A separating funnel, also known as separation funnel, separatory funnel, or colloquially sep funnel, is a laboratory glassware used in liquid-liquid extractions to separate (partition) the components of a mixture between two immiscible solvent phases of different densities.
Typically, one of the phases will be aqueous, and the other a non-polar lipophilic organic solvent such as ether, MTBE, dichloromethane, chloroform, or ethyl acetate. Most organic solvents stay on top of an aqueous phase, important exceptions are most halogenated solvents.
A separating funnel has the shape of a cone surmounted by a hemisphere. It has a stopper at the top and stopcock (tap), at the bottom. Separating funnels used in the lab are typically made from borosilicate glass and the stopcocks are made from glass or Teflon. Typical sizes are between 50 mL and 3 L. In industrial chemistry they can be much bigger and for much larger volumes centrifuges are used.
To use the funnel, the two phases and the mixture to be separated in solution are added through the top with the stopcock at the bottom closed. The funnel is then closed and shaken very strongly to bring the phases into close contact. The funnel is then inverted and the tap carefully opened to release excess vapor pressure. The separating funnel is set aside to allow for the complete separation of the phases. The top and the bottom tap are then opened and the two phases are released by gravitation.