To determine the oxidation half-reaction for the given chemical reaction:
[tex]\[
\text{Mg (s)} + \text{ZnCl}_2 \text{(aq)} \rightarrow \text{MgCl}_2 \text{(aq)} + \text{Zn (s)}
\][/tex]
we need to identify which substance is being oxidized, i.e., which substance loses electrons.
In oxidation-reduction (redox) reactions, oxidation is defined as the loss of electrons. Let's analyze the changes in oxidation states:
1. Identify the Initial and Final States:
- Magnesium (Mg) starts in the solid state as an elemental substance, so it has an oxidation state of 0.
- In the product, magnesium is in the form of [tex]\(\text{MgCl}_2\)[/tex], which means magnesium is now in the form of [tex]\(\text{Mg}^{2+}\)[/tex], indicating an oxidation state of +2.
- Zinc chloride ([tex]\(\text{ZnCl}_2\)[/tex]) contains zinc as [tex]\(\text{Zn}^{2+}\)[/tex] initially.
- In the product, zinc is in the solid state as elemental zinc (Zn), with an oxidation state of 0.
2. Determine the Changes in Oxidation States:
- Magnesium (Mg) goes from 0 to +2, indicating a loss of 2 electrons ([tex]\(2e^-\)[/tex]).
- Zinc ([tex]\(\text{Zn}^{2+}\)[/tex]) goes from +2 to 0, indicating a gain of 2 electrons ([tex]\(2e^-\)[/tex]).
3. Write the Half-Reactions:
- The oxidation half-reaction involves magnesium losing electrons:
[tex]\[
\text{Mg (s)} \rightarrow \text{Mg}^{2+} + 2e^-
\][/tex]
This represents the oxidation process since magnesium is losing electrons.
- The reduction half-reaction for zinc (which is not the answer we seek for this question) would be:
[tex]\[
\text{Zn}^{2+} + 2e^- \rightarrow \text{Zn (s)}
\][/tex]
Given this analysis, the correct oxidation half-reaction is:
[tex]\[
\text{Mg (s)} \rightarrow \text{Mg}^{2+} + 2e^-
\][/tex]
This corresponds to choice A. So, the answer is A.
