We have given some direction from Dr. Otto Speck and Professor Will B. Green for the investigation as
follows;
Both the iron(III) chloride and the nickel(II) nitrate have color of their own. Their solutions also have
a color of their own. This indicates that they both absorb wavelengths of light in the visible region of
the spectrum. Since we do not need to identify the contaminants, we can use the visible
spectrophotometer to investigate the pattern of absorption of light in the visible region, i.e., 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, we can identity if the samples
are in fact out-of-spec or not.
All you need to do is to prepare solutions of all samples, then get the pattern of absorption spectra
from the UV-VIS Spectrophotometer. Compare the pattern between the pure and suspect samples,
you will then know if there is any contaminant.
Something to keep in mind is that if there is a 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.