Orgo LabC Notes - Laboratory C: Simple and Fractional...

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Laboratory C: Simple and Fractional Distillation Laboratory Techniques: Boiling stones p. 145-146 Heating mantles p. 150-155 Clamps and Clamping p. 156-165 Distillation p. 167-172,180-186 Theory of distillation p. 318-335 Gas Chromatography p. 254-263 Distillation is an incredibly useful technique for purifying compounds. While it has been used for thousands of years, it remains common. Oil refineries carry out massive distillations in which the components of crude oil are separated into many different products. In a distillation, a liquid is vaporized and then recondensed, which allows for the separation of two or more components on the basis of their boiling points. In this lab you will separate a mixture of cyclohexane and toluene by both simple and fractional distillation in order to help you understand the general distillation technique, and to help you better understand whether to use simple or fractional distillation in a given situation. In a fractional distillation, a column is inserted into the apparatus which allows for many more cycles of the liquid being vaporized and recondensed than in a simple distillation. Instead of using a very long column, we will be using a Vigreux column, shown to the left. The Vigreux column has many indentations which allow the vapor to recondense. While fractional distillation leads to better separation of compounds with boiling points relatively close together, it typically takes longer and frequently leads to a lower yield of distilled material. Please note that the book suggests that compounds with boiling point differences of 25 C or greater can be separated by simple distillation. In reality, it is often difficult to separate mixtures with boiling point differences less than 50 C by simple distillation, and fractional distillation is usually the better technique in these cases. This lab is designed to illustrate the difference in the separation obtained in a simple versus fractional distillation. You will distill the SAME 25 cyclohexane/toluene solution using each method so that you can see the difference. mL of We will be using gas chromatography (GC) to analyze the purity of the cyclohexane that we obtain in each distillation. Chromatography is a blanket term for techniques used to separate mixtures of compounds based on partitioning them between a stationary phase and a mobile phase. Chromatography can be used on an analytical scale to determine the identity of compounds in a mixture, and in some cases to determine concentrations of compounds that have been identified. The two instrumental chromatographic techniques are High Performance Liquid Chromatography (HPLC) and Gas Chromatography (GC). Gas chromatography is a very powerful separation technique – under optimal conditions it can resolve compounds with boiling point differences of a few degrees, which is better than any fractional distillation column. Therefore, we will be able to use this technique to determine the success of your separation of cyclohexane and toluene in both your simple and fractional distillations.
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This note was uploaded on 03/24/2009 for the course CHEMISTRY 030.225 taught by Professor Janegreco during the Spring '09 term at Johns Hopkins.

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Orgo LabC Notes - Laboratory C: Simple and Fractional...

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