Electrometric studies on the system acid-vanadate and the formation of heavy metal vanadates

The stoichiometry of the polyanions formed by the action of nitric acid on sodium ortho-vanadate solution has been studied by means of electrometric t echniques involving glass electrode and conductometric titrations as well a s Job's method of continuous variation. The well defined inflections and br eaks in the titration curves and maxima from continuous variation study pro vide cogent evidence for the existence of the anions, pyro-V2O74-, meta-VO3 - and poly-H2V10O284- corresponding to the ratios of VO43-:H+ as 1:1, 1:2 a nd 1:2.6 in the pH ranges (10.1-10.7), (7.0-7.5) and (3.4-3.8), respectivel y. Similar titrations between alkali and V2O5 solutions also confirm the ex istence of the same anions,The interaction of lead nitrate with sodium vana date solutions, at specific pH levels 12.4, 10.5, 7.4 and 3.6 was also stud ied by pH and conductometric titrations. The end-points obtained from the s harp inflections in the titration curves provide definite evidence for the formation of lead ortho-3PbO . V2O5, pyro-2PbO . V2O5 and meta-PbO . V2O5 v anadates in the vicinity of pH 8.2, 6.5 and 5.6, respectively. (C)2000 Else vier Science B.V. All rights reserved.