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Unformatted text preview: Orgo Lab Theory Quiz #1 Simple Distillation Lab Distillation: the process of heating a compound to its boiling point, capturing and cooling the resulting hot vapor, and finally collecting the condensed liquid in a separate receiver Uses of distillation Because each pure liquid has a characteristic boiling point, distillation can be used to: • Identify • Separate and/or purify compounds from mixtures Clicker Question: Why does it take longer to boil an egg in Colorado than on Long Island? • The boiling point of water is lower at high altitudes Boiling point: the temperature at which the vapor pressure of a pure liquid equals the external pressure on the surface of the liquid, is the boiling point at that pressure • The external pressure is usually the atmospheric pressure (760 mmHg) o Boiling points depend upon pressure • The boiling point at atmospheric pressure is called the normal boiling point • Lowering the pressure lowers the boiling point (vacuum distillation) • P System = P A standard Boiling Points of mixtures • Dalton’s Law o P total = Pa + Pb +… • Raoult’s Law o Pa = (P a; vapor pressure of pure A)(Mole fraction A) o Pb = (P b; vapor pressure of pure B) (Mole fraction B) • The higher the Pressure of pure A the higher the mole fraction of A at the mixture’s boiling point • P a > P b ---> X a > X b in distillate • Pure A is not obtained unless there is a large difference in boiling points o Perhaps BP a- BP b > 100 degrees C o One can redistill and improve the separation Boiling Point Determination • Boiling point is measure during distillation • Temperature of the vapor is measured • The liquid may be contaminated or superheated Azeotropes: Non-ideal mixtures of liquids • An azeotrope is a homogeneous vapor with constant boiling point • In an azeotrope, the components of the mixture interact strongly with one another, changing the behavior of each • Azeotropes can be positive (lower boiling than any of the components) or negative (higher boiling than any of the components) Experiment • Do not let the thermometer touch the glass wall of the distillation apparatus...
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This note was uploaded on 01/18/2011 for the course CHEM 132 taught by Professor Laceyandhanson during the Spring '08 term at SUNY Stony Brook.
- Spring '08