Light Inquiry Lab formal write-up

Light Inquiry Lab formal write-up - Light Inquiry...

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Light Inquiry, Experiment 9 Determining the Identity of Dyes and Their Concentrations in Kool Aid Amadeia Rector Section 800, Suzanne Ali November 23, 2009 Abstract The purpose of the lab “Light Inquiry” was to utilize the concepts of absorbance and transmittance of light in order to determine the identify of the dyes and their respective concentrations in Grape Kool Aid and Cherry Kool Aid. UV/Vis spectrophotometry was used in order to examine the respective wavelengths where maximum light was absorbed by the various dyes, the Grape Kool Aid, and the Cherry Kool Aid . The dyes identified peaked in absorbance at the same wavelength as the Kool Aid. In this lab, the dyes Red 40 and Blue 1 were identified in Grape Kool Aid, and Red 40 was identified in Cherry Kool Aid. Beer’s Law plots of the four dyes were used to find the ex- tinction coefficients ( ) of each of the dyes, which were then used to determine the con ε - centration of the dyes in the Kool Aid. Using a spectroscope,the transmittance of colors through colored filters were compared in order to determine how the color of Kool Aid might be changed by viewing it under a tinted glass. Filters such as red transmitted primarily blue and red, meaning that the ob- served color of Kool Aid will change depending on what light is transmitted through the filter. Introduction : In the lab “Light Inquiry,” the objective was to determine the concentration and identity of dyes in Kool Aid by use of UV/Vis spectrophotometry and Beer’s Law plots as well as to examine the transmittance of light through colored filters and how observed color changed through these filters. Absorbance of a photon occurs when an electron makes a transition to a higher energy state, meaning that the number of photons is directly correlated to the number of particles in the path of the light beam. The colors seen in an solution or in a light beam are the colors of light transmitted. Whatever colors are not seen are the colors of light that are absorbed. Perceived colors are defined by their wavelengths, which are con- tained in the visible spectra range of 380 nm to 740 nm. A spectrometer is able to measure the absorbance of a solution by calculating the in- tensity (I), the number of photons, of a light beam before and after it passes through a solution via the equation:
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Light Inquiry, Experiment 9 Equation 1: A = log( I t I 0 ) . Whichever wavelength of light is absorbed the most appears as a peak in a graph of Absorbance vs. Wavelength. Likewise, the wavelengths of light that are transmitted are depicted as being low in absorbance. Absorbance depends on the the wavelength of the sample solution ( ), the path length λ the light beam must travel through the sample solution ( ), the extinction coefficient ( ), ι ε and the concentration (c) of the sample solution. The absorbance at a specific wavelength is found by Beer’s Law: Equation 2: A λ = c ει Equation 3: A λ total= ε 1 c ι 1 + ε 2 c ι 2 +... Absorbance is additive, meaning that the total absorbance at a certain wavelength in a
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This note was uploaded on 02/21/2010 for the course CHEM 11003 taught by Professor Stacy during the Spring '08 term at Berkeley.

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Light Inquiry Lab formal write-up - Light Inquiry...

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