On heating Copper turnings with conc. H₂SO₄ a colorless gas with pungent smell is evolved which decolorizes acidified KMnO₄ solution. Identify the gas.

Copper being a metal is an excellent reducing agent. When copper turnings are heated with conc. H₂SO₄, the sulphur undergoes reduction and copper undergoes oxidation to evolve SO₂ gas.

Rxn:

This SO₂ gas gives out pungent smell and decolourizes KMnO₄ and regenerates the acid consusmed in the first reaction, it is as follows:

Rxn:

The MnSO₄ is colourless compound which is the main reason behind decolourization.