OCHEM The Recrystallization of Benzoic Acid 2

OCHEM The Recrystallization of Benzoic Acid 2 - The...

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The Recrystallization of Benzoic Acid Lindy Hilpert Brad Hutnik Organic Chemistry 330 September 19, 2007
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Introduction: The purpose of this lab was to recrystallize the benzoic acid that was extracted in the last lab and to determine the percent recovery. Theory, Reactions, and Mechanisms: Recrystallization is a process of purifying non-volatile solid organic compounds. Recrystallization is based on the concepts that a compound is always more soluble in hot solvents than cold solvents, molecules have unique solubility properties, and a forming crystal will only accept similar substances into its lattice. The process of recrystallization starts with dissolving the substance in the appropriate hot solvent. The correct solvent is characterized by the substance dissolving in it when it is hot, but not when it is cool (room temp). The solvent must also dissolve the impurities in the substance so that they do not adhere to the purified substance when it is recrystallizing. The solvent cannot chemically react with the substance to be purified, it can only dissolve it. Another important property is that the boiling point of the solvent must be lower than the boiling point of the solute. If it is higher, then the solute will melt instead of dissolving, and it will oil out. The solvent needs to be volatile so that it can be evaporated off of the crystals in the end. The final characteristic is that it should be inexpensive. Once the appropriate solvent has been chosen, it is boiled and added to the solute. Only enough solvent to dissolve the solute is needed. If too much is added, the amount of crystals that come out will not be a maximum. When the solvent is added to the solute, there is so much heat involved that the solvent and solute molecules collide, and the solute molecules dissolve in the solvent. The solvent molecules surround the solute molecules and stabilize them in solution.
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The solution is then allowed to cool so that the solute starts to recrystallize out of solution. This occurs because of the crystal lattice theory. Crystal lattice theory states that a growing crystal will only accept similar entities into its lattice. The lattice starts to
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OCHEM The Recrystallization of Benzoic Acid 2 - The...

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