Balance the following redox reactions by the ion-electron method in acidic medium.

$M n O_{4}^{-} (a q) + S O_{2} (g) \to M n^{2 +} (a q) + H S O_{4}^{-} (a q)$

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Solution

The unbalanced chemical equation is:

$M n O_{4}^{-} (a q) + S O_{2} (g) \to M n^{2 +} (a q) + H S O_{4}^{-} (a q)$

The oxidation half reaction is

$S O_{2} (g) + 2 H_{2} O (l) \to H S O_{4}^{-} (a q) + 3 H^{+} (a q) + 2 e^{-} (a q)$ .

The reduction half reaction is

$M n O_{4}^{-} (a q) \to M n^{(} 2 +) (a q)$ .

In the reduction half reaction, the oxidation number of Mn changes from +7 to +2. Hence, 5 electrons are added to LHS of the reaction.

$M n O_{4}^{-} (a q) + 5 e^{-} \to M n^{2 +} (a q)$

Charge is balanced in the reduction half reaction by adding 8 hydrogen ions to LHS.

$M n O_{4}^{-} (a q) + 5 e^{-} + 8 H^{+} (a q) \to M n^{2 +} (a q)$

To balance O atoms, 4 water molecules are added on RHS.

$M n O_{4}^{-} (a q) + 5 e^{-} + 8 H^{+} (a q) \to M n^{2 +} (a q) + 4 H_{2} O (l)$

To equalize the number of electrons, the oxidation half reaction is multiplied by 5 and the reduction half reaction is multiplied by 2.

$5 S O_{2} (g) + 10 H_{2} O (l) \to 5 H S O_{4}^{-} (a q) + 15 H^{+} (a q) + 10 e^{-} (a q)$

$2 M n O_{4}^{-} (a q) + 10 e^{-} + 16 H^{+} (a q) \to 2 M n^{2 +} (a q)$
Two half cell reactions are added to obtain a balanced equation.

$2 M n O_{4}^{-} (a q) + 5 S O_{2} (g) + 2 H_{2} O (l) \to 2 M n^{2 +} (a q) + 5 H S O_{4}^{-} (a q)$

Suggest Corrections

Similar questions

C r_{2} O_{7}^{2 -} + S O_{2} (g) \to C r^{3 +} (a q) + S O_{4}^{2 -} (a q)

M n O_{4}^{-} (a q) + I^{-} (a q) \to M n O_{2} (s) + I_{2} (s)

H_{2} O_{2} (a q) + F e^{2 +} (a q) \to F e^{3 +} (a q) + H_{2} O (l)

Balance the following redox reactions by ion-electron method:
$M n O_{4}^{-} (a q) + I^{-} (a q) \to M n O_{2} (s) + I_{2} (s)$ (in basic medium)

$M n O_{4}^{-} (a q) + S O_{2} (g) \to M n^{2 +} (a q) + (a q) H S O_{4 (a q)}^{-}$ (in acidic solution)

$H_{2} O_{2} (a q) + F e^{2 +} (a q) \to F e^{3 +} (a q) + H_{2} O (l)$ (in acidic solution)

$C r_{2} O_{7}^{2 -} + S O_{2} (g) \to C r^{3 +} (a q) + S O_{4}^{2 -}$ (aq) (in acidic solution)

M n O_{4}^{⊖} (a q) + I^{⊖} (a q) \to M n O_{2} (s) + I_{2} (s)

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