When the following oxidation-reduction reaction in acidic solution is balanced, what is the lowest whole-number coefficient for H2O, and on which side of the balanced equation should it appear?

MnO4 - (aq) + Br - (aq) →Mn2 + (aq) + Br2 (l)

Select one:

a. 1, reactant side

b. 2, product side

c. 8, product side

d. 16, reactant side

e. 4, product side

c. 8, product side

Explanation:

In order to balance a redox reaction we use the ion-electron method, which has the following steps:

Step 1: identify oxidation and reduction half-reaction.

Oxidation: MnO₄⁻ (aq) → Mn²⁺ (aq)

Reduction: Br⁻ (aq) → Br₂ (l)

Step 2: perform the mass balance adding H⁺ and H₂O where necessary

8 H⁺ (aq) + MnO₄⁻ (aq) → Mn²⁺ (aq) + 4 H₂O (l)

2 Br⁻ (aq) → Br₂ (l)

Step 3: perform the electrical balance adding electrons where necessary.

8 H⁺ (aq) + MnO₄⁻ (aq) + 5 e⁻ → Mn²⁺ (aq) + 4 H₂O (l)

2 Br⁻ (aq) → Br₂ (l) + 2 e⁻

Step 4: multiply both half-reactions by numbers that secure that the number of electrons gained and lost are the same.

2 * (8 H⁺ (aq) + MnO₄⁻ (aq) + 5 e⁻ → Mn²⁺ (aq) + 4 H₂O (l))

5 * (2 Br⁻ (aq) → Br₂ (l) + 2 e⁻)

Step 5: add both half-reactions side to side.

16 H⁺ (aq) + 2 MnO₄⁻ (aq) + 10 e⁻ + 10 Br⁻ (aq) → 2 Mn²⁺ (aq) + 8 H₂O (l) + 5 Br₂ (l) + 10 e⁻

16 H⁺ (aq) + 2 MnO₄⁻ (aq) + 10 Br⁻ (aq) → 2 Mn²⁺ (aq) + 8 H₂O (l) + 5 Br₂ (l)