Keywords
lanthanum
electrometry
polyanions
How to Cite
Abstract
The stoichiometry of the polyanions formed by the action of nitric acid on sodium tungstate(≤ 0.01M) has been studied by means of electrometric techniques involving pH-potentiometric and
conductometric titrations. The well defined inflections and breaks in the titration curves provide
evidence for the existence of the polyanions, para-W 12 O 4110- and meta-W 12 O 396- corresponding to the
ratio of H + :WO 42- as 7:6 and 9:6 in the pH ranges 5.7-6.0 and 3.6-4.1, respectively. The interaction of
lanthanum nitrate with sodium tungstate solutions, at specific pH levels 8.0, 5.9 and 4.0 was also
studied by pH and conductometric titrations, in aqueous and alcoholic media, with each of the reagents
alternatively used as titrant. The electrometric experiments provide definite evidence of the formation
of normal-La 2 O 3 .3WO 3 , para-5La 2 O 3 .36WO 3 and meta-La 2 O 3 .12WO 3 tungstates in the vicinity of pH
6.3, 5.0 and 4.2, respectively. Analytical investigations on the precipitates formed confirm the results
of the electrometric study.
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