Question

How to balance MnO4-(aq) + I-(aq) - MnO2(s) + I2(s) in basic medium by half reaction?

(NCERT book, chem part 2, page 268, prob 8.10)

Answer 1

MnO4^- + I - ----> MnO2 + I2

first let us find oxidation no. of I

oxidation state of oxygen is alway -2 except in peroxides n other cases

charge on I is -1 so its oxidation no. is -1

hope you completely understood the concept

Answer 2

The Process to balance $MnO_{4}^{-} + I^{-} -- > MnO_{2} + I_{2}$ in basic medium by half reaction is described below:

• Treated independently from any reduction that takes place. When the chemicals involved in the reaction are dissolved in water, the half-reaction approach performs better than the oxidation-number method. In an aqueous solution, hydrogen ions or hydroxide ions are usually present because the solution is either acidic or basic.
• Typically, atoms first balance the half-reactions on their own. In the half-reactions, electrons are present.
• The number of electrons acquired and lost are then equalised, resulting in a balanced state. Recombining the two half-reactions is the final step.

The unbalanced equation is -

$MnO_{4}^{-} + I^{-} -- > MnO_{2} + I_{2}$

The oxidation half reaction-

$I^{-} -- > I_{2}$

The reduction half reaction-

$MnO_{4}^{-} -- > MnO_{2}$

Now, we are balancing the oxidation reaction,

$2I^{-} -- > I_{2} +2e^{-}$

Mn's oxidation number shifts from +7 to +4 during the reduction half process. To the reactant side of the reaction, add 3 electrons.

$MnO_{4}^{-} +3e^{-} -- > MnO_{2}$

By adding 4 hydroxide ions to the product side, the charge in the reduction part of the process is balanced.

$MnO_{4} + 3e^{-} -- > MnO_{2} + 4OH^{-}$

$MnO_{4} + 3e^{-} + 2H_{2}O -- > MnO_{2} + 4OH^{-}$

The half reactions of oxidation and reduction should be multiplied by three and two, respectively, to equalise the quantity of electrons.

$6I -- > 3I_{2} + 6e^{-}$

Now adding two half reaction to get the final reaction-

$2MnO_{4}^{-} +6I^{-} + 4H_{2} O_{2} -- > 2MnO_{2} +3I_{2} + 8OH^{-}$

Hence, this is the process to balance $MnO_{4}^{-} + I^{-} -- > MnO_{2} + I_{2}$ in basic medium by half reaction.

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