Consider the reactions: (a) H₃PO₂(aq) + 4 AgNO₃(aq) + 2 H₂O(l) → H₃PO₄(aq) + 4Ag(s) + 4HNO₃(aq) (b) H₃PO₂(aq) + 2CuSO₄(aq) + 2 H₂O(l) → H₃PO₄(aq) + 2Cu(s) + H₂SO₄(aq) (c) C₆H₅CHO(l) + 2[Ag (NH₃)₂]⁺(aq) + 3OH⁻(aq) → C₆H₅COO⁻(aq) + 2Ag(s) + 4NH₃ (aq) + 2 H₂O(l) (d) C₆H₅CHO(l) + 2Cu²⁺(aq) + 5OH⁻(aq) → No change observed. What inference do you draw about the behaviour of Ag⁺ and Cu²⁺ from these reactions?
From the given reactions, we can infer that Ag⁺ is a stronger oxidising agent than Cu²⁺.
In reactions (a) and (b), both Ag⁺ and Cu²⁺ are reduced to their respective metals by H₃PO₂, which acts as a reducing agent. However, in reactions (c) and (d), C₆H₅CHO reduces Ag⁺ to metallic silver, but fails to reduce Cu²⁺ (no change is observed). This shows that Ag⁺ can be reduced by a weaker reducing agent (C₆H₅CHO) compared to Cu²⁺. Therefore, the oxidising power of Ag⁺ is greater than that of Cu²⁺.
Explanation
The question tests the understanding of the relative strengths of oxidising agents. H3PO2 is a strong reducing agent as it reduces both Ag+ and Cu2+. C6H5CHO is a weaker reducing agent as it only reduces Ag+ but not Cu2+. Since Ag+ gets reduced by both strong and weak reducing agents, while Cu2+ is only reduced by a stronger reducing agent, Ag+ is a stronger oxidising agent than Cu2+.
Solution Steps
Step 1: Analyze reactions (a) and (b). H₃PO₂ reduces both Ag⁺ to Ag(s) and Cu²⁺ to Cu(s). Thus, H₃PO₂ acts as a strong reducing agent.
Step 2: Analyze reactions (c) and (d). C₆H₅CHO reduces Ag⁺ to Ag(s), but shows no reaction with Cu²⁺.
Step 3: Compare the oxidising behaviour. Since Ag⁺ is reduced by both H₃PO₂ and C₆H₅CHO, whereas Cu²⁺ is only reduced by H₃PO₂, it is concluded that Ag⁺ is a stronger oxidising agent than Cu²⁺.