A yellow hygroscopic compound, Fe2(SO4)3; rhombic; r.d. 3.097; decomposes above 480°C. It is obtained by heating an aqueous acidified solution of iron(II) sulphate with hydrogen peroxide:2FeSO4+H2SO4+H2O2 → Fe2(SO4)3+2H2O On crystallizing, the hydrate Fe2(SO4)3.9H2O is formed. The acid sulphate Fe2(SO4)3.H2SO4.8H2O is deposited from solutions containing a sufficient excess of sulphuric acid.
2FeSO4+H2SO4+H2O2 → Fe2(SO4)3+2H2O