Separatory Funnel

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A separatory funnel is useful for performing extractions. Extraction is one way of purifying a substance. In an extraction, a solute is transferred from one solvent to another. One type of extraction involves removing polar solutes from an organic solvent that is immiscible with water. The organic solution and water are added to the separatory funnel, shaken, and allowed to separate into layers. The polar molecules preferentially dissolve in the water, and because the organic solvent and the water are immiscible, the water layer may be separated from the organic layer. By this process, a polar compound can be isolated from impurities, which remain in the organic phase.

Always work with a beaker below the separatory funnel. If a leak occurs or the stopcock falls out, the beaker will collect any solution that spills.

Add the sample solution and the extraction liquid to the funnel.

Video: Pouring in liquids ( 2.90 M ) Text description

Next, mix the two liquids must be thoroughly. Mixing the liquids may cause pressure to build up in the funnel, so periodically venting the gas in the funnel by opening the stopcock while the funnel is inverted.

Video: Mixing the liquids ( 8.12 M ) Text description

When venting the funnel no longer produces a hiss of escaping gas, the two liquids have been thoroughly mixed. Place the separatory funnel back into the ring stand and immediately remove the stopper. Why?

When the liquids have cleanly separated into two distinct phases, the bottom liquid may be drained from the separatory funnel.

Video: Draining the lower phase ( 3.44 M ) Text description

The next steps of the extraction depend on whether the solute you are trying to isolate was in the top layer or the bottom layer of the liquids originally in the separatory funnel.

Video ( 2.31M ) What did the student using the separatory funnel forget to do? Answer

Occasionally, emulsions can form while the liquids are being mixed in the separatory funnel. An emulsion occurs when small droplets of an organic solvent are suspended in a water solution. Emulsions can be difficult to disperse, however, a few techniques may be attempted.

If the solutions that will be mixed in the funnel are known to emulsify, be careful to perform all the steps in the extraction very slowly and gently.

Once an emulsion has formed, first try slowly and gently swirling the solution in the separatory funnel.

Video: Slow & gentle swirling ( 1.11 M )

If the emulsion does not disperse, next try adding a small amount of saturated aqueous sodium chloride or water soluble detergent solution to the liquid in the separatory funnel.

Video: Addition of NaCl ( 713K )

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