distill - Chem 267. Distillation. (rev 7/10). Liquid...

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Chem 267 . Distillation . (rev 7/10). Liquid substances are most often purified by distillation. In the first part of this experiment, to practice the techniques, you will separate a mixture of cyclohexane and toluene (tol-u-ene) by simple and fractional distillation and compare the two methods. In the second part of this experiment, you will distill an unknown mixture and (1) determine the identity of the components by observing their boiling points (BPs), and (2) determine the relative amounts of each by measuring the amount of distillate collected at each BP. The purity of each unknown will be checked by gas chromatography (GC). The most difficult part of distillations is setting up the small apparatus properly and attaining a slow steady heating rate. Take your time to do it correctly. You will use this technique in several experiments later on. Do Prelab Exercise a.) on p. 86 as part of your prelab outline. Note that the procedure to follow is that given below and not that given in the Distillation chapter of the lab text. The lab text should be used for reference. Simple Distillation of Cyclohexane and Toluene . Because the electrically heated sand bath takes time to reach operating temperature, turn it on to a setting of about 30 as soon as you enter the lab. For a sketch of the apparatus, refer to Fig 5.5 in Williamson but note the modifications given in this handout. Check the 5 mL round bottom (RB) flask from your kit and replace it if it is cracked. A flask that has even a small crack may break upon heating. In any distillation, always check the inside of the plastic connectors to see that the ring of plastic in the center is not frayed too badly. If it is, the connection will leak and vapor will be lost. Samples of frayed and good connectors will be on display on the balance bench. Replace frayed connectors with new ones, which are available in the microscale equipment drawers. If you have a question about the condition of the connector, ask your TA. The connector should be checked before every distillation because it may have deteriorated during the previous distillation. To the 5 mL RB flask, add 2.0 mL of dry cyclohexane (fume hood, use a small graduated cylinder), 2.0 mL of dry toluene (fume hood), and a couple of boiling chips. Clamp the neck of the flask securely to a ring stand using a small three-pronged clamp. Using the black plastic connector, attach the distilling head to the RB flask. To the distilling head, attach the thermometer adaptor and thermometer. USE CAUTION when inserting the thermometer into the thermometer adaptor. Hold the thermometer close to the adaptor and push and twist gently. Breakage could result in serious injury. (Note that because mercury poses health problems mercury thermometers are no longer used in this lab.) To further avoid possible leaks, confirm that all glass pieces are seated firmly in the connectors and that the apparatus stands vertically. A common problem is to connect the three-pronged clamp in such a way that stress is
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This note was uploaded on 11/29/2011 for the course CHEM 267 taught by Professor Samal,p during the Fall '08 term at UMass (Amherst).

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distill - Chem 267. Distillation. (rev 7/10). Liquid...

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