Separation and Purification
Techniques
Lesson Objectives
At the end of the lesson, students should
be able to:
 Name the 3 methods in which we can
test for pure substances
 Identify the effect of impurities on a
substance.
 Choose suitable separation techniques to
separate a given mixture.
 Explain the working principles behind
each separation technique.
To test for Purity of a Substance
Methods of Testing
Observation
Melting point
If a substance is pure, it will melt
at a fixed temperature.
Boiling point
If a substance is pure, it will boils
at a fixed temperature.
Use of chromatography
If a substance is pure, it will
show only one spot on the
chromatogram.
Effect of impurities in a substance
Attributes
Effect of impurities
Melting point
A substance melts below its
melting point.
Boiling point
A substance boils higher than
its boiling point.
Gives rise to more than one
Use of chromatography
spot on the chromatogram.
Physical Methods of Separation
Only separate the different substances in
a mixture.
 No new substance is formed.

The choice of separation
technique depends on the
nature of the mixture.
Methods based on
physical properties
Particles size
 Solubility

◦ Insoluble/soluble
◦ Degree of solubility
Density
 Magnetic (iron) vs. non-magnetic
 Sublimation (solid  gas)

Techniques…
Decantation
 Filtration
 Sublimation
 Paper chromatography and other types of

chromatography (very powerful method)
Floatation
 Sieving
 Magnetism
 Extraction
 Distillation

Commonly used in
organic chemistry
Filtration
Solid-liquid mixture (insoluble solids) E.g. sand
in water
A filter paper is used because it contains very tiny
pores.

Mixture of solid
and liquid
Applications

NEWater – purification of water using
microfiltration to remove impurities.
Crystallisation

To separate dissolved pure solid from a
Maximum amount
solution.
of solid dissolved
in a given solvent.
2. Saturated solution
Evaporation of solution
3. Pure Crystals formed.
1. Heat the solution
until saturated.
How to test for saturated solution?

Dip a glass rod into the solution and
removed.

If crystals are formed on the glass rod, it
means that the solution is saturated.

This is the saturation point or
crystallisation point.
Mixture of Sand and Sugar

How do I get sand and sugar back?

Filtration  Sand is the residue, filtrate is
the sugar solution

Crystallisation  pure sugar crystals

Is the filtrate always a pure liquid?
Distillation
To separate a liquid from a solution.
E.g. salt solution, sugar solution
 Involves two physical state changes.

Set-up for distillation
1
Bulb of thermometer placed beside
the side arm of the distillation flask to
ensure accurate measurement of
boiling point.
Liquid is heated until
its boiling point and
changes to vapour.
2
Vapour is cooled
and changes to
liquid (distillate).
Mixture
To ensure smooth
boiling.
Other examples:
1. Marble chips
2. Porcelain chips
Main concept
Boiling point of the liquid
Boiling chips
To ensure smooth boiling
 During boiling of water, big air bubbles
can be seen.
 These air bubbles causes ‘bumping’.
 Boiling chips can reduce this ‘bumping’
effect.

How do you separate…
Sand and water
 Alcohol and water
 Corn starch and water
 Iron and sulfur
 Caffeine from coffee beans
 Salt and pepper
 Sand and pepper
