Question

Balance the following redox reactions by ion-electron method: 
(a)MnO₄^- _(aq) + I ^- _(aq) → MnO_2(s) + I₂(s) (in basic medium)
(b) MnO₄^- _(aq) + SO_2(g) → Mn₂⁺_(aq) +HSO₄^- _(aq) (in acidic solution)
(c) H₂O_2(aq)+Fe₂⁺_(aq) → Fe₃⁺ _(aq) + H₂O (l) (in acidic solution)
(d) Cr₂O₇^2-+ SO_2(g) → Cr³⁺ _(aq) +SO₄^2- _(aq) (in acidic solution)

Answer 1

(a) In basic medium

Reaction: \(\ce{MnO4^- (aq) + I^- (aq) -> MnO2 (s) + I2 (s)}\)

Balanced by ion–electron method (basic medium):

\[ \ce{2 MnO4^- + 6 I^- + 4 H2O -> 2 MnO2 + 3 I2 + 8 OH^-} \]

(b) In acidic medium

Reaction: \(\ce{MnO4^- (aq) + SO2 (g) -> Mn^{2+} (aq) + HSO4^- (aq)}\)

Balanced in acidic solution:

\[ \ce{2 MnO4^- + 5 SO2 + 2 H2O -> 2 Mn^{2+} + 5 HSO4^- + 3 H^+} \]

(c) In acidic medium

Reaction: \(\ce{H2O2 (aq) + Fe^{2+} (aq) -> Fe^{3+} (aq) + H2O (l)}\)

Balanced in acidic solution:

\[ \ce{H2O2 + 2 Fe^{2+} + 2 H^+ -> 2 Fe^{3+} + 2 H2O} \]

(d) In acidic medium

Reaction: \(\ce{Cr2O7^{2-} + SO2 (g) -> Cr^{3+} (aq) + SO4^{2-} (aq)}\)

Balanced in acidic solution:

\[ \ce{Cr2O7^{2-} + 3 SO2 + 2 H2O -> 2 Cr^{3+} + 3 SO4^{2-} + 4 H^+} \]