On adding copper metal to concentrated H2SO4, a colourless gas, sulfur dioxide (SO2), is released and the solution turns blue due to the formation of copper (II) sulfate (CuSO4).

The reaction can be represented as:

$$Cu (s) + 2H2SO4 (conc.) → CuSO4 (aq) + 2H2O (l) + SO2 (g)$$