Question

Balance the following redox reaction occurring in basic solution.
I−(aq)+MnO−4(aq)→I2(aq)+MnO2(s)

Express your answer as a chemical equation. Identify all of the phases in your answer.

Answer 1

Answer –

We are given redox reaction –

I^-(aq) + MnO₄^- (aq) ------> I₂(aq) + MnO₂(s)

So first we need to determine the oxidation half reaction and reduction half reaction

Step 1) Assign the oxidation state to each element and write the two half reaction

I^-(aq) + MnO₄^- (aq) ------> I₂(aq) + MnO₂(s)

Mn = +7                              Mn = +4

O = -2                                  O = -2

I = -1                                    I = 0

So Mn get reduced and I gets oxidized

So,

                         I^-(aq) ------> I₂(aq) ………oxidation half reaction

                        MnO₄^-(aq) ----> MnO₂(s) ……….reduction half reaction

Step 2) Balance the element other than O and H

                       2 I^-(aq) ------> I₂(aq)

                       MnO₄^-(aq) ----> MnO₂(s)

Step 3) Balance the O by adding 1 H₂O for 1 O

                       2 I^-(aq) ------> I₂(aq)

                  MnO₄^-(aq) ----> MnO₂(s) + 2H₂O(l)

Step 4) Balance the H by adding H⁺

                         2 I^-(aq) ------> I₂(aq)

   MnO₄^-(aq) + 4H⁺(aq) ----> MnO₂(s) + 2H₂O(l)

Step 5) Balance the charge by adding electron

                                2 I^-(aq) ------> I₂(aq) + 2e^-

MnO₄^-(aq) + 4H⁺(aq) + 3e^- ----> MnO₂(s) + 2H₂O(l)

Step 6) Balance the electron in both half reaction – Multiply by reduction half reaction by 2 and oxidation half by 3

                                6 I^-(aq) ------> 3 I₂(aq) + 6e^-

2 MnO₄^-(aq) + 8H⁺(aq) + 6e^- ----> 2 MnO₂(s) + 4H₂O(l)

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6 I^-(aq) + 2 MnO₄^-(aq) + 8H⁺ ----->3 I₂(aq) + 2 MnO₂(s) + 4H₂O(l)

Now we need to added OH^- from both side as the number of H⁺ present in the reaction

6 I^-(aq) + 2 MnO₄^-(aq) + 8H⁺ + 8OH^-(aq)----->3 I₂(aq) + 2 MnO₂(s) + 4H₂O(l) + 8OH^-(aq)

6 I^-(aq) + 2 MnO₄^-(aq) +8H₂O(l) ----->3 I₂(aq) + 2 MnO₂(s) + 4H₂O(l) + 8OH^-(aq)

6 I^-(aq) + 2 MnO₄^-(aq) +4H₂O(l) ----->3 I₂(aq) + 2 MnO₂(s) + 8OH^-(aq)

So balanced redox reaction in basic medium is –

6 I^-(aq) + 2 MnO₄^-(aq) +4H₂O(l) ----->3 I₂(aq) + 2 MnO₂(s) + 8OH^-(aq)