Transcription of EXPERIMENT 2: Recrystallization and Melting Point ...
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EXPERIMENT 2: Recrystallization and Melting Point ...
9 EXPERIMENT 2: Recrystallization and Melting Point Recrystallization (or Crystallization) is a technique used to purify solids. This procedure relies on the fact that solubility increases as temperature increases (you can dissolve more sugar in hot water than in cold water). As a hot, saturated solution cools, it becomes supersaturated and the solute precipitates (crystallizes) out. In a Recrystallization procedure, an impure (crude) solid is dissolved in a hot solvent. As this solution is cooled, the pure product crystallizes out and the impurities stay dissolved. General Recrystallization Procedure: 1) Choose an appropriate solvent(s) product is very soluble in it at high temperatures product is not soluble in it at low temperatures impurities are either soluble at all temps or insoluble at all temps (can be filtered off) 2) Dissolve impure so
•reported in the lab as a melting point range (usually 1–2 ˚C wide), not as a single temperature •used for: 1) characterization of a compound (also IR, NMR, mass spec.) 2) identification of an unknown (compare with known mp's) 3) determination of purity If a sample of a compound contains impurities, its mp is usually
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