Question

Balance each of the following redox reactions occurring in acidic aqueous solution.

A. I−(aq)+SO42−(aq)→H2SO3(aq)+I2(s)

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

Answer 1

I in I- has oxidation state of -1

I in I2 has oxidation state of 0

So, I in I- is oxidised to I2

S in SO4-2 has oxidation state of +6

S in H2SO3 has oxidation state of +4

So, S in SO4-2 is reduced to H2SO3

Reduction half cell:

SO4-2 + 2e- --> H2SO3

Oxidation half cell:

2 I- --> I2 + 2e-

Number of electrons is same in both half reactions.

So, balancing of electrons is not required. It's already balanced

Lets combine both the reactions.

SO4-2 + 2 I- --> H2SO3 + I2

Balance Oxygen by adding water

SO4-2 + 2 I- --> H2SO3 + I2 + H2O

Balance Hydrogen by adding H+

SO4-2 + 2 I- + 4 H+ --> H2SO3 + I2 + H2O

This is balanced chemical equation in acidic medium

Answer:

SO₄^2- + 2 I^- + 4 H⁺ --> H₂SO₃ + I₂ + H₂O