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Experiment 3 - E xperiment 3 Spectrophotometric Analysis of...

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Experiment 3. Spectrophotometric Analysis of Mixtures: Simultaneous Determination of Cr(III) and Co(II) Solutions Name: Kihong Lee Lab Partner: Daniel Hong Experiment Date: SEP 29 th , 2008, 2–6pm Experiment Location: 216, Latimer GSI: Orion Shih Section # 102 Abstract Spectrophotometric analysis is powerful tool to quantitatively investigate qualitatively known samples. In this experiment, we calibrated Cr(III) solution and Co(II) Solution between concentration and absorbance, using standard solutions. We first prepared 0.04M, 0.03M, 0.02M, and 0.01M of Cr(III) solution from 0.05M stock solution, and prepared 0.1M, 0.06M, 0.04M, and 0.02M of Co(II) solution from 0.1M stock solution. We measured the absorbance of each solution at the two different wavelengths, 410nm and 515nm, and used linear squares approximation to obtain the equation of the regression line. For Chromium, we obtained equations , = . ± . +- . ± . ACr 410nm 7 1 2 3c 0 006 0 065 and , = . ± . + . ± . ACr 515nm 2 6 2 3c 0 015 0 065 . For Cobalt, we obtained , ACo = . ± . + . ± . 410nm 0 161 0 037c 0 0028 0 0023 and , ACo = . ± . + . ± . 515nm 1 98 0 25c 0 007 0 016 . Using this result, we constructed simultaneous equations for concentrations of unknown solutions, and obtained the result of += . ± . - Cr3 0 039 0 018 mol∙L 1 and += . ± . - Co2 0 26 0 16 mol∙L 1 , in 95% confidence interval. We could quantitatively analyze the unknown sample using visible spectroscopy and various statistical tools. This experiment not only showed the great utility of UV-vis spectroscopy and Spectrophotometric analysis, but also revealed the possibility of further application, accompanied by qualitative analysis techniques. I. Introduction 1. Purpose of the experiment Spectrophotometric analysis is widely used and useful method for quantitative analysis of qualitatively known solutions. In other words, if we know what substances are included in a solution, we have powerful method called spectrophotometry to precisely measure the composition of that solution. Absorbance of certain matter at certain wavelength of light is directly proportional to the concentration of the matter, according to the Beer-Lambert Law. By finding relation coefficient between concentration and absorbance of standard solutions, we can utilize the absorbance of sample to know the concentration
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In this experiment, we tried to investigate the composition of aqueous Chromium (III) and Cobalt (II) solutions with unknown composition. At the same time, we managed to understand concepts, applications, and basic techniques of analytic chemistry and spectrophotometry. 2. Theoretical Background (1) Spectrophotometry Spectrophotometry is a study of spectra obtained from certain substances. This technique uses near-UV, visible light, and infrared lights for its utilization. In general, spectrophotometry is divided into UV-visible spectrophotometry, which uses near-UV and visible lights, and infrared spectrophotometry, which uses infrared lights, and we used UV-visible spectrophotometry in this experiment.
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