Solvent Extraction

Liquids that form two layers when mixed provide an opportunity for purification of materials that prefer one layer more than the other. For example, many organic chemicals are liquids that are very non-polar and separate from water because it is quite polar. Benzene mixed with water, shaken, and allowed to stand will result in a layer of benzene on top of a layer of water. If the water originally contained some non-polar material such as butanol, shaking with benzene would result in a benzene layer rich in butanol.

At equilibrium, the activities of the dissolved material must be the same in each phase. We can approximate activity with concentration to get the definition of distribution coefficient :

  • How pH affects polarity.,
  • Numerical examples,
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  • Digression about environmental engineering.
    while on sabbatical leave, ESB, Porto, Portugal July 1996