Chemical Properties of Scandium

Scandium salts derived from colourless acids are themselves colourless and devoid of absorption spectra. They are diamagnetic, and have a sweet, astringent taste. In aqueous solution they are perceptibly hydrolysed. This will be seen from the following values for the equivalent conductivities of scandium chloride and other chlorides, the abnormal increase in the conductivity of scandium chloride with dilution from v = 32 to i; = 1024 litres being due to the high ionic mobility of the hydrogen ions of the acid set free by hydrolysis: -

Temperature, 25° C.
v =	32	64	128	256	512	1024	λ1024 - λ32
ScCl3	104.7	111.7	119.0	126.2	133.6	142.5	37.8
LaCl3	105.8	112.1	118.0	123.4	127.3	131.5	25.7
CeCl3	107.6	114.4	121.3	126.8	131.1	135.2	27.6
AlCl3	99.9	106.9	114.1	123.8	131.0	138.0	38.1

The basic oxide scandia, Sc₂O₃, from which the scandium salts are derived, is decidedly stronger than alumina. It is, however, weaker than any of the rare earths of the type R₂2O₃.

Scandium is often included among the rare earth elements. In doing so, however, it becomes difficult to decide whether scandia is to be regarded as an earth of the cerium or of the yttrium group. So far as basicity of oxide and solubilities of salts are concerned, scandium resembles the yttrium group; on the other hand, the solubility of its double potassium sulphate places it with the cerium group. It differs from both groups in not forming a sulphate, Sc₂(SO₄)₃.8H₂O, and a nitrate, Sc(NO₃)₃.6H₂O. Further, scandium has a marked tendency to form what are probably complex as distinguished from double salts, and in this and in other respects it shows a remarkable resemblance to thorium. In view of the fact that the cerium and yttrium groups of rare earth elements are distinguished by their platinocyanides, it is of interest to note that scandium platinocyanide, Sc₂[Pt(CN)₄]3, forms hydrates both with 18H₂O and with 21H₂O.

A few salts of scandium were described by Nilson and Cleve; many others have since been prepared and described by Crookes, and by R. J. Meyer and his co-workers.