Potentiometric and conductometric studies on the formation of thorium molybdates as a function of pH

Abstract

A formação de molibdatos de tório obtidos pela interação de nitrato de tório com molibdato de sódio a níveis específicos de pH 7,8; 5,5 e 4,1 foi estudada por técnicas eletrométricas envolvendo titulações condutométricas e pH-métricas. As inflexões e degraus bem definidos nas curvas de titulações fornecem evidências incontestáveis sobre a formação de molibdatos normal-ThO 2 .2MoO 3 e para-3ThO 2 .14MoO 3 de tório nas vizinhanças dos pH's 5,3 e 4,4, respectivamente. As investigações analíticas sobre os precipitados de molibdatos de tório também foram realizadas, as quais confirmaram os resultados eletrométricos. The formation of thorium molybdates obtained by interaction of thorium nitrate and sodium molybdate at specific pH levels 7.8, 5.5 and 4.1 have been studied by electrometric techniques involving pH and conductometric titrations. The well-defined inflections and breaks in titration curves provide cogent evidence for the formation of thorium normal-ThO 2 .2MoO 3 and para-3ThO 2 .14MoO 3 molybdates in the vicinity of pH 5.3 and 4.4, respectively. Analytical investigations on the precipitates of thorium molybdates have also been carried out, which support the electrometric results.

Electroanalytical investigations on formation of thallium(I) molybdates as a function of pH

“…The titration curves of both the techniques show two inflections at 7Mo:8H and 8Mo:12H corresponding to the formation of the polyanions para-Mo 7 O 24 6and octa-Mo 8 O 26 4-, respectively (see Figure 1, points A, B and A', B'). The results are similar to those obtained for the interaction of hydrochloric acid with sodium molybdate 17 and are also in conformity with the results of the temperature-jump studies by Honing and Kustin 19 and the Raman spectra studies by Ozeki et al 20 The stepwise condensation of MoO (Figure 2, curve 1), when Na 2 MoO 4 solution was used as titrate, a gradual decrease in pH value was observed till at the stoichiometric end-point (the stage at which the reaction ends if simple double decomposition takes place) a sharp fall in pH was observed (see point A in Figure 2) when the molar ratio of Tl + :MoO 4 2is 2:1 corresponding to the formation of thallium normal-molybdate, Tl 2 O.MoO 3 , in the neighborhood of pH 6.8. In case of inverse titrations (Figure 2, curve 3), the pH at first gradually increases till in the vicinity of stoichiometric end-point when the last traces of thallium ions have been removed by precipitation, further addition of alkali molybdate causes a marked upward jump in pH and the inflection corresponds to the molar ratio for the formation of Tl 2 O.MoO 3 according to the reaction:…”

“…[10][11][12] On account of the complexity of the relation of equilibrium between the polyanions or due to the experimental difficulty in early works, the conclusions of earlier workers seem to be overstrained and hence it was considered worthwhile to make a careful and precise study on the formation of molybdates as a function of pH by electrometric techniques, which have provided more conclusive evidence on the condensation process of vanadate, 13 antimonite 14 thiotungstate 15 and tungstate anions. 16 In an earlier publication 17 Prasad and Gonçalves have reported the effect of pH change on composition of thorium molybdate. The results on formation of thallium molybdates as a function of pH are presented here.…”

Electrometric investigations on formation of lanthanum molybdates as a function of Ph

“…18 The pH and conductometric measurements were carried out in the usual manner. 17 Using different concentrations of the reactants, a series of potentiometric and conductometric titrations was carried out between acid (HCl, HNO 3 ) and sodium molybdate solutions. All observations were made at the state of chemical equilibrium.…”

“…[10][11][12] On account of the complexity of the relation of equilibria between the polyanions or due to the experimental difficulty in early works, the conclusions of earlier workers seem to be overstrained and hence it was considered worthwhile to make a careful and precise study of formation of molybdates in function of pH by electrometric techniques, which have provided more conclusive evidence on the condensation process of vanadate, 13 antimonite, 14 thiotungstate 15 and tungstate anions. 16 In an earlier publication Prasad and Gonçalves 17 have reported the effect of pH change on composition of thorium molybdate. The results on formation of lanthanum molybdates as a function of pH are presented here.…”