Write a balanced half-reaction for the reduction of dichromate ion Cr2O-27 to chromium ion Cr+3 in acidic aqueous solution. Be sure to add physical state symbols where appropriate.

14 H⁺ (aq) + Cr₂O₇²⁻ (aq) + 6 e⁻ → 2 Cr⁺³ + 7 H₂O (l)

Explanation:

Let's consider the half-reaction for the reduction of dichromate ion Cr₂O₇²⁻ to chromium ion Cr⁺³ in acidic aqueous solution.

Cr₂O₇²⁻ (aq) → Cr⁺³

Step 1: Perform the mass balance adding H₂O (l) and H⁺ (aq) where appropriate.

14 H⁺ (aq) + Cr₂O₇²⁻ (aq) → 2 Cr⁺³ + 7 H₂O (l)

Step 2: Perform the charge balance adding electrons where appropriate.

14 H⁺ (aq) + Cr₂O₇²⁻ (aq) + 6 e⁻ → 2 Cr⁺³ + 7 H₂O (l)