Question

why we use lambda max to generally monitor reaction, can a wavelength other than lambda be used for alkaline hydrolysis of Crystal Violet experiment , why ?

Answer 1

Generally, at lower wavelengths lots of impurities (including solvents) will absorb, however, they won't be detected at higher wavelengths. The best approach to monitor a reaction uses the lambda max compound as a function of time/another reagent. Also, the analysis at lambda max wavelength determines quantity and purity of our compound. Because lambda max represents HOMO to LUMO transition, any change to the molecule will change the position of HOMO and Lumo and it is advised to monitor the lambda max during a reaction.

Crystal violet shows a lambda max around 600 nm. It is the most appropriate wavelength to monitor hydrolysis. Even though it shows significant absorption below 300 nm, it is difficult to determine by monitoring at these wavelengths. After reaction also, most of the absorption at this region exists.