Why Does Crystal Violet Show Different Reaction Orders at Different Wavelengths?

[Soaring Crane]

In the reaction of CV with NaOH, the order of CV is 1 (first order). However, in an experiment that I did with a colorimeter, I did not entirely come up with this value. Graphical analysis was done to determine the best wavelength from the absorption spectrum and lambda_max = 590 nm.
After looking at the absorbance readings (or manipulations of A in relation to each order) vs. time at 0 order through 2nd order at 590 nm, it was concluded that 0 order (A vs t) gave the best line; this does not match the true value.

On the other hand, at 526 nm, which had a lower absorbance level than 590 nm, absorbance readings (and its manifestations) vs. time had the best line at first order (ln A vs t) than 0 and 2nd orders. Exactly why is the true value (first order) available at 526 nm but not at the lambda_max 590 nm?

 

[GCT]

In general, for quantitative analysis, it's better to pick a broad and smooth region for the absorbance and one between .5-1 abs units, at higher abs several things contribute to deviancy from beer's law. What was the respective absorbance values for the two wavelengths, what did the graphs look like? It may be that if you had analyzed the spectrum at a wavelength peak with high absorbance, such as due to inadequate dilution, the trend in the dynamic range may not be dependable. What instrument are you using?

 

[Soaring Crane]

Actually, I just found out that the CV preparation was not that great.