How does a separating funnel work


This video introduces the process of extraction, a separation method based on the different solubility of a compound in different solvents. The extraction of liquids and solutions with a separating funnel and of solids with the help of a Soxhlet apparatus is shown.

In the case of dissolved compounds, the use of a separating funnel, a tapered glass vessel with a Teflon stopcock and ground joint, is common. When extracting an aqueous phase, the target compound is obtained by adding an organic phase. In order to shorten the time until the solubility equilibrium is established, the closed separatory funnel is shaken. Particular attention must be paid to regular venting via the Teflon tap, as overpressure is usually created when shaking. The two phases can then be neatly separated from one another using the Teflon tap. Depending on the position of the solubility equilibrium, the extraction must be repeated several times. Higher yields can be achieved by multiple extractions with small amounts of solvent instead of a few extractions with large amounts. Since small amounts of water always remain in the organic phase after separation when extracting with water or washing with aqueous solutions, it is usually necessary to dry the solution over a water-binding substance such as magnesium sulfate.
Another method is necessary to extract mixtures of solids. A so-called Soxhlet apparatus is used for this, which consists of a Soxhlet attachment with a reflux condenser on a flask. First, a solvent in which the substance to be extracted is soluble is brought to the boil in the flask. This then condenses on the reflux condenser and drips into the extraction thimble in which the solid mixture to be separated is placed. The solvent with the dissolved components can get back into the flask via a side arm in the attachment. This process is a continuous extraction method and, when used correctly, results in the complete extraction of all soluble components.