PRIVATE ISTEK ACIBADEM HIGH SCHOOL
2011-2012 9th GRADE CHEMISTRY COURSE
SEPARATION METHODS (1)
Mixtures are composed of more than one type of atom that have just been physically mixed
together but not chemically combined. Mixtures can be separated back into their components by
physical methods (different separation methods)
In general, a mixture can be separated into its components by making use of the difference in
physical properties of the components of the mixture.
Different Methods to Separate Mixtures:
1- Picking Up (based on grain size):
In heterogenous solid-solid mixtures, if the grain size or shapes of components are big
enough,
then the different size grains in a mixture are picked up by using forceps.
2-Sieving (based on grain size) :,
In heterogenous solid-solid mixtures (a
mixture of various-sized particles finer
and larger particles such as table salt
and red pepper), either dry or
suspended in a liquid, are separated
into two or more portions, by passing
through screens of specified mesh sizes.
3-Filtration (based on grain size):
When the mixture contains a liquid
and a solid component, then we filter the
liquid component out. To separate an
insoluble solid from a liquid. The solid
remains in the filter paper and the liquid
goes through the paper into the beaker.
This method is used to separate the solid
from a liquid through a filter paper.
The solid particles of remaining on the
filter paper are called the ‘residue’ and the
clear liquid collected in the container is
known as the ‘filtrate’.
A-Filteration plays an important role both in industry and in our daily lives.
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i-To purify water, they pass it through layers of gravel, sand and coal dust.
ii-Oil filers in cars filter out small pieces of metal pieces formed in engine when it’s on.
B-Filteration is also used for separation of solid-gas mixtures .
i.
ii.
Dust and smoke in polluted air can be filtered out by means of air filters.
In factories, gas filters are used to separate solid particles from vapour coming out of
factory chimneys.
iii. Air filters in cars filter out dust and large particles in air.
iv. Also, to filter out poisonous gases produced due to fires, due to biological or chemical
weapons, gas masks are used.
4- Centrifuges and Centrifuging (based on grain size) :
Centrifuges are devices that can be used to separate insoluble materials from a liquid,
where normal filtration does not work well (e.g. a suspension of very tiny solid particles.)
The mechanism depends on spinning. When rotation of the centrifuge stops, the solid particles
end up at the 'bottom' of the glass tubes with the liquid above. After the centrifuging operation,
the liquid can be decanted off and the solid is left at the bottom of the glass tube.
The centrifuge can be used for:
i- Edible oils, wines and spirits can be cleaned or 'clarified' of solid impurities.
ii- Expensive oils and other fluids used as lubricants in machining metal parts in industry become
contaminated with tiny metal fragments.
5- Dialysis (based on grain size) :
Dialysis, a technique frequently used in biochemistry, is a membrane-separation method
used for removing dissolved salts from solutions of proteins or other large molecules.
This method is an effective means of concentrating impurities, recovering
contaminated solvents, cleaning up polluted streams, and desalinizing
seawater, purification of blood in dialysis machines, separation of pollutants
from drinking water.
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6-Precipitation (separation by density difference):
The formation of a solid in a solution
during a chemical reaction. When the reaction
occurs, the solid formed is called the
precipitate, and the liquid remaining above
the solid is called the supernate.Solids are
then separated by filtration or floatation .
Remember : Pb(NO3)2(aq) + KI(aq) → PbI2(s) + KNO3(aq) ; PbI2(s) is a yellow precipitate.
7-Decantation ( separation by density difference):
Decanting is the simplest possible way of separating a liquid from an insoluble solid which
has a density greater than water. The solid-liquid mixture is allowed to stand e.g. in a beaker, until
all the solid settles out to the bottom of the container.(It involves keeping the liquid aside for
some time and waiting for the heavy particles to settle down at the bottom of the container. This
is called Sedimentation.)
After this, the liquid may be poured into another container without disturbing the settled
particles (to leave the insoluble solid behind). This transfer of liquid is called “Decantation”.
Examples: Wine may be served in a decanter to leave the undesirable solids behind – however,bits
of cork might float!
8-Floatation( separation by density difference) :
Solid substances can be separated by making use of difference in their densities. Dense
components sink, and lighter ones float. This method is applied to heterogeneous mixture with
phases with different densities.
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9-Electrification :
Some substances are attracted by electrically charged objects.
 Do you remember how your hair stands out as you comb it ?
 Do you remember how a plastic rod rubbed against a piece of cloth will pick up small
pieces of paper ?
10- Separation by magnetIc properties :
This can be used to separate iron from a mixture with sulphur. It is used in recycling to recover
iron and steel from domestic waster i.e. the 'rubbish' is on a conveyer belt that passes a powerful
magnet which pluck's out magnetic materials.
 Remember how you can separate Iron-sulfur mixture by means of a magnet?
11-Evaporation :
This is good for separating a soluble solid from a
liquid (a soluble substance dissolves in water to
form a solution). For example, copper sulphate
crystals can be separated from copper sulphate
solution using evaporation. Remember that it is
the water that evaporates away, not the solution.
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