Unit 6 C2: Separation Techniques
You will learn about:
• Pure substances
• Methods of purification:
- Chromatography
- Filtration
- Crystallization
- Distillation
How do we know which are the real products?
Testing for Purity
Pure Substances
Composition
Mixtures
A single substance
Contains two or
not mixed with
more substances
anything else
Melting and
boiling points
Fixed points
Over a range of
temperature
Chromatography
Produces a single
spot on the
chromatography
paper.
Contain two or
more spots.
(i) Chromatography
1
 A technique using a
solvent to separate a
mixture into its
components.
 E.g separate dyes in ink,
detect traces of banned
food substances, identify
poisons or drugs.
Procedure:
1. Food colouring is applied to
chromatography paper.
2. The paper is dipped into a solvent.
(e.g water, alcohol)
3. The solvent travels up the paper,
dissolving and carrying the dye along
with it.
4. Coloured spots are seen in different
positions on the paper at the end of
results.
Culprit
Ben Johnson
stripped
from his
Olympic gold
in 1988.
ii) Filtration: separating a solid from liquid
1. A mixture is poured into the filter funnel
lined with filter paper.
2. Liquid particles are small enough to go
through the pores of the filter paper but
the solid particles are too large to go
through.
3. Collect the filtrate that passes through
the filter paper in a conical flask. The
solid that remains in the filter paper is
called residue.
iii) Evaporation to Dryness &
Crystallisation
Procedure:
1. Pour some distilled water into the
mixture to dissolve the soluble
substance.
2. Filter the mixture.
3. Wash the residue with a little
distilled water to remove all the salt
solution from it. The residue is sand.
4. Evaporate the filtrate to dryness.
Salt is recovered.
iv) Distillation: separating a liquid from a
solution
Procedure:
1. Solution is heated in a flask until
the solution boils.
2. Pure liquid turns into a vapour and
leaves the flask
3. Vapour is then cooled by a
condenser, which changes it back
into a liquid
4. Liquid is called the distillate and is
collected in a conical flask.
How does simple distillation work?
2. In the condenser, water
vapour condenses.
3. Pure
water is
collected as
distillate.
1. In the distillation flask,
water boils and enters
the condenser.
SAFETY MEASUREMENTS:
Thermometer
This ensures that the
thermometer measures the boiling
point of the substance that is
being distilled.
Boiling
Chips
To ensure smooth boiling.
If the distillate is volatile, the
receiver can be put in a large
container filled with ice.
This helps to keep the
temperature of the distillate low
so that it remains in the liquid
state.
Eg. Finding out the dyes present in
sweets
Paper chromatography
• a method of
separating &
identifying mixtures.
• a suitable solvent is
used.
Purity of Substances
• pure substances have fixed melting
and boiling points
• melting points and boiling points are
changed by the presence of
impurities