Scandium fluoride, ScF₃

Scandium fluoride, ScF₃, is obtained as a white powder, difficult to filter, by heating scandia with aqueous hydrofluoric acid, or by precipitating a solution of a scandium salt with hydrofluoric acid, an alkali fluoride, or fluosilicic acid. The fluoride is fusible with difficulty in the blow-pipe flame. It is very slightly soluble in hydrochloric acid, in which it resembles the thorium salt and differs from the salts of the rare earth metals (Crookes; Meyer and Wassjuchnow).

Scandium fluoride, like zirconium fluoride, is soluble in solutions of the alkali fluorides. Scandium ammonium fluoride, ScF₃.3NH₄F, is readily soluble in water, from which it crystallises in octahedra. It is decomposed by hydrochloric or dilute sulphuric acid with the precipitation of scandium fluoride or scandium ammonium sulphate. In aqueous solution it may be regarded as yielding chiefly the ions 3NH₄' and ScF₆''', since it does not give any precipitate when boiled with ammonia. Sodium or potassium hydroxides, however, precipitate scandium hydroxide. The corresponding potassium and sodium salts, ScF₃.3KF and ScF₃.3NaF, are known; they are less soluble in water and less "complex" than the ammonium salt (Meyer and Wassjuchnow).