Chem 333L Experiment 2a/b: Simple Distillation and Fractional Distillation Objectives 1. Set up apparatuses for both simple and fractional distillation. 2. Carry out a simple distillation of an unknown. 3. Identify unknown from the boiling point. 4. Perform fractional distillation of a 1:1 solution of cyclohexene and n-butyl acetate. 5. Collect a sample of each distillate and determine the identity of each using IR spectroscopy. Intro/Theory Distillation: Distillation is the best method for determining boiling point if enough material is obtained. Distillation is done by heating a solution to boiling and condensing the vapors. 1. Properties of liquids: Liquids, like solids, are held together by intermolecular forces. There is a lower amount of attractions, allowing for a higher fluidity. When the forces are overcome, the liquid will vaporize. a) Vapor Pressure The vapor pressure is the pressure exerted on the atmosphere above it. Boiling occurs when this pressure equals or exceeds the atmosphere's presure on the liquid. b) Boiling Point 1. The boiling point of a liquid is the temperature at which the energy in the form of heat is sufficient to raise the vapor pressure of the liquid equal to or beyond the atmosphere pressure. 2. The boiling point can be used to characterize compounds. 3. Determining the boiling point is more than simply recording it. Distillation is a less effective indicator because it requires more material and is less affected by impurities. 4. Impurities can either lower or raise the boiling point of a liquid depending with the compound. 5. Pure liquids have constant boiling points so any change during distillation is an indicator of impurities. 2. Factors that cause variations in the boiling points of liquids: a) Internal factors 1. Molecular weight i. Boiling point increases with molecular weight. ii. 162 C for methane to 330 C for n-C19H40 (normal saturated hydrocarbons). iii. Lower molecular weight to higher. 2. Polarity i. Same molecular weight molecules will have higher boiling points ii. Molecules that can form H-bonds will boil higher 3. Shape i. A spherical molecule has a lower boiling point due to decreased ability to attract other molecules. Less attractions will lower the boiling point. b) External Factors 1. Applied Pressure (usually atmospheric) on the liquid i. Boiling point is a function of atmospheric pressure. ii. Boiling point of most liquids decreases about 0.5 C for each 10 mmHg decrease in applied pressure. 2. Added solute i. Will raise the boiling point because it interferes with vapor pressure. Simple Distillation is only useful to separate two liquids with vastly different boiling points (at least 20 C). A flask containing with mixture is heated to boiling The liquid with the lower boiling point will boil first, thus forming themajority of the vapor. The vapors are then condensed and collected into a separate vessel. As a result, the two liquids will be mostly separated into two vessels. The liquids are not 100% pure without another distillation. 3. General Points to Include a) Barometric Pressure: Most distillations are done in an open system to the air, which means that the boiling point can be affected by barometric changes. Barometric pressure is important to note during the experiment. b) Viscosity: The resistance of a fluid to flow. c) Azeotropes: A mixture of liquids of a certain definite composition that distills at a constant temperature without change in composition. Azeotropes have a constant boiling points that are neither below or above the boiling points of the individual components. Fractional Distillation The combination of multiple simple distillations at one time by using a fractional column. The column is connected to the top of the flask that contains the mixture. The original flask is then heated until boiling begins. Again, the liquid with the lower boiling point will vaporize first. The vapors will rise up into the fractional column and condense in the column. As more vapors move up in the column, they will heat the condensed liquid in the column, causing them to return to vapor move further up. Each time a liquid goes to the vapor phase and back to liquid, this is a complete simple distillation and known as a theoretical plate. The greater the number of theoretical plates, the purer the isolated compounds will be. 1. Fractionating Column The height of a fractionating column allows the temperature to vary along the tube. This allows for multiple distillations to occur before the final product is attained. At each simple distillation in the column, a theoretical plate is formed and the mixture becomes more pure. The height of the column controls the amount of theoretical plates before the final product is formed. The time of the experiment and the surface area of the interior of the column can also affect it. 2. Types of Fractionating Columns There are many types, of these is the Vigreux column which will be used in this experiment. This type contains branches stemming from the inner wall. Other columns include many levels of trays or small beads filling th einterior of the column. 3. Other types of distillations 1. Vacuum Distillation-This method is different from both simple and fractional distillation in that it lowers atmospheric pressure to meet the vapor pressure of the liquid being distilled, rather than raising the vapor pressure to meet it. 1. It does not require heat 2. Useful in distilling liquids with extremely high boiling points or when the liquid cannot be heated. 3. Occasionally used in addition to fractional distillation. 2. Micro Boiling Point Determination This method determines the boiling point of a liquid that is small in quantity. It involves the use of Thiele Tube or a large test tube filled with a mineral oil and heated around the sample. When vapor pressure equals the atmospheric pressure, the liquid you are boiling will begin to rise up the capillary tube. Simple distillation gives more accurate results, but requires more material than this method. MechanismProcedure Experiment 2a: Simple Distillation 1. Place 15mL of unknown in a dry, 25 mL round bottom flask with a boiling chip. 2. Set up a simple distillation apparatus. Sink the round bottom flask in the heating mantle insuring that there is sand beneath the flask but also surrounding the flask. This will distribute