Analysis of Tin Plating Solutions by Using EDTA

Abstract

Sn^II in the plating solutions can usually be titrated by iodin method. Sn^IV therefore, must be reduced to Sn^II for the titration. This reduction, however, is rather difficult and might cause some error due to the oxidation by air during the course of analysis.
So, the author tried to develop a method to avoid such an error as follows:
First, Sn^II was titrated directly in the EDTA standard solution, masking Sn^IV with NH₄F, keeping pH at 5.5-6.0, with pyridine-acetic acid as buffer solution and using methyltymol blue as indicator.
Next, to analyse Sn^II+Sn^IV, another portion of the solution was made acidic with HCl., to which an excess amount of EDTA standard solution was added and boild for a few minutes. Keeping the pH value of the solution between 2.5 and 3.5 with CH₃COONH₄ using dinitrophenol as pH indicator, it was then back titrated with Th^IV standard solution with xylenol orange as indicator.
Figures obtained by this process descrived above were coincident with those given by iodin method for Sn^II and by gravity method for Sn^IV+Sn^II.