ALL of the following techniques (after
this slide) only separate MIXTURES (not
compounds)
– The mixtures are separated based on
differences in physical properties, not
chemical reactions
Separation Techniques
Chemistry 11
Hand Separation /
Mechanical Separation:
Electrolysis could be used to separate
compounds by breaking the bonds in
the molecules
Settling:
mechanical mixture can often be
separated by hand or by the use
of a sieve or magnet.
Uses gravity to pull denser particles
to the bottom of a mixture
•Special Case: Centrifugation
–Uses a machine (centrifuge) to
spin the sample at high speeds
to pull the particles down faster
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Extraction:
1) removing a solid from a
mechanical mixture of solids
Filtration:
Separates solids from liquids or
gases
– Ex. Air filters
The solid which remains behind
on filter paper = residue
The liquid which passes
through filter paper = filtrate
Filtration only works when the
solid particles present are big
enough to be seen
Uses a liquid to dissolve one or more of
the solids present but leaves others
undissolved
Ideally only two solids will be present so
that the desired solid is either
i) Left behind, or
ii) Dissolved and subsequently separated
by simple evaporation of the solvent.
– smaller particles (such as
dissolved salt) simply pass right
through the filter paper
A couple of definitions…
2. Extraction of a dissolved liquid or
solid from a liquid solution
Two liquids are MISCIBLE if they are
mutually soluble in each other in all
proportions
– is immiscible with the solvent already
present
– dissolves one or more desired
substances from the solution and
leaves unwanted substances behind
(or vice versa)
– ie. the liquids mix together
Two liquids are IMMISCIBLE if they
are insoluble in each other (form two
phases)
– ie. The liquids don’t mix together
Note: liquids can be partially miscible
A solvent is added that:
Two solvent layers form and are
separated using a separatory
funnel
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Distillation:
Uses differences in boiling point to separate two
or more liquids
The liquids are heated
– Liquid with lowest boiling point evaporates first
– This vapour is cooled and collected and called the
distillate
This process gives good results as long as the
boiling points of the liquids are not too close
together
Recrystallization:
Evaporation:
separates solids or dissolved solids from
liquid by removing the liquid
– Can wait for the liquid to evaporate or boil
it off
used to purify solids
– Dissolve solid in minimum hot solvent possible
– Cool down the solution or evaporate off the
solvent slowly to cause the solid to reform
without the impurities in the solid that were
present before
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Paper Chromatography:
Chromatography:
Used to separate multiple dissolved solids
from a liquid solution
Multiple types
– We will look at paper chromatography as our
example
3 components:
– Mobile phase (developing solution)
– Stationary phase (paper)
– Analyte (chemicals being analyzed)
analyte (dissolved solids) are put on the chromatography
paper at a marked location
Paper is put into a developing solution (a solvent that
will carry the analyte up the paper)
The different solids interact with the paper differently
– The solids that interact strongly are harder to move up the
paper and are separated out first
– Weaker interacting solids travel farther up the paper
After some time passes, the paper is removed
from the developing solution and the “solvent
front” is marked
– “Solvent front” is the farthest point the solvent
moved to
By analyzing how far the dissolved solids
traveled compared to how far the solvent
front moved (as well as other properties) the
solids can sometimes be identified
Rf = distance substance traveled
distance solvent front traveled
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