Balance the following redox reactions by ion–electron method: (a) MnO₄⁻ (aq) + I⁻ (aq) → MnO₂ (s) + I₂ (s) (in basic medium) (b) MnO₄⁻ (aq) + SO₂ (g) → Mn²⁺ (aq) + HSO₄⁻ (aq) (in acidic solution) (c) H₂O₂ (aq) + Fe²⁺ (aq) → Fe³⁺ (aq) + H₂O (l) (in acidic solution) (d) Cr₂O₇²⁻ + SO₂ (g) → Cr³⁺ (aq) + SO₄²⁻ (aq) (in acidic solution)
Explanation
To balance redox reactions by the ion-electron method, we separate the reaction into oxidation and reduction half-reactions. We balance atoms and charges in each half-reaction. For acidic medium, we balance oxygen by adding H₂O and hydrogen by adding H⁺. For basic medium, we first balance as in acidic medium, then add OH⁻ to both sides for every H⁺, combining H⁺ and OH⁻ into H₂O. Finally, we multiply the half-reactions by appropriate integers to equalize the electrons transferred and add them together.