Both the iron(III) chloride and the nickel(II) nitrate have in color of their own.
This that they both absorb wavelengths of light in the visible region of the spectrum. we can use the visible spectrophotometer to investigate the pattern of absorption of light in the visible region,to obtain the visible transmittance or absorption spectra of the solutions. By comparing the pattern of absorption spectra of the pure substance contaminant that absorbs more of a particular wavelength (or range of wavelength) than the pure material then the shapes of these curves will be changed. The change could show up in the form of a bump that wasn’t there for the pure material, ora change in a wider range of wavelengths to higher or lower levels. If the entire curve of the suspect.It is likely due to a concentration difference and not a contaminant.In that case, the color of the material and their solutions may still be visibly different but it will not show up in the spectra. Do not forget to mention about this possibility in your conclusion if your results show that there is not any contaminant.