Question

Balance the following redox equation.

Cu(s) + H⁺(aq) + SO₄²⁻(aq) → Cu²⁺(aq) + H₂O(l) + SO₂(g)

Answer 1

Cu in Cu has oxidation state of 0

Cu in Cu+2 has oxidation state of +2

So, Cu in Cu is oxidised to Cu+2

S in SO4-2 has oxidation state of +6

S in SO2 has oxidation state of +4

So, S in SO4-2 is reduced to SO2

Reduction half cell:

1 SO4-2 + 2e- --> 1 SO2

Oxidation half cell:

1 Cu --> 1 Cu+2 + 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.

1 SO4-2 + 1 Cu --> 1 SO2 + 1 Cu+2

Balance Oxygen by adding water

1 SO4-2 + 1 Cu --> 1 SO2 + 1 Cu+2 + 2 H2O

Balance Hydrogen by adding H+

1 SO4-2 + 1 Cu + 4 H+ --> 1 SO2 + 1 Cu+2 + 2 H2O

This is balanced chemical equation in acidic medium

SO4^-2 + Cu + 4 H+ --> SO₂ + Cu⁺² + 2 H₂O