chem lab 11 - 6. Absorbance is preferred to %transmittance...

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olorimetry m Lab section 25 07
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1. This lab was an exercise to find the concentration of an unknown diluted solution. The first part was basically finding the data we used to solve the mystery solution in part two. 2. Table 1 mL food color standard mL Water Concentration Concentration (drops/mL) % T transmittance Absorbance =2-log(%T) 0 (blank) 10 0 parts/ 10ml 0E-3 100 0 2 8 2 parts/ 10ml 2.4E-3 73.9 .132 4 6 4 parts/ 10ml 4.8E-3 59.8 .223 6 4 6 parts/ 10ml 7.2 E-3 48.9 .311 8 2 8 parts/ 10ml 9.6 E-3 42.2 .375 Table 2 Volume Color:gree n mL Water mL Solute Dilution Factor % Transmissio n Absorbance Concentration of Diluted Unknown Conc. Of Undiluted Unknown ID#: B 6 mL 4 mL 2/3 31.11 .508 4.8E-3 .0125 3. Graph and spreadsheet attached. 4a.) C =k/A k= 6.35E-3 C =6.35E-3/.508 C =.0125 b.) 4ml solute10ml water (12E-3)= 4.8E-3drops/mL 5. The absorbance is equivalent to 0 because vial number zero is our control, deionized water. Deionized water does not absorb photons of light and transmits 100% of light.
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Unformatted text preview: 6. Absorbance is preferred to %transmittance in spectroscopy, because absorbance is necessary to create a linear relationship. Absorbance= 2-log%transmittance. According to Beers law there is linear relationship between absorbance and concentration. As concentration increases, absorbance increases, and transmittance decreases. 7. The longer wavelength LED was used contrary to a shorter wavelength because this long low energy wave promoted greater absorbance in relation to shorter wavelength. Sheldon Pope Individual portion 12-5-07 8. The disadvantage of using a colorimeter is the precision factor; a spec 20 would be much more precise. The other disadvantage is a spec 20 calculates everything in the machine by itself. A spectrophotometer also can use wavelengths every twenty nanometers. This means the exact wavelength where the most absorbance of color can be found....
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This note was uploaded on 04/18/2008 for the course CHEM 403 taught by Professor Bauer during the Spring '08 term at New Hampshire.

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chem lab 11 - 6. Absorbance is preferred to %transmittance...

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