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Solubility and Extraction

Solubility and Extraction. January 17, 2012. Announcements. No lab this week Be prepared for lab next week Find handout on web Do pre-lab questions Write in your lab notebook—no manuals allowed No goggles, no lab! No notebook, no lab!. Solubility. “Like dissolves like”

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Solubility and Extraction

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  1. Solubility and Extraction January 17, 2012

  2. Announcements • No lab this week • Be prepared for lab next week • Find handout on web • Do pre-lab questions • Write in your lab notebook—no manuals allowed • No goggles, no lab! No notebook, no lab!

  3. Solubility • “Like dissolves like” • Based on IMF between different compounds

  4. Miscibility and Density • Miscibility spectrum • Density • Organics (0.7 g/mL) • Aqueous (1.0 g/mL) • Halogenated (1.3 g.mL)

  5. Miscibility with Water No Slightly Moderately Fully

  6. Separatory Funnel Separation of immiscible liquids

  7. Extraction • To pull out a compound from one layer into another • A compound partitions more toward where it is more soluble (equilibrium) • Partition coefficient • Multiple extractions may be needed to completely extract a substance

  8. Separation Using Extraction • What if our solid sample contains two substances? • When the solids dissolve and partition, there are three possibilities—which would be effective for a purification technique?

  9. Flowchart Extract  Separate  Dry  Evaporate

  10. Solubility • To plan for an extraction, must be able to choose proper solvents to separate impurities from target • Partitioning is based on relative solubility • Is the compound more organic soluble or more aqueous soluble?

  11. Solubility Rules of Thumb • Water soluble • Ionic • Organic ions of < 7-8 carbons • Small polar molecules • Organic compounds with one H-bond donor per 3-4 carbons

  12. Water Insolubility Spectrum • Somewhat soluble • Insoluble • Detergents

  13. Organic Solvent Solubility • Organic Soluble • Other organic molecules unless extremely different polarity • Organic insoluble • Ionic These are not organic soluble:

  14. Planning an Extraction • You want to separate the following two impurities from your target with extraction. You dissolve the mixture in water/ether in a separatory funnel. • Will the purification work? • In which layer is your target (top or bottom)?

  15. Acid/Base Extractions • Rather than neutral water, extract with aqueous acid or aqueous base • Acid/base reaction MIGHT occur with your target and/or impurity • Solubility changes due to ionization • Allows for better separations

  16. Extraction Revisited • You want to separate the following two impurities from your target with extraction. You dissolve the mixture in aqueous base/ether in a separatory funnel. • Will the purification work? • In which layer is your target (top or bottom)?

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