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Narration : 9. Separating Funnel

• The separating funnel is used when organic compounds are extracted from an aqueous solution with organic solvent.
• This method is also used when removing acid or base dissolved in organic solvent into aqueous solution in the form of salt.
• This experiment will explain the extraction of the amine from water with ethyl ether by the separating funnel.
• Place an erlenmeyer flask under the separating funnel.
• Check that the stopcock is tightly closed.
• Then, add the sample solution into the separating funnel.
• Next, add ethyl ether.
• Further, add a small amount of ethyl ether to the sample flask and wash out.
• Here if excess amounts of solutions are used, organic phase and aqueous phase will not be in contact with each other.
• Wet the stopper with water for tight fitting.
• First, put the stopper in and also close the pressure releasing hole.
• Next, pressing the stopper with the palm turn the separating funnel upside down.
• Release the internal pressure by opening the stopcock immediately.
• The internal pressure often rises when the separating funnel is shaken for the first time, so after light shaking, the stopcock should be opened to release pressure.
• Gradually shake vigorously to mix well organic phase and aqueous phase.
• Remember to open and close the stopcock regularly to release the pressure.
• Place the separating funnel on the stand and release the stopper.
• After a while the top layer of ethyl ether and the bottom aqueous layer will separate.
• It should be noted that in the case of organic solvents with heavier specific gravity like chloroform, the organic phase will form the bottom layer.
• Open the stopcock to allow the aqueous phase to pour into the erlenmeyer flask.
• When most part of the aqueous phase is transferred into the erlenmeyer flask, operate the stopcock carefully, and close it just before the interface touches its edge.
• Pour out the remaining organic phase into another flask through the top tap.
• Pour the aqueous phase back into the separating funnel.
• Next, add new organic solvent and repeat the procedure.
• If the material is easily soluble in the organic solvent, it is enough to repeat the procedure 2 or 3 times.
• To remove water from the extracted organic phase, it should be washed with brine.
• Finally, an appropriate amount of drying agent is added to the extracted solution and the dissolved water is removed as crystalline water.
• Increase in internal pressure needs to be taken care of especially during the process of extracting acids from organic solvent with saturated sodium bicarbonate solution.
• It is important to release the carbon dioxide produced, or it could be dangerous.
• Such use of the separating funnel is a faulty example.
• If the stopcock is left open, the solution will run out. Not only should the stopcock be checked but an erlenmeyer flask must always be placed under the separating funnel.
• If the pressure releasing hole is left open the solution will leak out through it when turned upside down. Always check that the hole is closed before turning.
• When the stopcock is opened there are chances that the solution will spurt out. Hence the tip of the separating funnel must never be pointed at anyone around or yourself.
• Some separating funnels have a glass stopcock. In this case, wet the stopcock with water beforehand for smooth usage.
• If the stopcock is left as it is after usage, there are chances of it hardening. Immediately remove the cock after usage and store it after washing well.