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 and the off-colored samples.
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, or
a change in a wider range of wavelengths to higher or lower levels. If the entire curve of the suspect
sample is raised or lowered (rather than its shape changed), it is likely due to a concentration
difference and not a contaminant. Another addition point is that it is possible for a contaminant to not
have a color or to not absorb in the visible region of the spectrum. 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.