mod2 notes - Chemical Purification and Separation(Part 2...

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Chemical Purification and Separation (Part 2)
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Basic Techniques • Purification Techniques continued • Distillation – Vacuum Distillation – Steam Distillation • Chromatography – Column Chromatography – Thin Layer Chromatography – Gas Chromatography
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Vacuum Distillation • Distillation under reduced pressure is called vacuum distillation. • Used for distilling high-boiling or heat- sensitive compounds. • Takes advantage of the fact that the boiling point of a liquid is a function of pressure.
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Vacuum Distillation • Disadvantage of vacuum distillation is that it is less efficient. • Partial vacuum can be obtained using a vacuum pump or water aspirator. • Vacuum pumps can produce pressures as low as 0.5 Torr where water aspirators produce pressures around 13 Torr.
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Vacuum Distillation
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Vacuum Distillation
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Steam Distillation • Steam distillation is the distillation of a mixture of water (steam) and an organic compound or a mixture of organic compounds. • The organic compound must be immiscible with water.
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Steam Distillation • Immiscible mixtures like these do not behave like solutions. • The components of an immiscible mixture will boil at a lower temperature. • Steam distillation is commonly used as a way to remove natural products from their naturally occurring matrix.
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Steam Distillation • P total = P° A + P° B • The boiling point of the liquid will be lower than the boiling point of any component of the mixture. • The component to be isolated must have a higher vapor pressure than the rest of the components of the mixture.
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Steam Distillation • Boiling behavior for immiscible mixtures differs than the behavior for miscible mixtures. • For miscible mixtures: P Total =X A A +X B B • For immiscible mixtures the mole fraction of the components are not needed.
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Steam Distillation • In a steam distillation of two immiscible liquids, the number of mole of each component in the vapor, and eventually in the distillate, is proportional to the vapor pressure of the pure component. • For steam distillation moles of A = P°A moles of B P°B
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Steam Distillation
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Chromatography • Chromatography is a separation technique that exploits the differences in partitioning behavior between a mobile phase and a stationary phase to separate the components of a mixture. • Mobile phase consist of a liquid or a gas. • Stationary phase usually a solid or a liquid.
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Chromatography • Three types of chromatography commonly used by organic chemists are: • Column chromatography • Thin layer chromatography • Gas chromatography
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• The components of a mixture separate because of differences in their affinities for the stationary phase and their solubilities in the mobile phase. • The mixture to be separated is placed on
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mod2 notes - Chemical Purification and Separation(Part 2...

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