Lab 2 - Recrystallization

Lab 2 - Recrystallization - The Recrystallization of...

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The Recrystallization of Benzoic Acid Chemistry 0330 Hikmat Daghestani Lauren Allen 9/17/07
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Introduction The purpose of the experiment was to explore the concept of purification of the Benzoic Acid that was previously extracted with the use of charcoal and gravity filter techniques (if necessary), and to then form pure Benzoic Acid crystals. It was also to explore the three basic principles involved in the process of recrystallization. Reactions/Mechanism/Theory Recrystallization is a purification technique for non-volatile solids. Recrystallization involves a solute that has impurities and a solvent that the solid (solute) will dissolve readily into when the solvent is hot and will not dissolve into when the solvent is cold. However, the impurities in the solute should stay dissolved at colder temperatures. The solvent must also have a boiling point that is less than that of the solid so the solid doesn’t melt, it disassociates. The solvent must also be unreactive with the solute and the solvent must be volatile, so it is easy to get rid of. Recrystallization has three beginning steps: collision, dissociation, and solvation (as seen in the figure below). Collision and dissociation happens when the temperature is high enough for the solute to dissolve. The solvent molecules will collide (the hotter the temperature the more kinetic energy involved in the collisions) into the solid molecules and dissociate them from each other. This also frees up the trapped impurities. Solvation is the surrounding of the solvent molecules around the solute and impurity molecules keeping them from sticking back together. The solvent/solute mixture is then slowly cooled to prevent the impurities
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This note was uploaded on 04/14/2008 for the course CHEM 0330 taught by Professor Forget during the Fall '07 term at Pittsburgh.

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Lab 2 - Recrystallization - The Recrystallization of...

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