Triphenylmethane dyes as oxidation-reduction indicators in titrations with cerium (IV) perchlorate

Abstract

1. It has been shown that erioglaucine A, eriogreen B and xylene cyanol FF function excellently as internal indicators in the titration of iron(II), uranium(IV), oxalic acid and hydroquinone by ceric ammonium nitrate in 0.5–4 N perchloric acid medium. The titrations can be done with the normal speed, the dyes indicating the equivalence point sharply and accurately. The indicator reactions involved in the titrations have been found to be reversible. 0.5 ml of a 0.1% aqueous solution of the dye is sufficient for 50–100 ml of the titration mixture. The dye which has an yellow colour in acid solution turns to an orange red sharply on the addition of a slight excess of the cerium(IV) salt solution. The indicator correction is practically negligible with 0.1 N or 0.05 N solutions of the cerium salt. The indicator correction amounts to 0.1 ml of 0.01 N cerium(IV) salt solution. These dyes do not function satisfactorily in the titration of vanadium(IV) and molybdenum(V) with ceric ammonium nitrate in perchloric acid medium. 2. The use of triphenyl methane dyes as redox indicators in titrations with cerium(IV) perchlorate is a great convenience, because the other two indicators available for the purpose, nitroferroin and rutheniumdipyridyl, are costly.