Questions: Oxidation-Reduction Basics

Question 1

In the reaction Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s), which species is the oxidizing agent?

• A. Zn
• B. Cu²⁺
• C. SO₄²⁻
• D. ZnSO₄

Answer: (B)

Cu²⁺ is the oxidizing agent because it accepts electrons from Zn and is itself reduced to Cu(s). Zn loses electrons (is oxidized) and is therefore the reducing agent. SO₄²⁻ is a spectator ion — it neither gains nor loses electrons. A common error is labeling the species that gets oxidized as the oxidizing agent; the oxidizing agent causes oxidation in its partner by accepting those electrons, so it is the one that gets reduced.

Question 2

Oxidation generally involves a chemical reaction with oxygen gas.

• T. True
• F. False

Answer: False

The name 'oxidation' is historical — it was coined to describe combustion and rusting reactions involving O₂. The modern definition is simply the loss of electrons, which has nothing to do with oxygen. When Zn dissolves in HCl (Zn → Zn²⁺ + 2e⁻), zinc is oxidized but no oxygen is present. Reactions inside batteries and biological electron-transport chains are oxidation reactions with no O₂ involved.

Question 3

In a redox reaction, what is the relationship between the oxidizing agent and the process of reduction?

Model answer: The oxidizing agent is the species that gets reduced. It accepts electrons from the other reactant, causing that other species to be oxidized. The two roles are always paired: the oxidizing agent gains electrons (undergoes reduction), while the reducing agent loses electrons (undergoes oxidation). You cannot have one without the other.

The cross-naming is deliberate: an oxidizing agent causes oxidation in its partner by accepting those electrons — so the oxidizing agent itself is reduced. The mnemonic OIL RIG handles electron direction, but the key to agent labels is reading them as 'what does this species do to its partner, not to itself.' The oxidizing agent oxidizes the other species; by doing so, it gets reduced.