AQA A Level Chemistry复习笔记4.2.3 Distillation of a Product from a Reaction

REQUIRED PRACTICAL 5

Distillation of an organic product:

• Distillation is a common practical completed in organic chemistry
• For this course, the most common practical in which you will come across distillation and reflux apparatus is the oxidation of primary and secondary alcohol
• This required practical gives you the opportunity to show that:
  • You can use an electric heating mantle rather than a Bunsen burner for heating
  • Use laboratory apparatus for a variety of experimental techniques and can set up glassware successfully
  • Safely and carefully handle different liquids, including those which are corrosive, irritant, flammable and toxic

   

The Distillation Process:

• To  produce an aldehyde from a primary alcohol the reaction mixture must be heated
• The aldehyde product has a lower boiling point than the alcohol ( since it has lost the H-bonding) so it can be distilled off as soon as it forms

Heating under Distillation Apparatus

• The reaction mixture needs to be heated until it boils using a heating mantle
  • Electric heating mantles are used for this because the temperature can be controlled, and because you are using chemicals which are flammable

   

• Quickfit apparatus is then set up, including a pear shaped flask, a still head and a condenser
• A Quickfit thermometer can be used, with the thermometer bulb sitting exactly where the vapours will pass into the condenser
• A steady and constant stream of water passes through the condenser in a 'water jacket' - it enters at the bottom of the condenser and the drainage pipe removes the water from the top of the condenser
• The distillate which forms in the condenser drips directly into a receiving vessel
  • The distillate which should be collected, is that which is given off at +/- 2 oC of the boiling point of the desired product
  • Some distillate may be given off below this temperature - this needs to be discarded and a clean vessel used to collect the desired product
  • Stop collecting the distillate if the temperature rises above +/- 2oC of the boiling point of the desired product