Initial Rate Determination of the Crystal Violet – Hydroxyl Ion Reaction

The customary colorimetric initial rate procedure for determining kinetic reactant orders involves a significant determinate error arising from the system setup time delay before the first absorbance value is recorded after an earlier combination of the reactant solutions initiates the reaction. Exemplified in the reaction between crystal violet and hydroxyl ion, a modified colorimetric experimental procedure that virtually eliminates this error source is described in which absorbance measurement is initiated from the moment that the reactant solutions are combined. A data interpolation procedure is then applied to the absorbance versus reaction time relationship to fill in the interval between the known initial value of the absorbance of the test solution at the reaction start and the first value recorded by the colorimeter following the system setup delay. To investigate the effectiveness of this interpolation step in reducing experimental error, the colorimetric procedure is repeated in a colorimetric test system modified to operate in a flowthrough mode to deliver absorbance values from close to the moment at which the reactant solutions are combined.