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.
This SO2 gas gives out pungent smell and decolourizes KMnO4 and regenerates the acid consusmed in the first reaction, it is as follows:
The MnSO4 is colourless compound which is the main reason behind decolourization.
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