Beer's Law - BCC Chemistry 161 Experiment 10 Background...

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BCC Chemistry 161 O 3 S N N HO SO 3 OCH 3 H 3 C C 18 H 14 N 2 O 8 S 2 Experiment 10 Beer’s Law : Determining the Concentration of a Solution Background Color additives are used in foods for a variety of reasons. Sometimes they are used to compensate for the natural color loss of food during storage or exposure to light or air. Sometimes they are used to enhance natural colors because off-colored foods are often mistaken for being lower in quality for example, perfectly good oranges that are naturally dull orange/brown are sprayed with Citrus Red No. 2 to make them more appealing. Color is also introduced to what are otherwise colorless products, such as strawberry frosting and key lime pie. A green key lime pie is more likely to be purchased by consumers than a beige one! 1 In 1900, there were about 80 man-made food dyes available to consumers. Due to standards in improving food safety, seven color additives were approved by the FDA (Food and Drug Administration) for use in foods. 2 Allura Red (FD&C Red No. 40) is one of the seven color additives certifiable for food use by the US Food and Drug Administration (FDA). (FD&C means Food, Drug and Cosmetic certified). Other dyes are permitted for drug and cosmetic use only (D&C) and external drug and cosmetic (external D&C). The safety of food dyes is rather controversial. Research has shown very little risk to humans in the consumption of approved dyes but that doesn’t guarantee there are no adverse effects in the population. Some consumers claim to have a sensitivity to artificial colors and flavorings and others believe the consumption of artificial colors is linked to hyperactivity or 1 From the U.S. FDA/IFIC brochure, “Food Color Facts” (Jan 1993) http://www.cfsan.fda.gov/~lrd/colorfac.html accessed August 28, 2008. 2 In addition to the seven, there are two additives that are restricted to specific uses. learning disabilities in children. Without substantial evidence to support these claims, it is up to the public to use caution and good judgement in consuming color additives, as for any substance. This experiment will give you the opportunity to quantify the amount of a color additive in a common product, Kool- Aid. Is it a lot of food coloring? You’ll find out! Principles of Colorimetry The primary objective of this experiment is to determine the concentration of a common food-dye, Allura Red, in Kool-Aid using Beer’s Law and a technique called spectrophotometry (colorimetry). The Beer-Lambert Law states that the absorption of light by a substance is proportional to its concentration in solution: A = l c where A is the absorbance (unitless), is the molar absorptivity coefficient (M -1 cm -1 ), l is the pathlength of the light through the cuvette (cm), and c is the concentration (M).
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BCC Chemistry 161 Experiment 10 Beer’s Law: Determining the Concentration of a Solution The Allura Red solution used in this experiment has a red color. You will be
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This note was uploaded on 12/08/2009 for the course CHEM 151 taught by Professor Staff during the Fall '08 term at University of Arizona- Tucson.

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Beer's Law - BCC Chemistry 161 Experiment 10 Background...

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