The manganese compound so formed is very unstable, however, and breaks clown according to the equation
MnCl4 = MnCl2 + 2Cl.
Instead of using hydrochloric acid in the preparation of chlorine it will serve just as well to use a mixture of sodium chloride and sulphuric acid, since these two react to form hydrochloric acid. The following equations will then express the changes:
(1) 2NaCl + H2SO4 = Na2SO4 + 2HCl.
(2) MnO2 + 4 HCl = MnCl2 + 2Cl + 2H2O.
(3) MnCl2 + H2SO4 = MnSO4 + 2HCl.
Combining these equations, the following equation expressing the complete reaction is obtained:
2NaCl + MnO2 + 2H2SO4 = MnSO4 + Na2SO4 + 2H2O + 2Cl.
Since the hydrochloric acid liberated in the third equation is free to act upon manganese dioxide, it will be seen that all of the chlorine originally present in the sodium chloride is set free.