Extraction, distillation, and chromatography separation techniques and when each applies, tested on the MCAT.
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- What is the purpose of liquid-liquid extraction?
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To separate compounds based on differing solubility in two immiscible solvents.- "Like dissolves like" - what does this principle predict about solubility?
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Polar compounds dissolve best in polar solvents; nonpolar compounds dissolve best in nonpolar solvents.- In extraction, the ____ describes the ratio of a solute's concentration in the organic layer to its concentration in the aqueous layer at equilibrium.
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partition coefficient- In a separatory funnel, which layer settles on the bottom?
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The denser layer.- Is diethyl ether denser or less dense than water?
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Less dense (it forms the top layer).- Is dichloromethane (DCM) denser or less dense than water?
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Denser (it forms the bottom layer).- In acid-base extraction, how can a neutral amine be separated from a neutral organic compound?
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Treat with aqueous HCl to protonate the amine into a water-soluble ammonium salt, moving it into the aqueous layer.- In acid-base extraction, how can a carboxylic acid be separated from a neutral organic compound?
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Treat with aqueous NaOH to deprotonate it into a water-soluble carboxylate salt, moving it into the aqueous layer.- After extracting a protonated amine into the aqueous layer, how do you recover the free amine back into an organic solvent?
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Add a base, such as NaOH, to deprotonate it, then re-extract with organic solvent.- What is "salting out" in the context of extraction?
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Adding a salt, such as NaCl, to the aqueous layer to increase ionic strength and reduce the organic compound's solubility in water, improving extraction efficiency.- Why is a drying agent such as anhydrous magnesium sulfate added after extraction?
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To remove residual water from the organic layer.- Why are several small-volume extractions more effective than one large-volume extraction using the same total solvent?
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Multiple small extractions remove more total solute than a single extraction with the same overall volume.- What physical property does distillation use to separate compounds?
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Boiling point (volatility).- When is simple distillation an appropriate technique?
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When the boiling points of the components differ by more than about 25 degrees C, or one component is nonvolatile.- When is fractional distillation preferred over simple distillation?
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When the boiling points of the components are close together, less than about 25 degrees C apart.
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