Distillation…

Words you should know…

• solution – a mixture of one or more substances dissolved in another
• solvent – the liquid in which something is dissolved
• solute – the substance dissolved in a solution
• soluble – able to dissolve (in a particular solvent)
• insoluble – not able to dissolve (in a specific solvent)
• concentrated – the more solute dissolved, the more concentrated the solution is said to be
• dilute – a very watered down solution
• saturated – a solution in which the greatest mass of solute is dissolved in a particular volume of solvent (at a given temperature)
• Liebig condenser – a glass tube with a water-cooled outer jacket to condense vapour back into liquid
• pure – containing only one type of molecule (e.g. pure water contains only water molecules, pure table salt is only sodium chloride & pure argon has only argon atoms)

To extract a pure sample of the solvent from a solution, distillation is used. The mixture is heated until the solvent, which has a lower boiling point than the solute, evaporates. The vapour rises up through the apparatus until it can be cooled back down into a liquid. The liquid collected during distillation is called the distillate. You can do it simply by collecting the distillate in a test-tube that is cooled with a container of iced water. This works well but you do lose a lot of vapour before it has a chance to condense.

A Liebig condenser is constantly cooled by cold water passing through its water jacket. It does not allow a significant quantity of vapour to escape. Notice that it is not connected at the collection end – there has to be a route for the hot expanding air to leave.

You can read more about separating mixtures on the blog by clicking the following…

Separating mixtures

Questions…

1. In the diagrams above, how must the air-hole on the Bunsen burners be set?
2. How would you separate a mixture of…
   • (a) sand from water
   • (b) salt from water
   • (c) iron filings from copper turnings
   • (d) salt from sand
   • (e) water from copper sulfate solution
3. In a cup of instant coffee, what is the solvent?
4. Why is the idea of ‘pure air’ at odds with the passage above?
5. What slightly different technique would you use to separate a mixture of ethanol dissolved in water?