Lab Manual- Experiment 3

Lab Manual- Experiment 3 - 8/26/2010 Experiment 3: SIMPLE...

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8/26/2010 Experiment 3 : S FRACTIONAL DI S TILLATION Reference: Pavia, Techniques 14 and 15, Pages 719-748 INTRODUCTION Distillation can be used as a method for purifying a single liquid and also as a means of separating a liquid from a dissolved solid or from a mixture of miscible liquids. The liquid (or mixture) is heated and, when it boils, the vapors are condensed into a separate receiver. The resultant liquid (distillate) is collected in one or more fractions. A) Purification of a Single Liquid: A single liquid will begin to boil when its vapor pressure is equal to the vapor pressure of the atmosphere. For a pure liquid the boiling temperature should remain constant (within 2 o C) for the duration of the distillation. B) Separation of a mixture: When a solution of 2 miscible liquids is distilled, boiling will begin when the total pressure of the solution is equal to the atmospheric pressure. If the solution is 'ideal' (follows Raoult's Law), the total pressure will be the sum of the partial pressures of each liquid. These partial pressures are dependent upon the vapor pressure of the pure liquid and its mole fraction in the solution. If the boiling points of liquids differ by more than 100 o C, good separation can be obtained by simple distillation, as the partial pressures of the two liquids will be very different. However, if the boiling points are fairly close to each other (say within a 40 o C difference), one cannot obtain sharp separation by simple distillation. A different method must be employed to increase the efficiency of the distillation. This is accomplished by the use of a fractionating column. Our column will consist of a condenser filled with a packing material. C) Fractional Distillation: 1 In order to understand the behavior of two liquids as they are distilled using a fractionating column, you must understand the liquid/vapor composition curves in Pavia on pages 723, 730, 732, 742 and 743. You will have to spend a great deal of time studying Techniques 14 and 15 to understand distillation. Sections 14.2, 14.3, and 15.1-15.6 should be particularly helpful. The column packing provides a surface for these multiple condensation and vaporizations to occur.
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Lab Manual- Experiment 3 - 8/26/2010 Experiment 3: SIMPLE...

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