A 3-13 A method has been reported (45) for the spectrophotometric determination of chlorate impurity in ammonium perchlorate, NH.CIO, for use in rocketry. This is based on the reduction of chlorate to free chlorine: CIQ +5Cl + 6H3Cl + 3H.O. The chlorine then reacts with benzidine (I) to give a colored product (II) with a maximum absorption at 438 nm. HN- (I) -NH + Cl HN: )=NH 2+ +2C1- (II) Experiments with standard KCIO: solutions showed the following straight-line relation to hold under prescribed experimental conditions (in 10.0-mm cuvets): A = (1.17 X 10) C 0.186 where C is the formal concentration of KCIO. (a) Explain why (II) gives a colored solution while (I) does not. (b) What color is the solution of (II), and what color filter would be suitable for its determination? (c) Does this system obey Beer's law? (d) The term "-0.186" was ascribed to a reducing impurity in the reagents. Explain why this would be expected to give a subtractive term. (e) A sample of 6.000 g of commercial NH.CIO, was suitably treated with reagent and diluted- to 100.0 ml. A portion of this showed an absorbance of 0.450 in a 10.0-mm. cuvet at 438 nm. Calculate the concentration of NH,CIO, in the NH.CIO, in terms of mole percent.