pH滴定法による強リン酸の組成分析

概要

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A simple method for the composition analysis of strong phosphoric acid involving ortho-, pyro-, tripoly- and tetrapoly-phosphoric acid has been given. The diluted sample solution was titrated with an alkali using an automatic titrometer with recorder. Calcium chloride solution was added at a position just beyond the second inflection point of the titration curve and the titration was continued to the third inflection point. The moles of base required from the beginning to the first, from the first to the second and from the second to the third inflection point of titration curve are equivalent, respectively, to the content of strongly acidic hydrogen ion or total phosphorus atom, weakly acidic hydrogen ion except the third hydrogen of orthophosphoric acid and the third hydrogen ion of orthophosphoric acid. On the other hand an aliquot of the sample solution was brought to pH 3.83.9, and pyrophosphoric acid was determined after precipitation as zinc salt. The strong phosphoric acid prepared by heating 85% orthophosphoric acid were analyzed by this method and reasonable results were obtained.
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