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Recrystallization and Melting Point

Recrystallization and Melting Point. January 19. Purification and Characterization. Purification: separation of target compound from impurities Characterization Identity: Do I have what I think I have? Purity: How pure is the compound?. Recrystallization. Purification for solids

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Recrystallization and Melting Point

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  1. Recrystallization and Melting Point January 19

  2. Purification and Characterization • Purification: separation of target compound from impurities • Characterization • Identity: Do I have what I think I have? • Purity: How pure is the compound?

  3. Recrystallization • Purification for solids • Useful for • Large samples • Final purification step • Based on differential solubility

  4. Practical Aspects Impure Solid  Dissolve Recrystallize Filter www.whfreeman.com/mohrig3e then Movies and Spectra  Williamson Movies  5.3 Recrystallization (macroscale) (Also look at others, such as Drying Organic Liquids and Melting Points)

  5. Recrystallization: Theory • IMF in solids • Temperature dependence • Equilibrium process in slow crystal formation

  6. Important Points • Choice of solvent • Mixed solvents • Maintaining hot solvent • Safety when boiling • Hot filtration • Inducing crystallization • Washing crystals • Too much/too little solvent • Oiling out

  7. Melting Point • Physical property to characterize substance • Identity • purity capillary Melt-temp

  8. Theory and Application • Theory • Pure crystals and impure crystals • Intermolecular Forces • Lattice energy • Application • Depressed MP • Broad MP • Mixed MP Eutectic mixture

  9. Extraction Lab Question: How does the identity of an impurity affect the choice of extraction solvent? Techniques: Extraction, drying, evaporation, melting point

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