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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 Daltons Law o P total = Pa + Pb + Raoults 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 mixtures 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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- Spring '08