Lab 23

Katissa Williams
Feb. 19, 2011
Chem 221
Title: Purifying Acetanilide by Recrystallization
Introduction
Recrystallization is a widely-used techniques to purify a solid mixture. The desired product is isolated from its impurities by differences in solubility. Insoluble impurities and colored impurities can be removed from hot solvent through the use of activated carbon and filtration. Soluble impurities remain in the cold solvent after recrystallization. The desired product should be as soluble as possible in hot solvent and as insoluble as possible in cold solvent. The selection of solvent is, therefore, critical to the successful recrystallization.
The purpose of this experiment is to select a suitable recrystallizing solvent, to be able to purify and separate acetanilide from the mixture by process of recrystallization, and to compare melting points of recrystallized and impure acetanilide. It would be beneficial to have prior understanding of how to measure mass in milligrams, volume in milliliters, and to measure melting points.
Organic compounds that are synthesized in lab or isolated from natural resources have been tainted by impurities. Recrystallization is a process that removes impurities from solid organic compounds that are at room temperature. This process is built on the principle that the solubility of a compounds increases with temperature and decreases as it cools down, into its crystal form.
Pure compounds can be made by recrystallization. A small pure seed crystal of the compound forms in the solution as it cools down after being heated. Additional molecules are attached to the crystals in uniform layers, forming a growing crystal lattice. Crystal molecules have a higher affinity for the same kind of molecules than impurities. This process of crystallizing removes one kind of molecule from the solution.
Choosing a recrystallizing solvent
A good solvent for crystallization depends entirely on the polarity of the solid you’re trying... [continues]

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