ACS Paper!!!! - Christina Lavelle ACS Paper Determination...

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Christina Lavelle ACS Paper Determination of Chemical Formula for Unknown Co Compound Abstract— In this semester’s Analytical Chemistry Lab, each individual synthesized a compound that contained Co, NH 3 , Cl, and H 2 O in unknown quantities. The purposes of the experiments performed were to analyze the created sample and determine the percentage of each molecule in the sample. A series of analytical methods were performed in order to complete this task. Each experiment was designed so that only one molecule was isolated from the whole and could be measured separately to determine percentage. The percentages of each ligand were then used to determine the empirical formula of the synthesized compound as well as the charge on each complex ion. Introduction— This experiment was designed to synthesize a compound with unknown quantities of cobalt, ammonia, chlorine, and water contents and then to determine the amount of each ligand using analytical procedures. In order to become more familiar with each of the procedures, quality control substances were used to practice the experiments. There were a series of experiments performed on the synthesized cobalt compound. First a gravimetric analysis was performed in order to determine the water content of the sample, where it is noted that the compound changed colors from red to purple, and then another analysis was performed to determine the chloride content of the sample. A gravimetric analysis entails heating a sample to a constant weight and then subtracting from the weight of the original sample to determine the percent of the molecule that is
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lost due to heating. To determine the percent of ammonia present in the purple cobalt compound, a Kjeldahl analysis was performed. This includes separating the ammonia from the sample by distillation and then titrating the distillates with bromocresol green indicator and a standardized HCl solution. Finally, the percent cobalt in the purple compound was found by a spectrophotometric analysis. This constitutes using a spectrophotometer to create a calibration curve and finding the concentration of a dilute solution made from the purple cobalt compound. Based on the conclusions to each experiment, it is expected that the empirical and general formulas for the purple and red compounds can be determined as well as noting the accuracy and precision of my results. Experimental— (1) Synthesis and Purification of Red Co Compound-- In this experiment, the Co compound was first prepared so that it may be analyzed. Approximately 18.0 grams of CoCl 2 6H 2 O and 12.0 grams of NH 4 Cl was dissolved in a 400mL beaker containing 60 mL of distilled water. Next, 55mL of concentrated aqueous ammonia and 14mL of 30% H 2 O 2 (one drop at a time) were added to the solution. While the solution was cooled in an ice bath, 120mL of concentrated HCl were added. The precipitate was collected using a Buchner funnel and washed with several 5mL portions of cold ethanol and then again with several 5mL portions of
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This lab report was uploaded on 04/09/2008 for the course CHEM 302 taught by Professor Fan during the Fall '07 term at Manhattan College.

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ACS Paper!!!! - Christina Lavelle ACS Paper Determination...

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