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A physico-chemical study of the conditions of formation (pH, time, temperature) of dodecatungstates and of their separation with tetraphenylphosphonium chloride is presented. In the iso- and heteropolytungstate series only the anions of the form [XW(12)O(40)]((8-n)-(where n is the oxidation number of X) are precipitated by this reagent. The reaction is quantitative and can be used to separate the dodecatungstate from a mixture of tungstate anions. By using tetraphenylphosphonium chloride as a specific reagent for dodecatungstate it has been possible to show that in the condensation of sodium tungstate in high concentrations of acid the dodecatungstate begins to appear at pH ~ 6 and all the tungstate is in this form at pH ~ 2. Factors such as dilution, time and temperature also affect the formation of dodecatungstate over this pH range. The reaction is used for the determination of a series of dodecatungstates.
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Institut de chimie de l'Académie de la République Socialiste RoumaineFrance.
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