CHE_LAB4(DST)

CHE_LAB4(DST) - Purification by Distillation Techniques...

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Purification by Distillation Techniques Experiment # 4
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Purpose Distillation is a classical process used in the separation of mixtures by vaporization. Vaporization of liquids vary depending on their respective boiling points. The lab focuses on techniques and relative successes of simple distillation aimed at compounds having a boiling point difference of 75 ºC or greater and fractional distillation, a more accurate technique aimed for compounds with relatively similar boiling points. Results and Discussion Simple Distillation 4 ml of 1:1 ratio of cyclohexane and toluene solution was placed in a flask and undergone a simple distillation process. Since cyclohexane and toluene have relatively similar boiling points (81 ºC, 111 ºC) 1 , it was predicted that simple distillation would not yield very effective results in separation of the mixture. Cyclohexane would comprise the majority of the vapor since it has a lower boiling point. However, as the distillation continues, the vapor will soon be comprised of a mixture of both compounds. Thus, the distillate will not be pure. The experimental results for simple distillation are shown below. 1 Williamson, K.L, Minard, R.D., Masters, K.M. Macroscale and Microscale Organic Experiments. Boston, MA, 2007; 91. Simple Distillation 75 80 85 90 95 100 105 0 20 40 60 80 100 Volume (# of drops) Temperature (ºC)
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The first drop of distillate was collected at 77 ºC. This result was not expected since it is below the boiling point of pure cyclohexane. It was expected that the first drop would be above 81ºC since in a liquid mixture, vapor pressure of the mixture has contributions of both compounds. This means that the added toluene will make the solution have a lower vapor pressure as compared to pure cyclohexane making it harder to reach 760 mm hg of pressure to boil. From the graph, it is seen that for about the first 40 drops, the temperature changes very gradually and slightly. It is concluded that the vapor above the solution mostly comprised of cyclohexane since it resembled its boiling point. For drops 50 through 70, we see a sharper increase in temperature. It was assumed that the vapor was changing concentrations at this point. The concentration of cyclohexane is decreasing while toluene is now increasing. By now most of the cyclohexane has been collected in the distillate with some amount of toluene. The fact that the temperature changed about 15 ºC over 20 drops
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This note was uploaded on 05/25/2008 for the course CHE 276 taught by Professor Totah during the Fall '07 term at Syracuse.

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CHE_LAB4(DST) - Purification by Distillation Techniques...

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