Abstract
In the work on vanadates described in this thesis, an attempt was made to identify all stable ions in their solutions from the alkaline side of neutrality, at pH 10, to the lowest pH value that vanadic acid attains, pH 2. From a study of the reactions of vanadate solutions with anion exchangers of varying porosity, it was shown possible, by means of an ionic sieve mechanism, to separate ions of differing degrees of complexity physically in much the same way as that achieved by early workers using diffusion and dialysis. However, it was possible in the present work to identify them chemically. Despite the obstacles to the investigation of the isopoly acids, namely the chemical similarity between the different isopoly anions and the fact that condensation phenomena are continuous with the possibility that the products of two or more stages of condensation can exist side by side, this ion exchange technique could give valuable information because it imposed discontinuities on a system showing otherwise a continuous variation in properties. It has been possible to show the existence of five stable ions in these solutions from the most complex, apparently a decavanadate, at pH 2, to the pyrovanadate, a divanadate, at about pH 10. The results obtained in the present study would indicate that the ionic sieve properties of ion exchange resins may be of value in the study of other isopoly and heteropoly acids. The work on quinquivalent vanadium phosphates, which consisted of a study of the phase diagram of the system V[2]O[5]-P[2]O[5]-H[2]O, indicated that two stable compounds of the yellow or luteo type are formed in acid media. These are V[2]O[5].P[2]O[5].6H[2]O and V[2]O[5].1.5P[2]O[5].5H[2]O that is (VO)PO[4].[6]H[2]O and (VO)[2](HPO[4])[3].7H[2]O. Investigations of phosphovanadate solutions indicated the presence of the ion 5V[2]O[5].O.5P[2]O[5].2.5H[2]O.nH[2]O, that is H[5]V[10]O[26].PO[4].nH[2]O. It would further appear that this is possibly the only phosphovanadate ion to be formed in solution.