Given the following redox reaction, write out the half-reaction that occurs at the anode and the cathode.

Ni2+ (aq) + Mg (s) → Ni (s) + Mg2+(aq)

Question

Given the following redox reaction, write out the half-reaction that occurs at the anode and the cathode.

Ni2+ (aq) + Mg (s) → Ni (s) + Mg2+(aq)

BlackTom AI · Accepted Answer

Magnesium is oxidized from 0 to +2, so it loses electrons; nickel(II) is reduced from +2 to 0, so it gains electrons.

Relevant concepts:
- Oxidation is loss of electrons (increase in oxidation number); reduction is gain of electrons (decrease in oxidation number).
- The anode is where oxidation occurs; the cathode is where reduction occurs.
- Half-reactions must show electron transfer and be balanced for charge and atoms.

Step-by-step reasoning and intermediate steps:
1. Assign oxidation states:
   - Mg (s): 0
   - Mg2+ (aq): +2
   - Ni2+ (aq): +2
   - Ni (s): 0

2. Identify which species change oxidation state:
   - Mg: 0 → +2 (oxidation; electrons lost)
   - Ni: +2 → 0 (reduction; electrons gained)

3. Write the oxidation half-reaction (anode). Magnesium loses two electrons to become Mg2+:
   Mg (s) → Mg2+ (aq) + 2 e−

Check: atoms balanced (1 Mg each side); charge: left 0, right +2 + (2 × −1) = 0 → balanced.

4. Write the reduction half-reaction (cathode). Nickel(II) gains two electrons to form nickel metal:
   Ni2+ (aq) + 2 e− → Ni (s)

Check: atoms balanced (1 Ni each side); charge: left +2 + (2 × −1) = 0, right 0 → balanced.

5. Combine half-reactions: the 2 e− cancel, giving overall Mg (s) + Ni2+ (aq) → Mg2+ (aq) + Ni (s), which matches the given reaction.

Why the correct choice is correct:
- It correctly identifies Mg oxidation at the anode producing 2 e− and Ni2+ reduction at the cathode consuming 2 e−, with charge and atoms balanced.

Why other options are incorrect:
- Option 2 swaps anode/cathode (reversal of oxidation/reduction).
- Options 3 and 4 omit electrons, leaving half-reactions charge-unbalanced and chemically incorrect.
- Option 5 shows single-electron transfers; the actual change in oxidation states requires 2 e− each, so that option is incorrect.

Final confirmation: anode: Mg (s) → Mg2+ (aq) + 2e−; cathode: Ni2+ (aq) + 2e− → Ni (s). This matches the provided correct answer.

Given the following redox reaction, write out the half-reaction that occurs at the anode and the cathode. Ni2+ (aq) + Mg (s) → Ni (s) + Mg2+(aq)单项选择题

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