Light, Color and Solutions

Light, Color and Solutions

Effects of Concentration and Cell Path Length on a Solutions Absorbance
To examine the relationship between color of a solution and the light it absorbs. When it comes down to it our eyes do a accurate job of depicting and distinguishing colors. The purpose of this experiment is to take that a little farther, become more precise. With the use of a spectrophotometer one can determine the wavelength and intensity of the light absorbed. By adding a light source to the solution we can determine the spectrum of that solution, or in other terms the light absorbed. Absorbance is a key part of the experiment, especially the relationship between absorbance and concentration. In other terms, the higher the absorbance, the deeper the color; also the more light absorbed, the less light that passes through.

Now when it comes to combining colors, there’s a discrepancy between the color light spectrum, and the painters color spectrum. Since being a child you know that combining two colors would give you one solid color. The same falls true in chemistry, when you combine two chemicals you’ll get the respected outcome, for example, blue and red will make purple. Now in the experiment when you add Erioglaucine and Allura Red, the color emitted is the same as it would be with Crystal Violet. In reality they’re both purple, but when you take closer look at it the color spectrum for Crystal Violet is different then that of the combination to make purple. When you look at the combination of Allura Red and Erioglaucine you see a combination of the red and blue color spectrum. So as far as the color wheel goes, to the eye they’re the same, but when you mix light, you combine the color spectrums, creating a different one than as if it was just the primary color. Beer’s Law shows the relationship for absorbance of a material in which light is passing: A=ebc ( A being absorbance, e being molar absorptivity , b being path of the length of the sample, and c being the concentration of the sample)

The uses of Beer’s law can help determine the identity of an unknown solution, simply by using the spectrometer and the aforementioned formula by using a linear graph seeing the relationships between concentration and absorbance, along with molar absorptivity and cell path length. All of which can be used to solve the other. In real world cases Beer’s Law is used to make sports drinks nowadays such as Powerade and Gatorade. Yet there are limitations to Beer’s Law, in reality Beer’s Law would fall under ideal circumstances, its limited by the fact that the equilibrium concentration of the solution could be differentiated between samples or stray light does get involved.

References
Brown, Theodore; Chemistry: The Central Science, Prentice Hall: Upper Saddle River, New Jersey, 2012

Dartmouth College, Chem Lab: Color and Light, , (accessed 11-08-12)

Potts, Gretchen E. Beers Law, http://www.utc.edu/Faculty/Gretchen-Potts/chemistryhelp/beers.htm, ( accessed 11-08-12)