Ceric sulphate, Ce(SO₄)₂

Ceria is quantitatively converted into ceric sulphate when heated on a sand-bath with concentrated sulphuric acid. The salt, which is insoluble in the excess of acid, may be washed with glacial acetic acid and dried over potash, when it is obtained as a deep yellow, crystalline powder. When heated in the air, slight loss of weight is observed at 155°, and when heated to constant weight at 195° the basic sulphate 3CeO₂.4SO₃ is produced. On raising the temperature, further loss of sulphur trioxide occurs at 250°, and at 300° the loss in weight is continuous until cerium dioxide is left.

Ceric sulphate is very soluble in water, in which it forms a yellowish-brown, unstable solution. A concentrated solution of the salt in dilute sulphuric acid may be prepared either by dissolving the anhydrous salt in dilute sulphuric acid or by carefully dissolving ceric hydroxide in the same medium. When concentrated over sulphuric acid, sulphur-yellow, orthorhombic crystals of the tetrahydrate, Ce(SO₄)₂.4H₂O, are obtained (bipyramidal; a:b:c = 0.717:1:0.471).

Ceric sulphate in solution readily hydrolyses, and, according to Wyrouboff and Verneuil, when diluted largely or warmed, a crystalline basic salt of the composition 2CeO₂.2SO₃.5H₂O is obtained; from a dilute ice-cold solution the compound 4CeO₂.3SO₃.12H₂O has been prepared, and from a saturated solution at 0° C. the compound 2CeO₂.3SO₃.4H₂O. A physicochemical study of the hydrolysis has been made by Spencer, who could only prepare and characterise one basic salt at 25° C., viz. CeO₂.SO₃.2H₂O.

Ceric potassium sulphate, Ce(SO₄)₂.2K₂SO₄.2H₂O, is obtained in orange-yellow, monoclinic crystals (a:b:c = 1.216:1:2.093; β = 100°40'), scarcely soluble in water, by adding a solution of potassium sulphate to an acid solution of ceric sulphate.

Ceric ammonium sulphate, Ce(SO₄)₂.2(NH₄)₂SO₄.2H₂O, separates in yellow crystals when an acid solution of the mixed sulphates is evaporated: it is followed by orange-red crystals of the monoclinic (a:b:c = 0.6638:1:0.7838; β = 96°44') double salt Ce(SO₄)₂.3(NH₄)₂SO₄.2H₂O.

Ceric silver sulphate, 5Ce(SO₄)₂.3Ag₂SO₄, is obtained as an orange-yellow, crystalline precipitate by adding silver nitrate to a strongly acid solution of ceric sulphate. The salt slowly combines with 2H₂O, and is decomposed by boiling water.