The separatory funnel

The separatory funnel is a piece of glassware used in the method of liquid-liquid extraction.

Figure: Separatory funnel with stopper and stopcock.

How to use a separatory funnel:

Fill: to fill the separation funnel remove the stopper, add a funnel. Make sure the funnel is placed over a beaker or flask and the stopcock is closed. Then pour in the two phases, proceed to remove the funnel and replace the stopper.

Shaking: if the purpose is to move a substance from one phase to the other mixing is required. When the two phases are in the funnel, a gentle shaking will temporarily make the phases “mix” enlarging the surface between the phases, ensuring the largest surface possible for the compound of interest to migrate from one phase to the other. When doing so, a slight gaseous pressure can build up, to avoid it making a mess, the funnel must be vented.

Venting of a separatory funnel is needed to ensure no build-up of gasses could cause an unintended push out of the stopper or liquid. While holding the stopper gently turn the separatory funnel so the pointy end points upwards away from any people or important lab equipment. Then proceed to turn the stopcock to slowly vent any gas from the separatory funnel. Continue the shaking and venting until no audible sound can be heard.

Stopcock: the stopcock is a small valve structure at the bottom of the separatory funnel which is used to vent out gas and slowly release a single phase at a time into a new container.

Stopper: the stopper functions to keep the liquid in the separatory funnel in cases where it is held upside down, and to avoid any splashing.