing electrons).
3. Check the half - reactions:

• For the first option $\ce{Zn^{2+}(s) + 2e^-(aq) -> Zn(s)}$, this is a reduction (gain of electrons) of $\ce{Zn^{2+}}$, not oxidation of Zn.
• For the second option $\ce{Zn(s) -> Zn^{2+}(aq) + 2e^-}$, Zn is going from an oxidation state of 0 to +2, and it is losing 2 electrons. This is an oxidation half - reaction.
• For the third option $\ce{2H^+ + 2e^- -> H2}$, this is a reduction (gain of electrons) of $\ce{H^+}$, not related to the oxidation of Zn.
• For the fourth option $\ce{H2 + 2e^- -> 2H^+}$, this is an oxidation of $\ce{H2}$ (losing electrons), but the question is about the oxidation of Zn in the given redox reaction.

Answer:

B. $\ce{Zn(s) -> Zn^{2+}(aq) + 2e^-}$