Sulphates are inorganic salts containing sulphate ion. Sulphate ion is a plyatomic anion in which the central sulphur atom is surrounded by four equivalent oxygen atoms in a tetrahedral arrangement. In sulphate ion, the sulphur atom is in the +6 oxidation state while the four oxygen atoms are each in the -2 states. Sulphate ion forms many salts like sodium sulphate, potassium sulphate, barium sulphate etc. The very well known coloured salts of sulphate are green vitriol and blue vitriol.
This video explains how to test the presence of sulphate ion in a given salt.