Use of fractional distillation for the purification of mixtures of liquid substances with close boiling points.
Water and acetone are miscible so that the only way to separate them once mixed is by distillation. Fractional distillation is indicated when the difference in the boiling point of the liquids to be separated is approximately less than 20 ºC.
However, although in this case the difference between the e.g. of water and the acetone is greater, this technique will be used because it is very efficient in the separation. The efficiency comes from the incorporation to the assembly of a rectification column that behaves as if multiple single distillations were performed.
In a 250 mL round bottom flask 60 ml of water and 40 ml of acetone are added. In addition, to see clearly at the end of the process the separation of the two colorless liquids, several drops of a dye (bromophenol blue) will be added that will remain in the water and will give it a blue color. One or two boiling chips are also added so that the boiling is homogeneous.
The fractional distillation setup is prepared, using a vigreux column and connecting the water inlets to the water condenser (note that the water inlet is upstream of the condenser). The heating will be carried out gently, so that a progressive and smooth increase of the temperature in the distillation head is observed.
The initial distillate fraction will be collected (in a test tube) at a temperature in the range of 56-62 ºC. The distillate corresponds to practically pure acetone. Approximately one drop of distillate per second is collected in the beaker. When the temperature of 62 ºC is reached or the original amount of 40 ml of acetone is obtained, the distillation process is stopped.
|Compound||Mw||M.p. (ºC)||B.p. (ºC)||D (g·mL-1)||GHS|
International Chemical Identifier
The IUPAC InChI key identifiers for the main compounds used in this experiment are provided to facilitate the nomenclature and formulation of chemical compounds and the search for information on the Internet for these compounds.