First-order Decomposition of the Violet Colored Ce(lV) Oxidation Product .of ~PhenylanthranilicAcid Standardization of Ce(IV) by Fe(I1) with nphenylanthranilic acid as indicator is well known ( I ) . .* The end point of this titration is marked by the appearance of violet color of the oxidized form of the in,, dicstor. It has been observed that the color of the so'' lution slowly changes from violet t o yellow after the end point. The fading of the violet color (which could ., be regarded as decomposition of the oxidized form of "' the indicator) measured on a colorimeter forms a good exercise for undergraduate students studying T."., ,.~~"*, .,-.,,.~**. chemical kinetics. The decomposition is simple first- ~i~~~~ Figure 2. Plot of log (dl) versus 1. plot of optical density order. unrclnl titime. Cerie sulfate solution was prepared in 1 M H2S01 and standardized against F d I I ) using nphenylanthranalic acid as indicator. The indicator solution was prepared by dissolving 0.1 g of it in 5 ml of 0.1 N NaOH and diluting to 50 ml with water. Ce(1V) and the indicator solutions were mixed so as t o yield a reaction mixture containing 1 X M CdIV) and 1 X 10-' M n-phenylanthranilie acid (NPA) and 1.0 M H&Oa at 25°C. Optical densities of tnis mixture were measured st intervals of :i0 sec at 5811nrn on n Spertronlr 20. ('e I\') and NP4 do n
