Sulphuric acid can behave as an oxidising agent, being itself reduced. This change is produced when it is heated with most other elements. Thus with carbon, C + 2H0SO4 = CO2 + 2SO2 + H2O; with sulphur, S + H2SO4= 3SO2 + H?O; with copper, mercury, iron, lead, silver, etc, a sulphate is formed, and sulphur dioxide is liberated ; this may be viewed as the reducing action of hydrogen, at the high temperature required for the reaction, thus: Cu + H2SO4 = CUSO4 + 2H and H2SO4 + 2H = 2H2O + SO2. The reduction goes further, and some sulphur is liberated, while copper sulphide is formed: CuSO4 +8H = CuS+ 4H2O ; H2SO4 + 6H «S + 4H,0.
Hydriodic, and to a less extent hydrobromic acid also, are oxidised by sulphuric acid: H2SO4 + 2HI = I2 + 2H2O + SO9; and alcohol and many other compounds of carbon have a reducing action on hot sulphuric acid.