Photometric Determination of Trace Amount of Chromium(Ⅵ) Based on Its Catalytic Effect on Decolorization of Methyl Orange

In a 0.05 mol·L-1 H2SO4 medium,the oxidative color-fading reaction of methyl orange with hydrogen peroxide was remarkably catalyzed by the presence of trace amount of Cr(Ⅵ),when heated in a water bath at 90 ℃ for 9 min.Under the optimum condition,linear relationship between the values of decrease in absorbance (ΔA) and concentration of Cr(Ⅵ) was obtained in the range within 72 μg·L-1.The apparent activation energy of the above mentioned catalytic reaction was found to be 25.73 kJ·mol-1.Detection limit (3s/k) of the reaction found was 0.058 mg·L-1.Based on these facts,a photometric method for determination of trace amount of Cr(Ⅵ) in industrial waste water and lake water was proposed.In analyzing 3 water samples by this method,results of Cr(Ⅵ) found were in consistency with the results found by the DPC photometric method.