Recrystallization and melting point
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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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Purification and characterization
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
Recrystallization

  • Purification for solids

  • Useful for

    • Large samples

    • Final purification step

  • Based on differential solubility


Practical aspects
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)


Recrystallization theory
Recrystallization: Theory

  • IMF in solids

  • Temperature dependence

  • Equilibrium process in slow crystal formation


Important points
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


Melting point
Melting Point

  • Physical property to characterize substance

    • Identity

    • purity

capillary

Melt-temp


Theory and application
Theory and Application

  • Theory

    • Pure crystals and impure crystals

    • Intermolecular Forces

    • Lattice energy

  • Application

    • Depressed MP

    • Broad MP

    • Mixed MP

Eutectic mixture


Extraction lab
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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