Cerous sulphate, Ce₂(SO₄)₃

In 100 parts of ice-cold water 40 parts of cerous sulphate can be dissolved. The specific heat (0°to 100°) of the anhydrous sulphate is 0.1168.

Cerous sulphate forms numerous hydrates. The existence of hydrates with 4H₂O, 5H₂O, 8H₂O, 9H₂O, and 12H₂O is definitely established, but the existence of the hydrate with 6H₂O is very doubtful.

Solubility of the hydrates of cerous sulphate in water

The various hydrates may be obtained as follows: - The dodecahydrate, Ce₂(SO₄)₃.12H₂O, separates from a concentrated solution of cerous sulphate over sulphuric acid at 0°C. in the form of tiny needles. The enneahydrate, Ce₂(SO₄)₃.9H₂O, is prepared by evaporating the aqueous solution at 40°-45°, and forms hexagonal prisms. The octahydrate, Ce₂(SO₄)₃.8H₂O, is best prepared by warming to 45°-50° a solution of the sulphate that was saturated at 0° C. The pentahydrate, Ce₂(SO₄)₃.5H₂O, is obtained by preparing a cold saturated solution and heating it to 70°-100°, and forms monoclinic prisms. The tetrahydrate, Ce₃(SO₄)₃.4H₂O, is conveniently prepared by agitating the enneahydrate with a little water at 70° for 48 hours, and drying the mass at the same temperature.

The octahydrate has been generally regarded as crystallising in the orthorhombic system; but according to Wyrouboff, whose view is adopted by Groth, the crystals are triclinic and devoid of all elements of symmetry (a:b:c = 1.0650:1:1.1144, α = 90°52', β = 90°40', γ = 91°45'). Kammelsberg has described a monoclinic octahydrate, isomorphous with the octahydrates of the other metals.

The solubilities of the various hydrates, in grams of anhydrous sulphate per 100 grams of water, are given in the accompanying table (Koppel) and represented graphically in fig., from which the stable hydrate at any temperature is readily seen. It will be noticed that solubilities have been determined even where the hydrates are metastable in contact with the solution.

The acid sulphate, Ce(HSO₄)₃, is known.

The following double salts with alkali sulphates have been described: - Ce₂(SO₄)₃.K₂SO₄.2H₂O; 2Ce₂(SO₄)₃.3K₂SO₄, and with 8H₂O; Ce₂(SO₄)₃.2K₂SO₄.2H₂O; Ce₂(SO₄)₃.3K₂SO₄; Ce₂(SO₄)₃.5K₂SO₄. Ce₂(SO₄)₃.Na₂SO₄.2H₂O; Ce₂(SO₄)₃.(NH₄)₂SO₄.8H₂O, and anhydrous; Ce₂(SO₄)₃.5(NH₄)₂SO₄.

They are sparingly soluble in water and practically insoluble in saturated solutions of the corresponding alkali sulphates.

The diminution in the solubility of cerous sulphate in water, caused by the presence of various alkali sulphates, is as follows (data represent grams of anhydrous salt present in solution per 100 grams of water): -

Temp. 16° C.		Temp. 19° C.		Temp. 16° C.
K2SO4.	Ce2(SO4)3.	Na2SO4.	Ce2(SO4)3.	(NH4)2SO4.	Ce2(SO4)3.
0.00	10.75	0.00	9.65	0.00	10 75
0.18	0.96	0.33	0.64	3.46	1.03
0.51	0.43	1.09	0.09	9.32	0.78
0.73	0.25	1.39	0.06	19.24	0.75
1.29	0.04	1.70	0.03	45.62	0.50
2.50	0.00	3.59	0.01	72.84	0.04

Cerous ammonium sulphate, Ce₂(SO₄)₃.(NH₄)₂SO₄.8H₂O, is a monoclinic salt of density 2.523. It loses 6H₂O at 100°, and the remaining 2H₂O at 150°. The solubility, in grams of Ce₂(SO₄)₃.(NH₄)₂SO₄ per 100 grams of water, is as follows (Wolff): -

Temp. °C	22.3°	35.1°	45.2°
Grains of Ce2(SO4)3.(NH4)2SO4	5.33	5.18	4.99

Above 45° the anhydrous double salt is the stable phase in contact with the solution, and its solubility is as follows (Wolff): -

Temp. °C	45°	55.3°	75.4°	82.2°
Grams of Ce2(SO4)3.(NH4)2SO4.	2.99	2.24	1.48	1.18

The sulphates of hydrazine and hydroxylamine combine with cerous sulphate.

Cerous thallous sulphate, Ce₂(SO₄)₃.Tl₂SO₄.4H₂O, crystallises in monoclinic prisms (a:b:c = 1.1309:1:0.7059, β = 91°53'). The salt Ce₂(SO₄)₃.3Tl₂SO₄. H₂O has also been described.

Cerous cadmium sulphate, Ce₂(SO₄)₃.CdSO₄.6H₂O, crystallises in the orthorhombic system (a:b:c = 1.1336:1:0.7535).

Cerous nitratosulphate, Ce(NO₃)(SO₄).H₂O, crystallises out when a solution of cerous sulphate in concentrated nitric acid is evaporated on the steam-bath.