Experiment 10 - ₃ ₂ H O = 18 g/mol ₂ Actual 291 g/mol...

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Chem 1151 Sec 3 Expt 10: Determining the Concentration of a Solution: Beer’s Law November 12, 2007 Purpose: To determine the concentration and formula of an unknown cobalt nitrate solution. I. Data: Standard Solutions: CoCl ∙ 6H O Trial Concentration (g/L) Molarity (M) Absorbance
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1 8.0 0.034 0.110 2 16.0 0.067 0.213 3 24.0 0.101 0.307 4 32.0 0.134 0.414 5 40.0 0.168 0.505 Unknown Solutions: Co(NO ) ∙ nH O ₃ ₂ Trial Concentration (g/L) Molarity (M) Absorbance Molar Mass (g/mol) 1 15.4 0.071 0.205 217 2 21.0 0.096 0.272 219 3 25.0 0.110 0.325 227 Trial Percent Error 1 18.6 2 19.7 3 24.0 II. Observations: A relationship between the absorbance and the concentration was seen. The absorbance would increase when the concentration value increased. The solutions of higher concentration were darker than those with a lower concentration. More light is allowed through the solutions with a lower concentration, therefore, more light is absorbed with solutions of higher concentrations.
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III. Calculations: Co(NO ) = 183 g/mol
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Unformatted text preview: ₃ ₂ H O = 18 g/mol ₂ Actual: 291 g/mol – 183 g/mol = (108 g/mol)/(18 g/mol) = 6 Experimental: Trial 1 = 291 g/mol – 217 g/mol = (74 g/mol)/(18 g/mol) = 4 Trial 2 = 291 g/mol – 219 g/mol = (72g/mol)/(18 g/mol) = 4 Trial 3 = 291 g/mol – 227 g/mol = (64 g/mol)/(18 g/mol) = 4 IV. Conclusions: The concentrations of the unknown solutions were found to be 15.4 g/L, 21.0 g/L, and 25.0 g/L. The formula found after calculations was closest to a trihydrate, but it should have been a hexahydrate like the first solution. There may have been flaws due to some confusion of finding the concentration of the unknown solutions. The bottles containing the solutions stated a value that may have been the concentration, but the values of absorbance recorded would not have matched. The absorbance readings appeared to be correct because the values increased as the concentration increased....
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This note was uploaded on 04/17/2008 for the course CHEM 1151 taught by Professor Splan during the Fall '07 term at University of Minnesota Duluth.

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Experiment 10 - ₃ ₂ H O = 18 g/mol ₂ Actual 291 g/mol...

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