CH341L2(2)

CH341L2(2) - Emily Kaye and Peter Serafini CH341L 9/30/10...

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Emily Kaye and Peter Serafini CH341L 9/30/10 pKa of Methyl Red Introduction: The relationship between light absorption and concentration can be investigated according to the Beer-Lambert Law: A= ε l C. An experimental determination of ε can be performed using the absorption, A, and the concentrations of the acid and base components of a weak acid such as methyl red. Due to overlap in the absorption ranges, two equations are set up with two unknowns so that E can be solved based on the aborbances of the two buffers at two different wavelengths. The wavelengths are selected at the max aborbance of each of the two buffers. The goal of this experiment is to calculate the concentrations of the acid and conjugate base forms of methyl red, leading to the determination of the pKa of methyl red. Theory: Please see “pKa of Methyl Red” in the CH341 Lab Manual for theory and procedure. See attached sheets for relevant derivation Procedure: A .05% stock solution of methyl red was pre-made. This solution was created by dissolving 0.028g of methyl red in 20mL 95% ethanol in a 50 mL volumetric flask. Then, this was diluted almost to the mark, leaving room for the drop-wise addition of .1M NaOH to get all of the solid to dissolve. The volume was then brought to 50 mL, and 20 mL of this solution was put into a 200 mL volumetric flask, and 50mL 95% ethanol was added. Finally, this solution was diluted to the mark using water. A basic solution of methyl red was prepared by adding 10mL of 0.100 M sodium acetate in a 100 mL volumetric flask, and 10 mL from the methyl red stock solution and 9ml of 1.0 M potassium chloride were added. An acidic solution of methyl red was prepared by adding 10 mL of 0.100 M acetic acid, and 10ml from the methyl red stock solution
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This note was uploaded on 10/06/2010 for the course ES ES271 taught by Professor Machaut during the Spring '10 term at Colby.

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CH341L2(2) - Emily Kaye and Peter Serafini CH341L 9/30/10...

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