2. 3.1 Obtaining Pure Substances from Mixtures
3.2 Separating a Solid from a Liquid
3.3 Separating Solids
3.4 Separating a Liquid (Solvent) from An Aqueous
Solution
3.5 Separating Liquids
3.6 Chromatography
3.7 Determining Purity
Separation and PurificationChapter 3
2
3. Learning Outcome
• describe a method to separate and purify a
solvent from a solution.
At the end of this section, you should be able to:
3.4 Separating a Liquid (Solvent)
from a Solution
3
4. Recall from Chap 4:
Aqeuous Solutions are Mixtures.
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3.4 Separating a Liquid (Solvent)
from a Solution
SOLUTE
5. Simple Distillation
Simple distillation is used to separate a pure
solvent (liquid) from a solution.
Examples:
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3.4 Separating a Liquid (Solvent)
from a Solution
Mixture (Aqueous
Solutions)
Soluble Solid (Solute) Liquid (Solvent)
Sugar solution Sugar (any solute) Water (the solvent)
Aqueous
potassium bromide
Potassium bromide
(Ionic Compound)
Water (the solvent)
6. Setting Up the Distillation Apparatus
Thermometer
bulb should be
just beside the
side arm
leading to the
condenser.
Water enters the
condenser from the
bottom and leaves
from the top.
Condenser must be
sloping downwards.
Boiling chips
are placed in
the flask to
ensure smooth
boiling.
Volatile liquids can be kept in the
liquid state by placing receiver on ice.
water in
water out
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3.4 Separating a Liquid (Solvent)
from a Solution
7. Simple distillation of salt solution
2. Water boils and becomes
vapour. Thermometer measures
temperature of the vapour.
3. Water vapour
is cooled and
condenses into
pure liquid
(distillate).
5. Pure water
is collected
as distillate.
4. The salt solution
becomes more
concentrated as
distillation
continues. Salt will
be collected as
residue.
1. Boiling chips
are added to
ensure smooth
boiling. Water
vaporises, rises
and enters the
condenser. 7
3.4 Separating a Liquid (Solvent)
from a Solution
Editor's Notes
It is an introduction to simple distillation. While we have discussed the methods used to extract the solute from a solvent, how do we recover the other part of the mixture, that is the solvent?
Discuss with students why the above steps are taken.
Why do we take that precaution with the thermometer?
Answer: It registers the boiling point of the liquid we want to collect. That way, we will know when it is distilling over.
2. What would the reading be if the liquid is water?
Answer: 100°C
3.Why do we take that precaution with the condenser?
Answer: This ensures that the condenser is completely filled with water to cool and condense the vapour more effectively. It is sloping downwards to ensure that the distillate flows downwards into the receiver.
This can be carried out in the laboratory as a demonstration using salt (sodium chloride) or coloured water. Students usually will be quite excited to see the distillate coming through as a colourless liquid. Some will volunteer to drink it!
