lab 3 - Separation of Liquids by Simple Distillation Mayank...

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Separation of Liquids by Simple Distillation Mayank Kumar February 23, 2007 Methods and Background The purpose of the experiment was to separate ethyl acetate and butyl acetate by simple distillation and determine the separation efficiency by construction of a volume (of distillate) versus temperature graph and analysis of the distillates through gas chromatography. Given a system with a liquid in a container, the rate at which molecules in the gas phase reenter the liquid will eventually become equal to the rate at which they escape from the liquid, resulting in a dynamic equilibrium. The molecules in the gas phase will collide with the walls of the container, producing pressure referred to as the equilibrium vapor pressure, which varies directly with temperature. When the equilibrium vapor pressure equals the atmospheric pressure (760 Torr or 1 atm), the rate of evaporation of the liquid increases significantly and bubbles form; thus it has reached its boiling point. When considering mixtures of liquids, Raoult’s law is used to determine the partial pressure of each liquid, as it states that the partial pressure is equal to the product of the equilibrium vapor pressure and the mole fraction. Dalton’s law of partial pressures then dictates that the partial pressures of the liquids must sum up to the total pressure of the liquid. Boiling points are affected by intermolecular forces; molecules with greater attractive forces have higher boiling points because it takes more energy to break the bonds between the molecules. Although ethyl acetate (EtOAc) and butyl acetate (BuOAc) have similar polarities due to the presence of ester functional groups, butyl acetate is a larger, more massive molecule, thus the Van der Waals forces between its molecules will be greater, leading to stronger intermolecular bonds and a higher temperature required to cause butyl acetate to boil (boiling point). Ethyl Acetate (EtOAc) Butyl Acetate (BuOAc) Source: http://membres.lycos.fr/leflacon/img/ Simple distillation separates distillates from less-volatile substances by first vaporizing liquids through boiling and then condensing them. It is specifically used when separating liquids that differ in boiling points by more than 40-50 °C. Since the more volatile liquid in a mixture has a higher equilibrium vapor pressure and thus a higher partial pressure, the vapor of the mixture of liquids contains a greater proportion of the components of the more volatile liquid. As the vapor
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condenses, it should yield a liquid that has a higher concentration of the more volatile component, thus separating it from the less-volatile components. Gas chromatography (GC) is used to separate mixtures of volatile compounds when their boiling points may differ by less than 0.5 °C. The sample is vaporized and moved by the carrier gas (mobile phase) through a column of thinly divided solid coated with a thick liquid possessing a high boiling point (stationary phase). The components that are more attracted to the mobile
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lab 3 - Separation of Liquids by Simple Distillation Mayank...

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