Answer:
8OH⁻ + Cr³⁺ + 3Fe³⁺ → 3Fe²⁺ + CrO₄²⁻ + 4H₂O
is the balanced reaction
Explanation:
Cr³⁺ is oxidized to CrO₄²⁻ and Fe³⁺ is reduced to Fe²⁺
In basic medium, you complete with water where you have the highest value of oxygen. In the opposite side we add OH⁻ as many oxygens, we have.
8OH⁻ + Cr³⁺ → CrO₄²⁻ + 4H₂O + 3e⁻
Chromium increased the oxidation state from +3 to +6. It released 3 electrons.
Fe³⁺ + 1e⁻ → Fe²⁺
Iron decreased the oxidation state from +3 to +2, so it won an electron.
We multiply the second half reaction x3, to balance the e⁻
(Fe³⁺ + 1e⁻ → Fe²⁺)x3 → 3Fe³⁺ + 3e⁻ → 3Fe²⁺
We mix the half reactions:
8OH⁻ + Cr³⁺ + 3Fe³⁺ + 3e⁻ → 3Fe²⁺ + CrO₄²⁻ + 4H₂O + 3e⁻
We cancel the electrons, so the balance reaction is:
8OH⁻ + Cr³⁺ + 3Fe³⁺ → 3Fe²⁺ + CrO₄²⁻ + 4H₂O
