Experiment #2: Liquid-Liquid Extraction

Do not dry your samples in the hood on a plastic dish. The air suction has a tendency to "suck up" powdery compounds. If you leave your samples to dry in the hood put them in a large beaker. Do not cover the beaker. You may want to dry them in your drawer. However, this tends to make your drawer smell bad the rest of the semester. Another alternative may be to ask the instructor to designate a "safe drying area" to dry student samples. (jbf)

Make sure to separate the layers very well. Poor separation results in small ppts forming, meaning that a decent recovery is not possible. Poor separation can also mean that a ppt forms in a layer in which it should not appear, meaning that one could use the wrong layer for recrystalization. JM

before you come to lab, determine which layer your product will be in after each extraction.  Also make sure you know the densities of the two layers so you know which will be on top.  This will help to ensure you don't accidentally dump out your product. SP

Make sure not to shake your funnel to hard or you stopper may fly off and also to take the stopper off when draining your product. If you don't your product will not drain out as fast. KM

When performing the liquid/liquid extraction, read the labels of the solutions you are adding to your unknown mixture very carefully!  It is very easy to confuse 1M NaOH with 10M NaOH . If you accidently add the 10M NaOH when you should add the 1M  it causes major problems in the experiment.  Save yourself the trouble and double, triple check the labels. EP

Make sure you thoroughly mix your solutions. If you do not this can decrease your expected % recovery. EC

Make sure you vent the separatory funnel enough times for the amount of mixing that you perform. If you mix the contents, but do not vent properly, you run the risk of the pressure building up and the funnel cracking or the top coming off. It might be a good idea to practice the liquid/liquid extraction technique with some water in the funnel before you begin. PH

Before performing liquid/liquid extraction be sure to thoroughly clean out your sep funnel.  This lab depends on proper mixing and accuracy; any remnants of a liquid left in the funnel can affect your separation and in turn your % recovery. AK

when using vacuum filteration to make sure you hold onto the flask or have it clamped down to something before turning on the vacuum or else your solution and flask will tip over from the pull of the vacuum and to make sure to break the seal between funnel and flask or else water will be sucked back into the flask. PL

In addition to Pete's tip about vacuum filtration: set up the apparatus and then turn suction on. When beginning to pour the liquid into the filter, pour very slowly! If you pour too fast you might dislodge the filter paper and let some of your solid through the holes in funnel. This will be messy and a hassle to redo. PH

Make sure that the stopper you use is the correct size. One might appear to be the right size but when you start shaking, no matter how tightly you hold the stopper in place, you're bound to lose some liquid! MW

After shaking your separatory funnel to define the layers, when venting, definitely vent it away from anything important (ie, face). The pressure spews some liquid out and you do not want any of that near/on you. CR

In this experiment, it is important to record every observation and write down the % recovery from the unknown mixture. AP

Become acquainted with the research you did for your prelab write up. Especially the safety info for the chemicals used. Handle the dangerous ones carefully!!! YM

When setting up your Buchner Funnel, make sure that you get a tube wide enough to fit the vacuum trap and funnel or you will waste time just trying to fit the tube onto the funnel or vacuum trap. Also when shaking the sep funnel, make sure your stopcock is actually closed or your liquid will leak out. MFL

This is in addition to the post made about removing the stopper once you begin extraction.  Another reason to do so is to prevent air bubbles from going back into the solution (believe me, it happened).  When this happens, the layers remix and defeats the purpose of the initial separation. KS