Question

Identify the substance oxidised reduced, oxidising agent and reducing agent for each of the following reactions: (a) 2AgBr (s) + C₆H₆O₂(aq) → 2Ag(s) + 2HBr (aq) + C₆H₄O₂(aq) (b) HCHO(l) + 2[Ag (NH₃)₂]⁺(aq) + 3OH⁻(aq) → 2Ag(s) + HCOO⁻(aq) + 4NH₃(aq) + 2H₂O(l) (c) HCHO(l) + 2 Cu²⁺(aq) + 5 OH⁻(aq) → Cu₂O(s) + HCOO⁻(aq) + 3H₂O(l) (d) N₂H₄(l) + 2H₂O₂(l) → N₂(g) + 4H₂O(l) (e) Pb(s) + PbO₂(s) + 2H₂SO₄(aq) → 2PbSO₄(s) + 2H₂O(l)

Accepted Answer

(a) In the reaction 2AgBr (s) + C₆H₆O₂(aq) → 2Ag(s) + 2HBr (aq) + C₆H₄O₂(aq), C₆H₆O₂ is oxidised to C₆H₄O₂ and acts as the reducing agent. AgBr is reduced to Ag and acts as the oxidising agent. (b) In HCHO(l) + 2[Ag (NH₃)₂]⁺(aq) + 3OH⁻(aq) → 2Ag(s) + HCOO⁻(aq) + 4NH₃(aq) + 2H₂O(l), HCHO is oxidised to HCOO⁻ and is the reducing agent. [Ag(NH₃)₂]⁺ is reduced to Ag and is the oxidising agent. (c) In HCHO(l) + 2 Cu²⁺(aq) + 5 OH⁻(aq) → Cu₂O(s) + HCOO⁻(aq) + 3H₂O(l), HCHO is oxidised to HCOO⁻ and is the reducing agent. Cu²⁺ is reduced to Cu₂O and is the oxidising agent. (d) In N₂H₄(l) + 2H₂O₂(l) → N₂(g) + 4H₂O(l), N₂H₄ is oxidised to N₂ and is the reducing agent. H₂O₂ is reduced to H₂O and is the oxidising agent. (e) In Pb(s) + PbO₂(s) + 2H₂SO₄(aq) → 2PbSO₄(s) + 2H₂O(l), Pb is oxidised to PbSO₄ and is the reducing agent. PbO₂ is reduced to PbSO₄ and is the oxidising agent. — By analyzing the change in oxidation states of elements in each reaction, we can identify the substances oxidised and reduced. The substance that gets oxidised (increase in oxidation state or loss of hydrogen) is the reducing agent, and the substance that gets reduced (decrease in oxidation state or gain of hydrogen) is the oxidising agent.

Explanation

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