Answer to Question #161565 in General Chemistry for mike

Question

For the following equations, determine which are redox processes. For the ones that are redox reactions, identify the oxidizing agent and reducing agent.

a 2OH–(aq)  +  Cr2O72–(aq)   →  2CrO42–(aq)  +  H2O(l)

b I2O5(s)  +  5CO(g)  →  I2(s)  +  5CO2(g)

c PBr3(l)  +  3H2O(l)  → H3PO3(aq)  +  3HBr(aq)

d 2Hg2+(aq)  +  N2H4(aq)  →  2Hg(l)  + N2(g)  +  4H+(aq)

Answer 1

Solution:

a) 2OH⁻(aq) + Cr₂O₇²⁻(aq) → 2CrO₄²⁻(aq) + H₂O(ℓ)

The reaction is NOT redox because there is no change in oxidation number.

b) I₂O₅(s) + 5CO(g) → I₂(s) + 5CO₂(g)

The reaction is redox.

I₂O₅ is the oxidizing agent because it is reduced as the oxidation number of I decreases from +5 to 0.

CO is the reducing agent because it is oxidized as the oxidation number of C increases from 0 to +4.

c) PBr₃(ℓ) + 3H₂O(ℓ) → H₃PO₃(aq) + 3HBr(aq)

The reaction is NOT redox because there is no change in oxidation number.

d) 2Hg²⁺(aq) + N₂H₄(aq) → 2Hg(ℓ) + N₂(g) + 4H⁺(aq)

The reaction is redox.

Hg²⁺ is the oxidizing agent because it is reduced as the oxidation number of Hg decreases from +2 to 0.

N₂H₄ is the reducing agent because it is oxidized as the oxidation number of N increases from -2 to 0.