UPSC Combined Geo-Scientist, Mains · 2017 · Mains Paper I

Q1(a). Dichromate oxidation of iron

Question

Balance the following redox reaction in an acidic medium by the ion-electron method: Cr₂O₇²⁻ + Fe²⁺ → Cr³⁺ + Fe³⁺.

Cr₂O₇²⁻ + 14H⁺ + 6Fe²⁺ → 2Cr³⁺ + 7H₂O + 6Fe³⁺.

Reduction: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O.
Oxidation: Fe²⁺ → Fe³⁺ + e⁻. Multiply this half-reaction by six.
Add and cancel six electrons. Both sides contain 2 Cr, 7 O, 14 H and 6 Fe atoms, and total charge +24.

The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

CoversDichromate oxidation of ironRedox balancing