REACTIONS OF SOME LESS COMMON IONS

In the previous chapters the discussions were restricted to those cations and anions which occur most often in ordinary samples. Having studied the reactions, separation, and identification of those ions, the reader should now concentrate on the so-called rarer elements. Many of these, like tungsten, molybdenum, titanium, vanadium, and beryllium, have important industrial applications. 

No attempt has been made to give more than a short introduction to the subject to economize on space, most of the simple equations have been omitted. The elements have been classified, in so far as is possible, in the simple groups with which the reader is already familiar, and methods of separation have been briefly indicated. Thus thallium and tungsten are in Group I molybdenum, gold, platinum, selenium, tellurium, and vanadium in Group II and beryllium, titanium, uranium, thorium, and cerium in Group III. It is hoped that the subject-matter of this chapter will suffice to enable the reader to detect the presence of one or two of the less common ions. 

Thallium is a heavy metal with characteristics reminiscent of lead. It melts at 302.3 C. Thallium metal can be dissolved readily in nitric acid it is insoluble in hydrochloric acid. 

Thallium forms the monovalent thallium(I) and trivalent thallium(III) ions, the former being of greater analytical importance. Thallium(III) ions are less frequently encountered in solutions, as they tend to hydrolyse in aqueous media, forming thallium(III) hydroxide precipitate. Thallium(I) ions can be oxidized to thallium(III) ions in acid media with permanganate and hexacyanoferrate(III) ions as well as with lead dioxide, chlorine gas, bromine water or aqua regia (but not with concentrated nitric acid). The reduction of thallium(III) ions to thallium(I) is easily effected by tin(II) chloride, sulphurous acid, iron(II) ions, hydroxylamine or ascorbic acid. 

TI+ reactions Reactions of thallium(I) ions To study these reactions a 0.025m solution of thallium(I) sulphate, TI2SO4, or a 0.05m solution of thallium(I) nitrate, TINO3, should be used. All these compounds are HIGHLY POISONOUS. 

The term rarer elements as originally employed in the sense of their comparative rare occurrence and limited availability must now, in a number of cases, be regarded as a misnomer. Large quantities of some of these elements are utilized annually, and the range of their application is slowly but surely widening. A few examples may be mentioned the use of molybdenum, tungsten, titanium, and beryllium in the steel industry, of tungsten in the manufacture of incandescent lamps, and of titanium and uranium in the paint industry. The interpretation of the term rarer elements, as applied to the elements described in this chapter, is perhaps best accepted in the sense of their comparatively rare occurrence in routine qualitative analysis. 

Thallium forms the monovalent thallium and trivalent thallium(III) ions, the former being of greater analytical importance. Thallium(III) ions are less frequently encountered in solutions, as they tend to hydrolyse in aqueous solution, forming thallium(III) hydroxide precipitate. Thallium ions can be 

---