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4: Extraction

  • Page ID
    93158
  • "Extraction" refers to transference of compound(s) from a solid or liquid into a different solvent or phase. In the chemistry lab, it is most common to use liquid-liquid extraction, a process that occurs in a separatory funnel. A solution containing dissolved components is placed in the funnel and an immiscible solvent is added, resulting in two layers that are shaken together. It is most common for one layer to be aqueous and the other an organic solvent. Components are "extracted" when they move from one layer to the other.

    • 4.0: Prelude to Extraction
      Organic solvents and colored aqueous solutions in separatory funnels
    • 4.1: Overview of Extraction
      "Extraction" refers to transference of compound(s) from a solid or liquid into a different solvent or phase. When a tea bag is added to hot water, the compounds responsible for the flavor and color of tea are extracted from the grounds into the water. In the chemistry lab, it is most common to use liquid-liquid extraction, a process that occurs in a separatory funnel.
    • 4.2: Uses of Extraction
      There are several reasons to use extraction in the chemistry lab. It is a principal method for isolating compounds from plant materials. Extraction moves compounds from one liquid to another, so that they can be more easily manipulated or concentrated. It also enables the selective removal of components in a mixture.
    • 4.3: Which Layer is Which?
      It is essential that you know whether the aqueous layer is above or below the organic layer in the separatory funnel, as it dictates which layer is kept and which is eventually discarded. Two immiscible solvents will stack atop one another based on differences in density. The solution with the lower density will rest on top, and the denser solution will rest on the bottom.
    • 4.4: Extraction Theory
      When a solution is placed in a separatory funnel and shaken with an immiscible solvent, solutes often dissolve in part into both layers. The components are said to "partition" between the two layers, or "distribute themselves" between the two layers. When equilibrium has established, the ratio of concentration of solute in each layer is constant for each system, and this can be represented by a value K (called the partition coefficient or distribution coefficient).
    • 4.5: Step-by-Step Procedures For Extractions
      Steps are given for a single and multiple step extraction protocol.
    • 4.6: Reaction Work-Ups
      A key step in conducting a reaction and isolate the product comes immediately after the reaction is complete, and is called the reaction "work-up" . The work-up refers to methods aimed at purifying the material, and most commonly occur in a separatory funnel. Solutions are added to the funnel to either extract or wash the mixture, with the goal of isolating the product from excess reagents, catalysts, side products, solvents, or compounds formed from side reactions.
    • 4.7: Acid-Base Extraction
      A modification of the extractions previously discussed in this chapter is to perform a chemical reaction in the separatory funnel in order to change the polarity and therefore partitioning of a compound in the aqueous and organic layers. A common method is to perform an acid-base reaction, which can convert some compounds from neutral to ionic forms (or vice versa).

    Contributor

    • Lisa Nichols (Butte Community College). Organic Chemistry Laboratory Techniques is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. Complete text is available online.