Potentiometric Titration of Selenic and Telluric Acids with Titanium(III) Chloride in Nonaqueous Solven ts

Abstract

Selenic and Telluric acids were titrated potentiometrically with titanium(III) chloride solution by using Pt-Cu⋅Hg bimetallic electrodes in nonaqueous solvents such as N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), isopropyl alcohol (IPA) and the mixtures of these solvents.
It was found that selenic and telluric acids were titrated directly at room temperature in DMF solution without hydrochloric acid. The molar ratios of selenic and telluric acids to titanium (III) chloride was 1: 6. However, the corresponding reactions to SeO₄^2-→SeO₃^2- or TeO₄^2-→TeO₃^2- were not confirmed in the titration curve in DMF.
In the titration of selenic acid in mixed solvents of DMF and IPA in 1: 1 or 1: 2 ratio, two steps were observed. The first and the second steps were appeared on the titration curve at molar ratios of 1: 2 and 1: 6, respectively.
It was interpreted that the first step c orresponded to the intermediate reaction of SeO₄^2-→SeO₃^2-
Mixed solution of selenic and telluric acids were determined by the proposed method. Three steps were observed on the titration curve. It was interpreted that the first, second and third steps corresponded to the reaction of SeO₄^2-→SeO₃^2-, SeO₃^2-→SeO₃^2-Se(0), and TeO₄^2-→Te(0), respectively. Less than 5% of water gave no influence on the titration.