Separating Mixtures: Techniques and Everyday Applications

Mixtures and their separations
Janadi Gonzalez-Lord

2

Prepared by JGL 8/9/2009

Table of contents
• Syllabus requirements
• Pure and impure substances
• Classification of mixtures
• Separation of mixtures
• Types of separation techniques
• Experiments
• Industrial uses
• Separating mixtures in everyday life

4


Syllabus requirements - Mixtures
a) differentiate between mixtures and compounds in terms of composition and formation

b) recognize that the components of mixtures can be separated by simple means

c) define the terms : miscible , immiscible , soluble , insoluble , heterogeneous , homogenous , and
apply them correctly i.e. miscible refers to liquids , soluble to gases and solids

d) identify mixtures as solutions , suspensions , colloids , emulsions based on the states of matter
present and their solubility / miscibility

e) define solute and solvent

f) identify dissolving as one substance fitting in between the spaces of another substance .

g) identify a method of separating mixtures based on their composition

h) describe the separating methods of simple distillation , fractional distillation , filtration , layer
separation

i) draw line diagrams for the methods in (h)

5


Syllabus requirements - Mixtures
j. carry out filtration and layer separation in the laboratory and write up notes about the
procedure and results

k. recognize that filtration separates particle based on size

l. Identify sieving , sifting and straining as everyday methods of filtration

m. observe the set up as a teacher demonstration the simple distillation process

n. identify other methods of separation such as chromatography , centrifugation , solvent extraction

o. suggest methods for separating mixtures based on the properties of their components e.g. sand
and salt

p. name two industrial methods of separating mixtures e.g. fractional distillation used to obtained
distilled spirits , centrifugation used to separate components of blood / body fluids in laboratory
testing , filtration in purification of domestic water supply

7


Matter can be sub-divided into PURE and IMPURE SUBSTANCES or MIXTURES.

PURE substances can be sub-divided into ELEMENTS and COMPOUNDS

IMPURE substances or MIXTURES can be sub-divided into HOMOGENOUS and
HETEROGENOUS

8


Can be separated into

Can be
Can be separated
separated into
into

Source: www.mghs.sa.edu.au/Internet/Faculties/Science/Year10/Pics/elementsAndCompounds.gif

9


Elements versus compounds
An element.... A compound......
• consists of only one kind of • consists of atoms of two or
atom more different elements
• cannot be broken down into a bound together,
simpler type of matter by • can be broken down into a
either physical or chemical simpler type of matter
means (elements) by chemical means
• can exist as either atoms (e.g. (but not by physical means),
argon) or molecules • has properties that are
(e.g., nitrogen). different from its component
elements,
• always contains the same ratio
of its component atoms

10


An element
Consists of only one kind of atom
Ar
Ar
can exist as either atoms (e.g. argon)

or molecules (e.g., nitrogen).

cannot be broken down into a simpler
type of matter by either physical or
chemical means

N N If you try to break apart an atom or
molecule, you get an ATOMIC BOMB

N N

11


H H A compound
O consists of atoms of two or more
different elements bound together

always contains the same ratio of its
component atoms
H H
O Water (formula H2O)

For every water molecule, there are 2
Hydrogen atoms for every 1 Oxygen
H H O O H H atom
O
has properties that are different from its
H H component elements
O
For example, hydrogen and oxygen are
gases but water is a liquid
H H
O

12


Examples of elements and compounds

Elements

Compounds

Source: www.physicalgeography.net/fundamentals/images/compounds_molecules.jpg

13


Compounds versus Mixtures
A mixture.... Remember that a compound...
• consists of two or more • consists of atoms of two or
different elements and/or more different elements
compounds physically bound together,
intermingled • can be broken down into a
• can be separated into its simpler type of matter
components by physical (elements) by chemical means
means, and (but not by physical means),
• often retains many of the • has properties that are
properties of its components. different from its component
Syllabus requirement met: elements,
differentiate between mixtures and • always contains the same ratio
compounds in terms of composition and of its component atoms
formation

14


A mixture can be...
A mixture of different
A mixture of different A mixture of different
types of atoms and
types of atoms types of molecules
molecules

N N
N N

O O

H H
H H

Cl H

15


Match the following
1. Pure elements Answer: A, C, D

2. Elements made of SINGLE ATOMS
Answer: A, D
3. An element made of MOLECULES
Answer: C
4. Mixture of TWO elements
Answer: E, F
5. Mixture of THREE elements
Answer: H
6. Pure compounds Answer: G

7. Mixture of TWO compounds
Answer: B

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17


Mixtures can be......
Homogeneous Heterogeneous
• The prefixes "homo"- indicate • The prefixes: "hetero"-
sameness indicate difference.

• A homogeneous mixture has • A heterogeneous mixture
the same uniform appearance consists of visibly different
and composition throughout. substances or phases.

• Many homogeneous mixtures • The three phases or states of
are commonly referred to as matter are gas, liquid, and
solutions. solid.
Syllabus requirements met:
define the terms : heterogeneous , homogenous and apply them correctly

18


Example of homogeneous
mixtures
Some mixtures around us are things we
don't even think of as mixtures.

Vinegar is a homogeneous mixture of
water and acetic acid (CH3COOH).

Most commercial vinegars have an
acetic acid content of about 5%. Acetic
acid gives vinegar its characteristic odor.

19


Example of heterogeneous
mixtures
The combination of oil and vinegar in
salad dressing is a common example of a
HETEROGENEOUS mixture.

Here the two layers are distinctly visible.

Each layer by itself is considered a
HOMOGENEOUS mixture.

20


Mixtures can be same phase.....

Liquid +
Liquid
Solid + Gas +
Solid Gas

Mixtures

21


Or Mixtures can be mixed-phase

Solid +
Gas
Solid + Liquid
Liquid + Gas

Mixtures

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Gas + Gas
• Example: Air ( Gas + Liquid
N2, O2 , Ar, CO2 • Example:
, other gases) Carbonated
beverages (CO2
Liquid + in water)
Liquid
Solid + Liquid
• Example:
gasoline (a • Example: Sea
mixture of water ( NaCl and
hydrocarbon other salts in
compounds) water)

Solid + Solid + Gas
Solid • Example: H2 in
• Alloys – Homogeneous platinum or
palladium
mixtures of Mixtures
metals
• Example :
brass (Cu/Zn)

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Liquid + Liquid
• EMULSION Solid + Liquid
• Example: milk
• SUSPENSION: Examples:
Tomato juice, jello, blood
• COLLOIDS: Example:
glue, paint

Solid + Solid Solid + Gas
• Example : Gravel
(sand, clay and small • Example: Smoke
rocks) (Air and carbon
particles)
Heterogeneous
Mixtures

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Liquid-Liquid solutions
Example: Example: Example:
Oil and water Phenol and water Ethanol and water

Partially
Immiscible Miscible
miscible

Syllabus requirement met:
define the terms : miscible , immiscible , and
apply them correctly i.e. miscible refers to
liquids

Increasing mixability

25


identify mixtures as solutions
, suspensions , colloids , emulsions

Heterogeneous mixtures based on the states of matter present
and their solubility / miscibility

Solute does not fully dissolve in Solution <Solute particle Liquid + liquid
solvent size< Suspension
Will separate into
Solute particles are clearly Solute particles do not immiscible liquids ONLY if
visible settle out on standing no stabiliser added

Solute particles settle out upon Solute particles can pass
standing through filter paper

Suspensions Colloids Emulsions

Increasing solute particle size

26


Solutions
Solute Solvent Solution
homogeneous
mixture
substance in
The substance
which the
which is being
solute is
dissolved
dissolved

Define solute and solvent

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DECREASING SOLUBILITY

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Table salt dissolving in water
Dissolving.

When a solute dissolves in a
solvent, the particles of the solute
fit in between the particles of the
solvent.

There is no chemical reaction. The
change is reversible and the
essential components of the
mixture remains the same.

Identify dissolving as one
substance fitting in between the
spaces of another substance .

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30


A mixture of different
Separate atoms and
types of atoms and
molecules
molecules

N N N N

O O
Can be
separated by O O O O
PHYSICAL
MEANS into
N N

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SUBLIMATION SOLVENT
• One substance EXTRACTION
sublimes, the other • Differing solubilities
does not in a particular solvent
• Example: • Example: Iodine +
Ammonium chloride sodium chloride
+ sodium chloride

Solid +
solid
mixtures

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FRACTIONAL SEPARATING
DISTILLATION FUNNEL
• Miscible • Immiscible
• Slightly differing • Differing densities
boiling points • Example: Oil + water
• Example: Ethanol +
water

Liquid +
liquid
mixtures

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SOLUTIONS
• EVAPORATION/ CRYSTALLIZATION
• Widely differing boiling points
• Example: Copper sulphate + water
SUSPENSION
• SIMPLE DISTILLATION
COLLOIDS
• DECANTATION.
• Different particle size. • Widely differing boiling points • CHROMATOGRAPHY
• Example – chalk + water • Differing solubilities in a
particular solvent leading
to differing speeds of
• FILTRATION. movement on
• Different particle sizes. chromatogram
• Example: screened methyl
orange

Solid +
Liquid
mixtures

35


Solvent extraction
Are the components
ionic, covalent or
Determinating the correct

mixed?
Does on the Yes
components Sublimation
sublime?

Are the components
in the mixture Do they have Yes Fractional
miscible? differing boiling
distillation
separation technique

points?

Do they have Yes
What is the state of Separating funnel
matter of differing densities?
components in
mixture?

Decantation
Do the components
have widely differing
particle sizes?
Filtration

Is the mixture a Evaporation &
solution, suspension crystallization
or colloid
Do the components
boiling points?
Simple distillation
identify a method of separating
mixtures based on their Chromatography
composition

36


Experiments demonstrating the different methods of separating
mixtures

37


Experiment 1
Question:

You have a mixture of sodium chloride and
ammonium chloride. How would you separate
them?

38


Solvent extraction
Are the components
ionic, covalent or
mixed?
Does on the Yes
sublime?
Determining the correct

Are the components
distillation

points?

Do they have Yes
components in
mixture?

Decantation
Do the components
particle sizes?
Filtration

or colloid
Do the components
boiling points?
Simple distillation

Chromatography

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Materials: •Glass funnel, evaporating dish, Bunsen burner, heating stand
•10g of NH4CL & NaCl mixture

•Place a small amount of the mixture in the evaporating dish.
•Place glass funnel over dish.
Method: •Light bunsen burner until a small even flame is produced.
•Continue heating until no more ammonium chloride is deposited on
the funnel.

Results & •White solid (ammonium chloride) will be deposited on the upper

Observations: sides of the funnel

•The mixture contained 2 ionic solids one of which sublimes (goes
Analysis & from solid to gas) on heating.
•The change is reversible so when the gaseous ammonium chloride
Conclusion: comes into contact with the cooler surface of the glass funnel it
returns to the solid state.

Sublimation

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Experiment 2
Question:

You have a mixture of sodium chloride and iodine
crystals. How would you separate them?

41


Solvent extraction
Are the components
ionic, covalent or
mixed?
Does on the Yes
sublime?

Are the components
distillation

points?

Do they have Yes
components in
mixture?

Decantation
Do the components
particle sizes?
Filtration

or colloid
Do the components
boiling points?
Simple distillation

Chromatography

42


• Two (2) 100 ml beakers, glass stirring rod, evaporating dish, Bunsen
burner, heating stand, filter paper, funnel
Materials: • 10g of iodine crystals (I2) & sodium chloride (NaCl) mixture
• 10 ml of 1,1,1-trichloroethane

•Place 10g of the mixture in beaker.
•Add 10ml of 1,1,1-trichloroethane to beaker.
•Stir with glass stirring rod until all iodine crystals are dissolve
Method: •Fold filter paper into glass funnel. Filter beaker with NaCl, I2 and solvent mixture
into second beaker.
•Light Bunsen burner until a small even flame is produced.
•Heat second beaker with I2/solvent solution until all solvent evaporates.
•Allow residue to cool

•On adding the 1,1,1-trichloroethane, the mixture separates into two layers.
Results & •The top layer is brown in colour. This contains iodine in solution.
•The second layer is a suspension of NaCl in solvent.
Observations: •White crystals are left as filtered residue in filter paper. The filtrate is a brown solution
•On heating, and crystallization, brown crystals are left

Analysis & •The mixture contained one ionic compound (NaCl) which dissolves only in polar solvents such
as water and one molecular compound (i2) which only dissolves in organic solvents.

Conclusion: •The 2 components could therefore be separated by dissolving the molecular compound in the
organic solvent, filtering off the ionic compound and recrystallizing the molecular compound.

Solvent extraction

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Sodium chloride (NaCl)
is ionic and therefore
only dissolves in polar

Solvent extraction
solvents
Sodium chloride
(NaCl (s))

Iodine (I2) is a covalent
compound and therefore
dissolves in organic solvents

Add 1,1,1- Filter off
Mixture of trichloroethane Iodine solution NaCl (s)
iodine + (organic solvent)
sodium chloride
sodium chloride Iodine & solvent
filtrate

Evaporate
the
solvent
through
slow
heating
Syllabus objective Iodine
crystals Cool &
met:
crystallize
identify other
methods of separation
such as solvent
extraction

44


Experiment 3
Question:

You have a solution of copper (II) sulphate and
water. How would you separate them?

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Solvent extraction
Are the components
ionic, covalent or
mixed?
Does on the Yes
sublime?

Are the components
distillation

points?

Do they have Yes
components in
mixture?

Decantation
Do the components
particle sizes?
Filtration

or colloid
Do the components
boiling points?
Simple distillation

Chromatography

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Materials:
•Round bottom flask, thermometer, Bunsen burner, heating stand, Leibig
condenser, Erlynmeyer flask
•10ml of copper (II) sulphate solution - Cu(SO4) (aq)

•Place 10 ml of CuSO4 (aq) into round-bottom flask.

Method:
•Set up the equipment as shown in diagram
•Light Bunsen burner until it achieves a steady blue flame.
•Heat solution steadily until the temperature reaches just above 100 °C.
•Continue to heat until all the solution turns to blue crystals.

Results & •The volume of the solution decreases and changes state (from liquid to solid blue crystals).

Observations:
•A clear solution forms in the Erlenmeyer flask over time.

Analysis &
•The boiling point of water is 100°C while that of CuSO4 is 150°C.
•By keeping the temperature just above 100°C but below 150°C, the water in the solution
changes state from liquid to gas (water vapour).

Conclusion:
•The water vapour travels through the Leibig condenser which cools the temperature and
causes the water to vapour to change back to its liquid state as this is a reversible change.
•The CuSO4 remains in the round bottomed flask as its boiling point has not been reached.

describe the separating methods of simple
distillation Simple distillation

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Thermometer
Heating wire
pad
Round bottom flask

Water out

Bunsen Leibig condenser
burner

Water in
Erlynmeyer flask

Heating stand

Draw line diagrams for simple
distillation
Source: www3.moe.edu.sg/edumall/tl/digital_resources/chemistry/images/simple_distillation2.jpg

48


Experiment 4
Question:

You have a solution of ethanol and water. How
would you separate them?

49


Solvent extraction
Are the components
ionic, covalent or
mixed?
Does on the Yes
sublime?

Are the components
distillation

points?

Do they have Yes
components in
mixture?

Decantation
Do the components
particle sizes?
Filtration

or colloid
Do the components
boiling points?
Simple distillation

Chromatography

50


• Round bottom flask, thermometer, Bunsen burner, heating stand, heating
Materials: pad Leibig condenser, Erlynmeyer flask, fractionating column
• 20ml of ethanol and water solution (50/50 W/V)

•Place 20 ml of solution into round-bottom flask.

Method: •Light Bunsen burner until it achieves a steady blue flame. Heat solution steadily until the
temperature reaches 80°C.
•Continue to heat until all there is no more increases in the volume of distillate collected in the
Erlenmeyer flask

Results & • The volume of the solution decreases by approximately 50%
• A clear solution forms in the Erlenmeyer flask over time which is
Observations: approximately 50% of the original volume.

•The boiling point of water is 100°C while that of ethanol is 78.4°C.

Analysis &
•By keeping the temperature just above 78°C but below 100°C, the ethanol in the solution
changes state from liquid to gas.
•The ethanol vapour travels through the fractionating column, where it is repeated cooled

Conclusion:
and reheated as it falls back into the base of the column, removing impurities.
•The vapour then passes through the Leibig condenser which cools the temperature and
causes the water to vapour to change back to its liquid state as this is a reversible change.
•The water remains in the round bottomed flask as its boiling point has not been reached.

Fractional distillation
describe the separating methods of
fractional distillation

51


Heat is applied to the bottom of the
larger round bottom flask that holds the

Fractional distillation apparatus
fermented mixture.

As the vapors rise in the fractionating
column, the higher boiling point water
condenses and falls back into the round
bottom flask.

The ethanol continues to rise slowly and
reaches the distillation head where a
thermometer registers its temperature.
If the temperature is kept at about 78 C,
by adjusting the heat, ethanol will flow
over to the Liebig condenser and turned
back into a liquid.

The Liebig condenser has a cold water
jacket wrapped around a central tube and
when the hot ethanol vapor comes in
contact with the walls of the inner tube, it
loses heat and returns to a liquid state.

The condensed ethanol drips down and is
collected in the smaller round bottom
flask.

Source: www.chemistrydaily.com/chemistry/upload/1/16/Fractional_distillation_lab_apparatus.png

52


Experiment 5
Question:

You have a solution of oil and water. How would
you separate them?

53


Solvent extraction
Are the components
ionic, covalent or
mixed?
Does on the Yes
sublime?

Are the components
distillation

points?

Do they have Yes
components in
mixture?

Decantation
Do the components
particle sizes?
Filtration

or colloid
Do the components
boiling points?
Simple distillation

Chromatography

54


• Separating funnel, clamp stand, Erlynmeyer flask
Materials: • 20ml of oil and water mixture (50/50 W/V)

•Place 20 ml of solution into separating funnel
Method: •Allow the mixture to settle then slowly release valve and allow the bottom
layer to flow out into the flask below.
•Close valve when the last drop of the bottom layer has been released into
flask.

Results & • The mixture separates into 2 distinct layers.
Observations:

Analysis & • Water has a higher density than oil. It therefore sinks to the bottom of the
separating funnel.
• The two components are highly immiscible, that is they do not mix well with
Conclusion: each other and form a distinctly visible phase boundary between the two
upon settling which allows the easy separation using just the human eye.

Separating funnel
describe the separating methods of
layer separation

55

Set up of separating funnel apparatus

Results of experiment

56


Experiment 6
Question:

You have a mixture of sand and water. How would
you separate them?

57


Solvent extraction
Are the components
ionic, covalent or
mixed?
Does on the Yes
sublime?

Are the components
distillation

points?

Do they have Yes
components in
mixture?

Decantation
Do the components
particle sizes?
Filtration

or colloid
Do the components
boiling points?
Simple distillation

Chromatography

58


• 100ml beaker, 50 ml beaker, glass stirring rod
Materials: • 30ml of sand and water suspension (50/50 W/V)

•Place mixture into 50 ml beaker
•Allow to stand until the sand settles to bottom and the mixture looks fully
Method: transparent.
•Pour the mixture slowly into the 100 ml beaker. Use the glass stirring rod to
prevent any of the sand sediment from being poured into the beaker.

Results & • The mixture went from opaque to transparent with
Observations: white sediment settling to the bottom upon standing.

• The sand and water mixture formed a suspension. The solute, sand, could
not completely mix with the water, i.e. It was partially insoluble.
Analysis & • The sand particles settled to the bottom as it was denser than water and
insoluble.

Conclusion: • The separation of the two components after standing (this process is known
as sedimentation) can be done using just the eye as the separation is very
distinct. However, there is a possibility that some sand particles are left in
the beaker.

Decantation

59


Decantation
Sedimentation Decantation

Source: www.tutorbene.com/cms_images/decantation.bmp

60


Experiment 7
Question:

You have a solution of table salt and water. How
would you retrieve the salt from the solution?

61


Solvent extraction
Are the components
ionic, covalent or
mixed?
Does on the Yes
sublime?

Are the components
distillation

points?

Do they have Yes
components in
mixture?

Decantation
Do the components
particle sizes?
Filtration

or colloid
Do the components
boiling points?
Simple distillation

Chromatography

62


Materials: • Evaporating dish, heating pad, heating stand, Bunsen burner
• 20ml of salt and water solution (50/50 W/V)

•Place solution into evaporating dish
•Set up apparatus as shown in diagram.

Method: •Light Bunsen burner and heat solution slowly, starting with a low flame and
gradually increasing the heat.
•Continue heating until all liquid evaporates.
•Turn off Bunsen burner. Allow residue to cool.

Results & • All water evaporates.
Observations: • The solution gradually turns to solid crystals.

• The water in the solution reaches its boiling point and chnages state from

Analysis &
liquid to gas (water vapour).
• NaCl is an ionic solid which has a very high boiling point as compared to
water and remains in the solid state.
Conclusion: • This method is only useful for separating the mixture’s components when
the solvent (in this case water) is not to be retrieved at the end of the
experiment.

Evaporation/ crystallization

63


Evaporation and crystallization
Salt water
solution Evaporating dish

Heating pad or wire gauze

Heating stand or
tripod

Bunsen burner

Source: www3.moe.edu.sg/edumall/tl/digital_resources/chemistry/images/evaporation.jpg

64


Experiment 8
Question:

You have a solution of chalk and water. How
would you retrieve both components of the
mixture?

65


Solvent extraction
Are the components
ionic, covalent or
mixed?
Does on the Yes
sublime?

Are the components
distillation

points?

Do they have Yes
components in
mixture?

Decantation
Do the components
particle sizes?
Filtration

or colloid
Do the components
boiling points?
Simple distillation

Chromatography

66


Materials: • Filter paper, funnel, 100 ml beaker, Erlenmeyer flask
• 30ml of chalk and water solution (50/50 W/V)

•Place mixture into 100 ml beaker
•Fold filter paper as shown in diagram below
•Place in funnel then place funnel into Erlenmeyer flask
Method: •Pour mixture into funnel slowly until the entire mixture is transferred
without spilling out of funnel.
•Allow the mixture to separate out completely before removing the filter
paper.

Results & • The chalk remains as residue on the filter paper
Observations: • The water comes out in the Erlenmeyer flask

• The chalk and water mixture formed a suspension. The
solute, chalk, could not completely mix with the water, i.e. It was
partially insoluble.
Analysis & • The chalk particles are larger than the water molecules and cannot
pass through the porous filter paper.
Conclusion: • The water molecules are small enough to pas s through the filter
paper.
• This difference in particle size allows the chalk to be separated from
the water via the process of filtration.

1. describe the separating methods of filtration
2. carry out filtration in the laboratory and write up notes about the
procedure and results
3. recognize that filtration separates particle based on size
Filtration

67


Procedure for fluted filter paper
This is used when you need to get
faster filtration.

Source: www.theresasakno.com/popup/popup.asp?sid=D674F0CE-C7CB-4A46-94EA-1E79AD64C378&imgname=034.jpg

68

Water molecules

Beaker

Filter paper
Filter
paper

Mixture of chalk
and water
(suspension)
Chalk particles

The water molecules Beaker
are smaller than the Water
chalk particles. They
are small enough to
pass through the
pores of the filter
paper. Funnel

Source: www3.moe.edu.sg/edumall/tl/digital_resources/chemistry/images/filtration.jpg

69


How to filtrate a hot solution
Materials required:
1. Clamp stand,
2. Short stem glass funnel
3. Glass stirring rod
4. Filter paper (fluted)
5. Erlenmeyer flask
6. Cloth

A filtration procedure called "hot gravity
filtration" is used to separate insoluble
impurities from a hot solution.

Hot filtrations require fluted filter paper
and careful attention to the procedure to
keep the apparatus warm but covered so
that solvent does not evaporate

Source: www.chemistry.mcmaster.ca/~chem2o6/labmanual/expt1/exp1-f3.gif

70


Vacuum Filtration
Vacuum filtration is used primarily to collect a
desired solid, for instance, the collection of
crystals in a recrystallization procedure.

Vacuum filtration uses either a Buchner or a
Hirsch funnel.

Vacuum filtration is faster than gravity
filtration, because the solvent or solution and air
is forced through the filter paper by the
application of reduced pressure. The reduced
pressure requires that they be carried out in
special equipment:
1. Buchner or Hirsch funnel
2. heavy-walled, side arm filtering flask
3. rubber adaptor or stopper to seal the funnel to
the flask when under vacuum
4. vacuum source

Source: http://blog.khymos.org/wp-content/2007/09/stock-filtration.png

71


Experiment 9
Question:

How would you separate the pigments in screened
methyl orange?

72


Solvent extraction
Are the components
ionic, covalent or
mixed?
Does on the Yes
sublime?

Are the components
distillation

points?

Do they have Yes
components in
mixture?

Decantation
Do the components
particle sizes?
Filtration

or colloid
Do the components
boiling points?
Simple distillation

Chromatography

73


• Chromatography paper,, glass rod, beaker
Materials: • 5ml screened methyl orange, 50ml water

•Screened methyl orange is dissolved in water and carefully spotted
onto chromatography paper
•Alongside it are spotted known colours on a 'start line'
•The paper is carefully dipped into water, which is absorbed into the
Method: paper and rises up it.
•The distance moved by the solvent is marked on carefully with a pencil
and the distances moved by each 'centre' of the coloured spots is also
measured

• Two different colours appear on the chromotogram at different points
Results & on the paper.
• Rf = distance moved by dissolved substance (solute) / distance moved
Observations: by solvent.
• The Rf value is calculated for each spot.

Analysis & • Due to different solubilities and different molecular 'adhesion' some
colours move more than others up the paper, so effecting the
Conclusion: separation of the different coloured molecules.


Chromatography
identify other methods of separation
such as chromatography

74


These are
the
pigments

Chromatography present
in the dye

The material to be separated e.g. a food
dye (6) is dissolved in a solvent and
carefully spotted onto chromatography
paper sheet. Alongside it are spotted
known colours on a 'start line' (1-5).

The paper is carefully dipped into a
solvent, which is absorbed into the paper
and rises up it. The solvent may be water
or an organic liquid like an alcohol (e.g.
ethanol) or a hydrocarbon, so-called non-
aqueous solvents.

For accurate work the distance moved
by the solvent is marked on carefully Any colour which horizontally matches
with a pencil and the distances moved by another is likely to be the same molecule
each 'centre' of the coloured spots is also i.e. red (1 and 6),
measured. These can be compared with brown (3 and 6) and
known substances BUT if so, the blue (4 and 6) match,
identical paper and solvent must be used showing these three are all in the food dye (6).

75


Methods used in industry for separating mixtures

76


Chromatography
Calculation of Rf values

The distance a substance moves, compared to the distance the
solvent front moves is called the reference or Rf value

0.0<Rf<1.0 where
Rf = 0.0 (not moved - no good)
Rf = 1.0 (too soluble - no good either)

Rf ratio values between 0.1 and 0.9 can be useful for analysis
and identification.

distance distance
moved by moved by
Rf dissolved solvent
substance
(solute)

Chromatography can be used to
separate the amino acids in proteins

and to separate drugs in pharmaceutical
laboratories

77


Centrifugation is a process that
involves the use of the centrifugal force
for the separation of mixtures, used in
industry and in laboratory settings.

More-dense components of the mixture

Centrifugation
migrate away from the axis of the
centrifuge, while less-dense components
of the mixture migrate towards the axis.

Increasing the effective gravitational
force on a test tube causes the precipitate
to gather on the bottom of the tube.

The remaining solution is properly called
the "supernate" .The supernate is then
either quickly decanted from the tube
without disturbing the precipitate, or
withdrawn with a pipette

Source: http://www.freewebs.com/ltaing/centrifuge2.gif

78


Centrifugation is used to
separate the components in
blood

Centrifugation of blood
A centrifuge separates out blood
components by their various
densities.

The red blood cells (RBCs) are
denser and move to the bottom
of the tube.

The plasma fraction is the least
dense and will float as the top
layer.

The "buffy coat" which contains
the majority of platelets will be
sandwiched between the plasma
and above the RBCs.

Name two industrial methods of separating mixtures - centrifugation used to
separate components of blood / body fluids in laboratory testing

79


Fractional distillation in industry
Continuous fractionating How it works
column
This is an industrial fractionating
column separating a feed stream into
one distillate fraction and one bottoms
fraction.

However, many industrial fractionating
columns have outlets at intervals up the
column so that multiple products
having different boiling ranges may be
withdrawn from a column distilling a
multi-component feed stream.

The "lightest" products with the lowest
boiling points exit from the top of the
columns and the "heaviest" products
with the highest boiling points exit from
the bottom.

80


Fractionating columns in industry
Bubble cap trays in
How it works
fractionating columns
Bubble-cap "trays" or "plates" are
one of the types of physical
devices which are used to provide
good contact between the up-
flowing vapour and the down-
flowing liquid inside an industrial
fractionating column

Syllabus requirements met:
Name two industrial methods of separating mixtures e.g.
fractional distillation used to obtained distilled spirits

Separating Mixtures: Techniques and Everyday Applications

Separating Mixtures: Techniques and Everyday Applications

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