Distillation - Distillation Distillation is a physical...

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Distillation Distillation is a physical separations technique based on differences in component volatilities within a mixture. We will utilize it in two ways this semester: to separate/isolate two volatile and miscible liquids (Exp #2) to isolate a volatile liquid from a nonvolatile, but soluble solid (Exp #3) This technique is characterized by a cycle of liquid vaporizations and condensations. Generally, a solution is heated to boiling, the resulting vapor is isolated, cooled (condensed), and then collected in a receiving flask. The collected liquid is termed the distillate ” and is typically pure if the distillation is performed correctly. Distillation is based on physical properties with which you are already familiar from general chemistry, but that will be reiterated for the sake of clarity. As a liquid is heated, it establishes an equilibrium between liquid and gas phases. As the temperature of the liquid rises, the number of molecules entering the gas phase increases. The gas phase molecules exert a measurable pressure above the liquid which is termed the vapor pressure. This value varies with temperature and as the temperature rises, so does the vapor pressure. The temperature at which the vapor pressure equals the environmental pressure above the liquid is defined as the boiling point. When working with a pure liquid, these values are dependent upon the temperature of the boiling flask, the applied external pressure and the identity/volatility of the liquid. As we begin distilling more complex solutions (two or more miscible liquids), we must subtly redefine vapor pressure and vapor composition in order to fully understand how a mixture behaves at high temperature. For mixtures of miscible liquids , Dalton’s law of partial pressures is used to define the composition of the solution vapor. Dalton s law states that, at a given temperature, the total vapor pressure of a solution (P T ) is the summation of the partial vapor pressures of each of the components present in the mixture (P A , P B , P C ). This can be expressed as P T = P A + P B + P C. How
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This note was uploaded on 01/29/2012 for the course CHEM 234-54 taught by Professor Morrison during the Fall '09 term at UGA.

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Distillation - Distillation Distillation is a physical...

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