pH change of thiourea solution in the reaction with iodine-azide.

Iodine-azide reaction and its application to quantitative micro-analysis. VIII.

Abstract

When iodine-azide was added to the insufficiently buffered thiourea solution, the pH was lowered showing a distinct shift. The cause of this phenomenon was persued and the results indicated that this was not due to the absorption of carbon dioxide by the solution nor to the dilution by the additional solution, but to the chemical reaction itself between thiourea and iodine-azide. The more extensive studies led to the conclusion that the pH lowering was attributable to iodine, not to sodium azide in the reagent.
The studies were furthermore extended, where by several kinds of thiourea solutions, in which thiourea concentration and pH were the same but the sorts and amounts of buffering agents contained were different each others, were prepared and variations of pH of these solutions with the addition of iodine-azide or the related solutions were estimated.
The results were summarized in several graphs, which indicated that even though the pH of thiourea solutions were all the same before the titration, the pH change during or after the titration were not always same, depending on how the pH of thiourea solution was initially adjusted. Accordingly, the notice must be taken of this point, if this method would be about to be applied for analysis of thiourea under the fixed condition of pH.