Question

The dichromate ion oxidizes iron (II) to iron (III) in acid solution. Balance the equation:
Cr2O
2- + H3O
+ + Fe
2+ → Cr3+ + Fe
3+ + H2O, by the half-reaction method

Answer 1

Cr₂O₇^2- + H₃O⁺ + Fe²⁺ = Cr³⁺ + Fe³⁺ + H₂O

2Cr⁺⁶ + 6e = 2Cr⁺³    6      1

Fe⁺² – 1e = Fe⁺³        1      6

Therefore, the ionic equation has the form:

Cr₂O₇^2- + 14H₃O⁺ + 6Fe²⁺ = 2Cr³⁺ + 6Fe³⁺ + 21H₂O