ABSTRACT
Objective To identify the tones of yellow color of chlorinated water sample reacting with color reagent containing 3,3' ,5,5' -tetramethylbenzidine with the color of standard colorimetric series in process of determination of free chlorine in drinking water by colorimetry method. Methods The dispensation and the adding amount of color reagent into water sample were adjusted to select the optimum experimental conditions. Results The water sample reacting with color reagent showed expected yellow color at the concentration of HC1 in color reagent e" 0.5 mol/L. Conclusion The reaction of 50 ml water sample (0.1-0.5 mg/L free chlorine) with 1.00 ml color reagent at concentration of 0.3 g/L prepared by 0.50 mol/L HC1 revealed the same tone of yellow color as that on the standard colorimetric series in optical colorimetry method.