Separation of mixtures
Substances are mixed physically in a mixture
Element is a pure substance made up of
only one kind of atoms. E.g. Sodium,
Hydrogen, carbon
 Compound is a pure substance made up
of two or more elements combined
chemically. E.g. water, alcohol, carbon
dioxide, copper sulphate
 Mixture is an impure substance consists of
two or more substances mixed physically.
E.g. Air, mud water, petrol, milk
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Magnetic separation
If one of the substances in the mixture
is magnetic, we can separate it by using
a powerful magnet.
Eg: iron from a mixture of iron and
sulphur
Filtration
If the solid does not dissolve in the
solvent, we can filter the solid out by
filtration
 Chalk powder from a mixture of chalk
powder and water
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Decantation
 A method to separate an insoluble solid
from a mixture
Eg: Mud from a mixture of mud and
water
Separating funnel
If two liquids are immiscible, they can
be separated by using a separating
funnel
Eg. Oil and Water
Evaporation
 If a solute is completely soluble in a
solvent, evaporate the solvent to get the
solute. (make sure that the solute does
change on heating)
 Evaporation is done in an evaporating dish.
Eg: salt from salt solution.
Crystallisation
If the solute is dissolved in a solvent, we can get
the pure solute by this method.
 Sometimes the solute decomposes or evaporates
water of crystallisation on complete drying.
 A saturated solution is heated until point of
crystallisation and then cooled.
 Crystals will be formed at the walls of the
container.
Eg: Copper sulphate from copper sulphate solution.
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Centrifugation
This method is useful to separate a solid in a
suspension
The solid particles settle at the bottom of the test tube
when it spins
Sublimation
 Substances changes to gaseous state without
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passing through a liquid state is called
sublimation.
If substance which slows sublimation is
present in a mixture, we can separate it by
this method.
Eg: Iodine from a mixture of iodine and sand
Distillation
This method is useful to separate a solvent
from a solution.
 A condenser is used in simple distillation
 Eg: Water from salt solution
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Fractional distillation
 This method is used to separate two
miscible liquids from their mixture.
 Fractional distillation is done based on
Boiling Points.
 Eg: Alcohol and water from their
mixture
Chromatography
This method of separation is used to see
what coloured materials make up e.g. a
food dye analysis.
 The material to be separated e.g. a food
dye (6) is dissolved in a solvent and
carefully spotted onto chromatography
paper. Allow a suitable solvent to run
 Alongside it are spotted known colours
on a 'start line' (1-5).
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In chromatography there is a stationary
phase and a mobile phase.
Mobile phase takes different components
to different parts of the stationary phase.
The distance travelled by the components
depends on the solubility of the
component.
If the component is white, it is not
visible. Then spray a chemical(like
ninhydrin) over the paper so that the
component will be visible.
Such chemicals used to make the
components are called locating agents.
Chromatography can be used
to identify the components in
a mixture too.
 Put several drops of the
mixture on the base line. Put
drops of suspected
components also on the line.
 Run the solvent.
 See the components ran equal
to the suspected ones.
 In the chromatography on the
right side, mixture M contains
B, C, and D and not A
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Another way to identify the components in a
mixture is by calculating Rf values.
Each substance has a definite Rf value which
you can find in reference sources.
Conduct the chromatography and calculate the
Rf value for each component by the following
method:
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Rf= Distance travelled by the component
Distance travelled by the solvent front
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Compare the Rf value calculated with that of
book value and identify the components.
Look at the
chromatograph on
right hand side.
 Mixture M contains
components A and B
 Rf of A = 4.30 =0.26
16.80
 Rf of B = 10.20 =0.61
16.80
 Find which substances
have the calculated Rf.
 It means M contains
these components.
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THE END