Delaney Chem162_FractCryst_Report_012812

# O in the crystals absorbance of the fephen 3 2

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O in the crystals Absorbance of the Fe(phen) 3 2+ complex at 510 nm Molar Absorptivity of ferroin, ε M -1 cm -1 Calculate the molarity of Fe 2+ from the absorbance (pathlength = 1 cm) Calculate the moles of Fe 2+ (moles of Fe 2+ = moles of (NH 4 ) 2 Fe(SO 4 ) 2 .6H 2 O) Calculate the molar mass (NH 4 ) 2 Fe(SO 4 ) 2 .6H 2 O) Calculate grams of (NH 4 ) 2 Fe(SO 4 ) 2 .6H 2 O in the crystals Mass KNO 3 crystals analyzed for purity (from Step B.8.) Calculate % mass of (NH 4 ) 2 Fe(SO 4 ) 2 .6H 2 O in the crystals Crystallization Number Summary: % Mass KNO 3 Recovered in Crystallization Steps Crystallization Number Mass KNO 3 Crystallized % of Original KNO 3 Mass Grams H 2 O used Molar Mass KNO 3 Grams KNO 3 Cryst. Temp, o C Solubility gKNO 3 /100 g water Molality KNO 3 K sp (Based on molality) H o Sol S o Soln Chem 162 Experiment #4 I. Fractional Crystallization of KNO3 with (NH4)2Fe(SO4)2.6H2O Impurity II. The Solubility Curve of KNO3 DATA, CALCULATIONS AND GRAPHS Part I: Fractional Crystallization of KNO3 with (NH4)2Fe(SO4)2.6H2O Impurity Does the absorbance exceed the desired range (0 to 2.0 A)? ___yes_________ If so, what dilution factor did you use in order to get the absorbance in the desired range? _______1:10______ II. Determining the Solubility Curve of KNO3 Results and Discussion 1. Do your results indicate that fractional crystallization works? Why or why not? My results indicate that fractional crystallization does work. Our percent impurity decreased from 11.38% to 2.06% to 0.58%%. This trend shows that with each crystallization, the percent impurity decreases. Therefore, fractional crystallization works as a means to remove impurities from a solution. 2. What is the disadvantage of fractional crystallization? The disadvantage of fractional crystallization is that with each crystallization and the riddance of impurities, the percent of the final product will decrease as well. This is because not every KNO3 molecule will crystallize, therefore loosing more and more produc each time. Also, no matter what, the final product will be impure, there is now ay to achieve an entirely pure compound, not to mention this process takes a very long time. 3. The Handbook of Chemistry and Physics list the enthalpy of solution of KNO3 as 34.89 kJ/mole. How does your value compare? Calculate the % error and discuss. abs(50.4kJ/mol-34.89kJ/mol)/34.89kJ/mol x 100% = 44.45% My value for enthalpy is pretty far off and our experimental value we obtained has a fairly large % error. Possible sources of error could be part of the solid being stuck to the stirring rod or the sides of the test tubes/beakers which would change the amount of solid in the solution. Also, it could have come from having innacurate measurements.
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