Using the flasks each of the solutions were diluted

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flasks. Using the flasks, each of the solutions were diluted to the mark with deionized water. For chromium, aliquots of 10, 15, and 25 mL of the standard were placed into 250 mL volumetric flasks. Then, 10 mL of concentrated H2SO4 was added to the solutions, followed by deionized water which brought the solutions to the mark. Following the boiling and dilution of the mixtures, the absorbance of each solution was taken at 440nm, and then at 545nm, while using H2SO4 as the blanksolution. An Excel spreadsheet was then used to plot absorbance vs. concentrationin units of mg/L. 25 mL of the unknown solution was obtained from the teacher’s assistant and placed in a 250 mL volumetric flask. The solution was then diluted to the mark with deionized water. Following this step, 50 mL aliquots of the unknown were placed into three different Erlenmeyer flasks, and 5 mL of concentrated H2SO4 was added to the mix. 1 mL of .1 M AgNO3 was added to the solution, along with 1g of solid potassium peroxidisulfate. The solutions were then heated to boiling for 5 minutes. The solutions were allowed to cool and then .5g of KIO4 was added, followed by 5 minutes of additional heating. The solutions cooled to room temperature, and then diluted to the mark in a 250 mL volumetric flask. Finally, the ppm of Cr and Mn ions in solution were calculated using Beer’s law.4
III. ResultsVariablesControl: volume of each aliquot used in each trial, wavelengths used to test absorbance, x and y intercept of the plotsIndependent: concentration of the standard solutionsDependent: concentration of Mn in the standardized solution, concentration of Cr in the standardized solution, concentration of each aliquot in each trial, absorbance of the solutions at 440nm, absorbance of the solutions at 545nm, k values of manganese and chromium, absorbances of the unknown solutions, concentration ofmanganese and chromium in the unknown, average concentration of manganese, average concentration of chromiumQualitative ObservationsEach of the three manganese solutions were transparent before the addition of heatFollowing boiling, each of the solutions turned pink in color, the more concentrated the sample, the darker the purple wasEach of the three chromium solutions appeared pale yellow in color, the most concentrated solution was the darkest shade, and the least concentrated was lightest in shade.Quantitative observations Conversion of g/L into Molarity.1602 g/500ml x 2/2 = .3204g/L(.3204g) / (151.0 g/mol) = .002122 MConcentration of Mn in standardized solution5
= (Molarity x molecular weight) x 1000116.6 mg/L = (.002122 x 54.94 g/mol) x 1000*concentration of Cr in standardized solution was found using the same method*Concentration for each aliquotC1V1 = C2V2(116.6mg/L)(.01000L) = (C2)(.25L)4.660 mg/L = C2*concentration of each of the aliquots for both standard solutions was found in the same way*Values for k were obtained from the plotsConcentration of Manganese in the unknown 250ml flask (trial 1)

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