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Funnels

Separation Funnels

Separatory funnels, or separation funnels, are a common fixture in chemistry labs. These funnels are used to separate immiscible liquids from their solutes. The funnel is usually glass, pear-shaped, and usually includes a stopper and a stopcock.

Separatory funnels work on the principle that immiscible liquids will separate from each other naturally along with their solutes, creating different layers of solution-solute. For example, a non-polar solute can be extracted from a solution by mixing it with a non-polar solvent in a separation funnel. After initial mixing, the initial solution and non-polar solvent will separate and the solute will be in the new solvent. These layers can be separated in perpetuity by draining them from the separatory funnel using the stopcock to control the flow.

The layers will separate in the funnel based on their relative densities, with the lowest density liquid above higher densities. However, it is important to not assume that the bottom layer in a separatory funnel is always the aqueous solution; while most organic solvents are less dense than aqueous solvents, processes such as halogenation may cause exceptions to this rule. For these reasons, it remains necessary to choose the right solvents for the separation.

Always use proper technique when using a separatory funnel. For example, mixing should generally be done by gentle inversion when the stopper is secure and the stopcock is closed. Venting should be done with the stopcock pointed to the back of the hood. Finally, always use appropriate protective gear while working in any laboratory setting.