The document outlines various standard separation techniques for mixtures in chemistry, including methods such as filtration, evaporation, distillation, and chromatography, each with specific applications based on the properties of the constituents involved. It explains the differences between pure and impure substances, as well as the criteria for purity, highlighting that pure substances have consistent melting and boiling points. Additionally, it emphasizes the importance of these techniques in industrial applications and scientific analysis.

1. STANDARD SEPERATION
TECHNIQUES FOR MIXTURES
CHEMISTRY

2. W.A.L.T. – PART 1
• State the different standard methods of
separating mixtures and their individual
applications
• Manipulate different apparatus for separation
techniques
• Draw separation technique apparatus
• State the criteria for purity
• Distinguish between pure and impure
substances

3. • A mixture is a substance formed when
two or more constituents are physically
joined together
• Constituents of mixtures can be
elements, compounds or both
• A mixture does not have a fixed amount
of each element or compound in it
• The constituents maintain their
characteristic properties and can be
separated by physical means
MIXTURES

4. ELEMENTS, MIXTURES &
COMPOUNDS
MIXTURE CONSTITUENTS
Air
Soil
Urine
Palm wine
Milk
Sea Water
Blood
Petroleum
Bronze

5. Attach Classwork
• State five differences between a
compound and a mixture
• State three differences between
homogeneous mixtures and
heterogeneous mixtures
• State three examples each of
the mixtures above
• Note: Use a tabular form to
present your work
ELEMENTS, MIXTURES &
COMPOUNDS

6. SEPARATION TECHNIQUES
• One feature of mixtures is that it is
possible to separate the
individual constituents by physical
means
• Each constituent of a mixture still
retains its individual properties
• There are many different physical
methods used to separate a
variety of mixtures
• Each method is dependent upon
the properties of the constituent
such as solubility, boiling point,
sublimation, rate of diffusion,
magnetic properties etc.
Types of Separating Techniques
include:
1. Sieving
2. Decantation
3. Filtration
4. Evaporation
5. Distillation
6. Fractional Distillation
7. Crystallization
8. Sublimation
9. Precipitation
10. Chromatography
11. Separating funnel method
12. Magnetic Separation

7. TERMS
• Solute
• Solvent
• Solution
Class work
• Describe the following terms
• Give two each examples

8. SIEVING
• This is used to separate solid
particles of different sizes
• The mixture is placed on a sieve
with a mesh of a particular size
• Particles smaller than the mesh
size of the sieve will pass through
the sieve while the bigger
particles will remain on the sieve
• This method is commonly used in
the mining and garri industries in
West Africa

9. SIEVING

10. SIEVING

11. SIEVING

12. MAGNETIC SEPARATION
• This is used to separate magnetic
substances from non magnetic
particles
• It involves the use of a magnet
• A mixture of Iron and Sulphur can
be separated using this method.
The iron is magnetized and the
Sulphur is left behind.
• This method is commonly used in
the steel industry and to remove
magnetic impurities from tin ore.

13. MAGNETIC SEPARATION

14. DECANTATION
• This is a method used to separate a mixture
of liquid and denser solid particles which
separate into two distinct layers on standing
(a process called Sedimentation)
• The upper layer of clear liquid is carefully
poured from the bottom solid portion into
another container
• It is a rapid but inaccurate method of
separation because during separation, the
solid may becomes agitated and may mix
up again with the liquid portion.
• This method is used in the industries for
– The separation of solids from the solution in which they
were cleaned
– To remove whey from the curds when making cheese
– The purification of water
– The cast-decant-cast process to produce alloys of
different composition

15. DECANTATION

16. DECANTATION

17. FILTRATION
• This is a method used to separate insoluble
particles from liquids e.g. sand/dust in water
• It involves the use of a filter paper
• During the process of filtration, the liquid passes
through the filter paper while the solid material
remains on the filter paper
• The liquid which passes through is called the
Filtrate while the portion which remains on the
filter paper is called the Residue
• Filtration gives a better result than decantation
• Used in industries such as
– water purification plants and breweries to remove
impurities from liquids
– In the purification of air prior to liquefying air
– To remove particles from oil e.g. filter pumps in car
engines

18. FILTRATION

19. FILTRATION

20. EVAPORATION
• A method used to separate a
dissolved solute from a solution by
heating the mixture to dryness
• This causes the liquid portion (usually
with a lower vapour pressure) to
evaporate leaving the solid portion
• It works on the principle of different
vapour pressures and the solvent is
sacrificed in the process
• Industrial applications include:
– In obtaining salt from the sea
– In the production of dry milk, starch and sugar

21. EVAPORATION

22. DISTILLATION
• This method is used to recover a solvent
from a solution
• It also a process of
evaporating/vapourising a liquid and
then condensing the vapour
• The vapour passes through a condenser
and is cooled back to a liquid. This
process is called Condensation
• This method can be used to separate
two liquids of different boiling points
e.g. a mixture of ethanol (78°C) and
water (100°C).
• Industrial application: This process is
used to purify liquids and in gin distilleries

23. DISTILLATION

24. FRACTIONAL DISTILLATION
• This method is used to separate a mixture of two or
more liquids with close boiling points into their
component fractions
• This process is similar to distillation, however, a
fractionating column is introduced between the flask
and the condenser
• Separation occurs within the fractionating column as
it is filled with glass beads
• The upper part of the column is at a lower
temperature than the lower portion; therefore
vapours with high boiling points would be
condensed and return into the flask.
• The process is repeated until all components have
been distilled
• Industrial application: this process is used to separate
– a mixture of benzene methyl benzene and
liquefied air into pure nitrogen, oxygen and noble
gases.
– Petroleum into its fractions

25. FRACTIONAL DISTILLATION

26. Class work
• Liquified air is mainly a mixture of
nitrogen and oxygen which can be
separated into its components by
fractional distillation. Boiling points of
nitrogen and oxygen are -196°C and –
185°C.
• Name the fraction which distils over first
• Give reasons for your answer
• Give another industrial application of
fractional distillation as a separation
technique

27. CRYSTALLIZATION
• This method is used to obtain a pure
solid sample from its solution (i.e. it can
be used to separate salts which
decompose easily on heating from
their solutions)
• Salts obtained from this process are
pure and contain water of
crystallization e.g.
– Copper(II) tetraoxosulphate (VI) pentahydrate –
CuSO4.5H2O
– Copper (II) trixonitrate (V) trihydrate –
Cu(NO3)2.3H2O
• Industrial application: it is used in the
manufacture of drugs and sugar
where purity of the product is essential

28. CRYSTALLIZATION

29. SUBLIMATION
• Certain vapours condense to form solids
without becoming liquids
• These solids, when heated are changed
into the gaseous phase without becoming
a liquid. This process is known as
Sublimation
• Examples of substances that sublime
include:
– Ammonium chloride
– Iodine
– Sulphur
– Iron (III) chloride
• These substances can be separated from
other solids via this process
• For example, a mixture of iodine and
sodium chloride can be separated via this
method

30. SUBLIMATION

31. PRECIPITATION
• The process of precipitation involves the
solubilities of solids in different mixable
liquids to precipitate the solid
• This process is carried out by adding a
solvent to an aqueous solution of a
substance
• This method can also be used to separate
two solutes in a solution
• For example: iron (II) tetraoxosulphate (VI)
is soluble in water and insoluble in ethanol;
therefore adding ethanol to an aqueous
solution of Iron (II) tetraoxosulphate (VI)
precipitates the pure solid of Iron (II)
tetraoxosulphate (VI) which can be
separated by filtration and be
recrystallized to get a high degree of purity

32. PRECIPITATION

33. CHROMATOGRAPHY
• This is a technique which can be used to:
– Separate the components in a sample and
thus identify the number of substances in such
sample
– Determine if a substance is pure
• This technique is based on the principle that if a
fluid containing a number of substances is
allowed to pass through an adsorbent medium,
the different substances in the fluid may travel at
different rates and can be separated
• The rate at which each constituent moves is
dependent on the affinity of each constituent for
the solvent and the absorbent medium (i.e.
solutes which are weakly adsorbed by the
adsorbent medium are easily re-dissolved by the
solvent and this travel up the adsorbent quickly).
Also, solutes which are soluble in the solvent travel
up at a faster rate than those which are less
soluble.

34. CHROMATOGRAPHY

35. CHROMATOGRAPHY
• In Paper Chromatography
– The adsorbent medium commonly
used is Filter paper
– Solvents used include ethanol,
methanol, chloroform, ethyl ethanoate
or aqueous phenol
Industrial Application
• Used in medicine to analyze blood or
urine
• Used in the identification of the
components of petroleum

36. SEPARATING FUNNEL METHOD
• This method is used to separate liquids that
are immiscible (i.e. liquids that cannot mix
to form a single liquid) using a filter funnel
with a tap at the bottom
• This method is dependent on the densities
of these liquids
• For example: a mixture of petrol and water
can be separated using this method.
• These liquids separate out into two distinct
layers with the less dense (petrol) on top
and the more dense liquid (water) at the
bottom
• The tap is now opened, the more dense
liquid is run off leaving the less dense liquid
layer in the funnel which can be run off
into another container

37. SEPARATING FUNNEL METHOD

38. FLOATATION
• This method is used to separate two
insoluble solids by mixing them with a
liquid such as water causing one to float
on the liquid and the other to sink
• A mixture of sawdust and sand can be
separated via this method
• Industrial application: it is used to
– Separate a mineral from waste
materials or from other minerals (froth
floatation)

39. FLOATATION

40. CENTRIFUGATION
• Involves the use of a centrifuge. Used to
separate small amounts of a suspension
• Mixtures are placed in a centrifuge which
spins very quickly causing the solid to
move to the bottom
• Liquids can then be decanted from the
tube
• Industrial application: Used in:
– Dairies to separate milk from cream
when producing skimmed milk
– To separate blood cells and plasma

41. CENTRIFUGATION

42. CENTRIFUGATION

43. FROSTATION
• Used to obtain liquids and a concentrated
solute from a solution
• For example, sodium chloride solution is
allowed to cool to a very low temperature in a
freezer
• Pure water freezes out of the mixture in the
form of pure crystals leaving a concentrated
solution of sodium chloride
• This method is used for substances that
decompose when heated
• In industrial applications, it is referred to as
freeze concentration
• In industries:
– It is used to concentrate food products e.g.
juices with delicate flavours
– In waste water treatment to separate
clean water from waste materials

44. CRITERIA FOR PURITY
• Separation techniques are used for the
preparation of substances in a pure state.
• A pure substance is made up of only one
substance and is not mixed with any
other substance
• Impure substances are a mixture of a
pure substance and an impurity. The
presence of an impurity affects the
characteristics of the substances (i.e.
lowers the melting point and raises the
boiling point of a substance)
• Many substances in nature are impure
substances e.g. Air is a mixture of gases

45. PROPERTIES OF A PURE SUBSTANCE
Pure substances will possess the following:
• Sharp melting and boiling points at fixed
temperatures
• A definite density
• Will give one spot on a chromatogram
How can you show if a solid is pure?
• A pure solid will have a sharp and constant
melting point. (i.e. it will completely melt at
a definite or a very narrow range of
temperatures)
• The presence of an impurity in the solid will:
– Lower the melting point
– Cause the solid to melt over a wide
range of temperature

46. PROPERTIES OF A PURE SUBSTANCE
How can you show if a liquid is pure?
• A pure liquid will have a sharp and
constant boiling point. (i.e. it will
completely boil at a definite or a very
narrow range of temperatures)
• The presence of an impurity in the liquid
will:
– Increase the boiling point
– Cause the liquid to boil over a wide
range of temperature

47. DETERMINATION OF THE MELTING POINT OF A SOLID
or TEST FOR PURITY OF A SOLID
• Determination of melting point of a solid
(naphthalene)
– Put some naphthalene in a test tube and
warm the test tube in a bath over a flame. The
solid naphthalene melts and forms liquid
naphthalene
– Put a thermometer into the liquid
naphthalene, turn off the flame and read the
temperature at which the naphthalene
solidifies
– Warm the naphthalene again and read the
temperature at which it melts
– This temperature is the melting point
– Pure naphthalene melts at 80°C
– This process can be repeated after adding an
impurity

48. DETERMINATION OF THE BOILING POINT OF A LIQUID
or TEST FOR PURITY OF A LIQUID
• Determination of melting point of a liquid
(ethanol)
– Put a small quantity of ethanol in a test
tube and heat the test tube in a
beaker of water
– Put a thermometer into the ethanol
– Heat the beaker until the ethanol
begins to boil. As it boils, read the
constant temperature which is the
boiling point of ethanol
– Pure ethanol boils at 78°C