CHM3120C post lab 9.docx - CHM3120C Analytical Chemistry...

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CHM3120C Analytical Chemistry LabPost-Lab 9.Spectrophotometric Determination of Manganese and Chromium in MixtureIntroductionThe purpose of the following exercise is to utilize a spectrophotometric device to calculate the amount of manganese and chromium in the same mixture. When the solution is heated with persulfate in the presence of a silver catalyst the following equation is observed: Ag+2Cr3++ 3S2O82- + 7H2O ⎯⎯Cr2O72- + 6SO42- + 14H+ΔIt can be denoted that chromium ions in mixtures are oxidized to chromate. Meanwhile manganese in solution will also be oxidized by persulfate, periodate is also added to solution to form oxidation yielding the following equations: 2Mn2++ 5IO4- + 3H2O ⎯⎯2MnO4- + 5IO3- + 6H+ΔAg+2Mn2++ 5S2O82- + 8H2O ⎯⎯2MnO4- + 10SO42- + 16H+
4- Spectrophotometry is a highly useful tool when analyzing the composition of an unknown. A study performed by Scopes in 1974 was able to measure the amount of protein in a sample by analyzing their specific concentration of peptide bonds using a spectrophotometer. More recent studies performed by Paula, Henrique, Ricardo, Kuffel, Pretto, Engelmann, & Volken, utilized ultraviolet spectrophotometry absorption to measure the amount of selenium in population of biomass. Although being a complicated technique, spectrophotometry demonstrates to be a pretty useful tool in a variety of areas.Procedure and materials The materials for the following experiment included: 25 mL of unknownsolution, 50 mL of ~ 0.0021 M MnSO4 STD solution, 50 mL of ~ 0.0178 M K2Cr2O7 STD solution, 80 mL of conc. H2SO4, 3 g of solid potassium periodate (KIO4), 3 g solid potassium peroxydisulfate (K2S2O8), 3 mL of 0.1 M of AgNO3, Ocean Optics, Kimwipe and parafilm. The procedure started by obtaining two clean and dry 150 mL beakers and labeling them MnSO4 and K2Cr2O7. Previously prepared solutions were added to the beakers respectively. In a 100 mL volumetric flask; 50ml of .
distilled water and 2.8 mL of concentrated H2SO4 were added and diluted to the mark. The solution was labeled 0.5M H2SO4. The ocean optic device was set up and calibrated. Three 250 mL volumetric flask and three 250mL Erlenmeyer flasks

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