Chemistry Experiment 4

Chemistry Experiment 4 - Experiment 4: Spectrophotometric...

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Experiment 4: Spectrophotometric Determination of Metal- Ligand Complex Composition. By Jennifer Knotts Lab Partners: Katlin Geldbach Chemistry 1312, Section F-1, February 15, 2007
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Introduction: The lab was preformed to provide a study of spectrophotometric determination and provide experience in proper volumetric and mole ratio calculations. The absorbance of a solution is proportional to the concentration of any colored species that absorb wavelengths presented in that example. The relationship between absorption and wavelengths is referred to as Beer’s law. Beer’s law is given by A = ε bc; where A= absorbance; ε = molar absorptivity; b = path length; and c = concentration. Measurement of absorbencies can also be calculated using an instrument called a spectrometer or colorimeter. In order to calculate absorbency, the measurement absorbance of each solution is plotted against the ratio of moles of ligand/moles of metal. From the mole-ratio plot the molar absorptivity: As well as the determination of number of ligand bonds and the equilibrium constant can be determined. Purpose: The overarching goal of these procedures is to determine the equilibrium constant of formation and chemical formula of a complex of iron(II) ions (Fe 2+ ) and the bipyridine molecule (C 10 H 10 N 2 ). In this laboratory experiment, proper use of volumetric and Mohr pipettes was of critical use, and procedural modifications were taken in account to ensure that each participant would be required to demonstrate proper use of volumetric equipment. In addition, introduction to the use of ultraviolet visualization techniques of prepared chemical samples was expected to independently interpret computerized readouts of spectrophotometer-generated data. Finally, all data was recorded and the necessary calculations were carried out. Procedure: “Procedure: The procedure was adapted from the online lab manual for the Georgia Institute of Technology Chemistry Course 1312: “Metal-Ligand Composition by Mole-ratio method” by Dr. Leigh Bottomley, page 1-4 with the following changes.” Each student-scientist was required to prepare ten necessary test tube solutions through use of either a volumetric pipette or a Mohr pipette with a pipette bulb in order to develop proper laboratory skills with the necessary equipment.
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Data: Absorbance Readings for Prepared Iron(II)-Bipyridine Solutions Beaker Iron (II) Soln. (mL) Bipyridine Soln. (mL) Buffer pH 5 (mL) Hydroxyamine 1% (mL) Water (mL) Absorbance* 1 1 1 7 1 0 0.371 2 1 1.5 6.5 1 0 0.521 3 1 2 6 1 0 0.676 4 1 2.5 5.5 1
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Chemistry Experiment 4 - Experiment 4: Spectrophotometric...

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