Fractional Distillation Organic Lab Report

Topics: Distillation, Boiling point, Theoretical plate Pages: 8 (2938 words) Published: April 23, 2013
Organic Lab 1: Fractional Distillation
With the purpose of the experiment being to identify the 30 mL of unknown liquid, the theoretical basis of simple and fractional distillation must be deconstructed and applied to the data obtained describing the liquid in question. Simple distillation is a separation technique which can be used to separate and purify distillates from a liquid mixture which ideally contains one volatile and one non-volatile compound. If such ideal conditions are not possible—as is usually the case—then simple distillation can be applied as long as the liquid in question is composed of compounds that differ in volatility such that their boiling points differ by at least 40 to 50 degrees Celsius. Because the very essence of simple distillation is relies upon the idea that more volatile compounds have lower boiling points and thus when heated to this boiling point will occupy most if not all of the vapor above the liquid pot residue. Because the difference in boiling point for the compounds in a mixed liquid must at least differ by 40 to 50 degrees Celsius in order for purification through Simple Distillation, this procedure should not result in a high amount of impurities in the distillate or pot residue since the difference between both boiling points is great enough that most of the lower boiling point liquid should vaporize without vaporization of the higher boiling point liquid. The experimental set up for the simple distillation procedure is the standard procedure which invokes the use of a a heat source, a magnetic stirrer, a receiving flask for the distillate to be collected in, a condenser with an accompanying inflow of cold water, a stillhead, a thermometer, a rubber adapter, an adapter, and keck clips. The keck clips are used to stabilize the glass joints while the condenser cools the vaporized gas to liquid. Because the stillhead is where the vapor collects, and the thermometer attached to the top of the stillhead must record the temperature of the vapor—and thus boiling point of the distillate—the bottom of the mercury bulb of the thermometer must be directly adjacent to the bottom of the opening of the arm of the stillhead. When distilling a stir bar must also be used in order to disturb the heat evenly throughout the solution. The apparatus must be loosely covered in cotton and aluminum foil, such that the apparatus is transformed into an isolated system from the environment that does not receive nor release the added heat into the surroundings. This ensures that all of the added heat and temperature change results from boiling point properties of the compounds in the solution. Fractional distillation, like simple distillation is also a separation technique that takes advantage of the differing boiling points of two compounds in a liquid. This technique however, differs from simple distillation in the sense that it can be applied to differences in boiling points of two compounds more sensitive than 40 to 50 degrees Celsius, i.e. 20 to 30 degree Celsius of a difference. This implies that while the lower boiling point liquid occupies most if not all of the vapor at its respective boiling point, in fractional distillation this vapor is composed of the vaporized lower boiling point compound as well as a significant amount of the higher boiling point liquid. In fact, if simple distillation were to be used to separate a binary mixture when fractional distillation was in fact the appropriate technique to be applied, such a distillation would yield an impure distillate. This character would be self-evident in the temperature against volume graph of such an inappropriately applied simple distillation as the temperature would steadily increase and eventually level off only once, indicating that the distillate collected was no more special than the condensed liquid that could be collected from simply heating a compound and then cooling it although the distillate obtained would be more...
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