Most Hazardous Materials
The dyes used in this experiment are FD&C Blue #1 and FD&C Red #3 dyes, which have been approved for use in food and are non toxic in amounts encountered in this experiment. Pretty much anything is toxic in large enough amounts, but for all practical purposes, these dyes are harmless. They may stain skin or clothing, if spilled, however.
Additional, not required, but fascinating info:
These dyes have complex, extensively conjugated organic structures, (alternating single and double bonds and/or aromatic rings). This type of structure lowers the energy of light required to promote electrons to the next available energy level from the energetic ultraviolet region into the visible region, and results in absorption of visible light. The dyes also have substituents which are acidic or basic in character and thus will have different colors in acid and basic solutions.
This is comparable to the behavior of phenolphthalein, which we used as an indicator for the equivalence point in the standardization of NaOH by titration. The colorless form needs higher energy ultraviolet light to promote electrons to the next available state, so we can’t see this process with our eyes. Using instruments, we could measure this just like in the more easily accessable visible region. The red form of phenolphthalein has a more delocalized structure, lower energy levels and shifts its absorption from the ultraviolet into the blue region. We see the light which is not absorbed as an excess of red light remaining after the molecules have removed the blue from the overall mixture present in ‘white’light.
If you find this sort of thing interesting, see chapters on organic chemistry or look up conjugation, resonance or delocalization in the index of most any freshman text. For a more advanced treatment, see an introductory spectroscopy, introductory organic text or organic lab manual.
The best book in the UMR library that I am aware of for an introductory level, largely non-mathematical treatment of the origins of color is:
TITLE(S): The physics and chemistry of color : the fifteen causes of color / Kurt Nassau, Wiley, New York (1983) Call No.: QC495 .N35 1983
I highly recommend it if you have the time or interest. It also has some excellent color photos to illustrate everyday examples.
Such as, did you know that there is actually no color in butterfly wings? It is an interference effect due to the wing thickness, similar to the colors produced by oil or gasoline films on water or the colors of soap bubbles. Pretty cool, huh?
Web Links of Interest
Info on Beer-Lambert law of light absorption
A Spectroscopy Course/Includes Advanced Level Information
Less Hazardous Materials
The only thing in this experiment less toxic than the dyes, is the water they are dissolved in, which we all know can be fatal in certain circumstances.