Ppt colloidsppt 21

COLLOIDS
PRESENTED BY:
Dr. Seema S. Pattanshetti
Assistant Professor of Chemistry
S.Nijalingappa Sugar Institute,
College of B.Sc. (Sugar Science & Technology), Belagavi

C
O
L
L
O
IDS
 A colloid is a substance microscopically dispersed
throughout another substance.
 The word colloid comes from a Greek word
'kolla', which means glue thus colloidal
particles are glue like substances.
 Colloidal solutions are mixture of
microscopically dispersed insoluble
particles of one substance are suspended
in another substance.
 These particles pass through a filter paper but not
through a semipermeable membrane.
 Colloids can be made settle by the process of
centrifugation.The size of suspended particles in
colloid can ranges from 1 to 1000 nanometers
 (10-9 mts)

 The dispersed-phase particles have a diameter of
between approximately 1nm – 100nm .
 Such particles are normally invisible in an optical,
though their presence can be confirmed with the
use of an ultramicroscopeor anelectron
microscope.
The colloidal system consists of two
phases
 A dispersed phase( discontinuous
phase )
 A dispersion medium ( continuous
phase )

SOLUTIONS
 Made up of particles or solutes and a solvent
 The solvent part of the solution is usually a
liquid, but can be a gas.
 The particles are atoms, ions, or molecules that
are very small in diameter.
COLLOIDAL MIXTURE
Has particles that are not as small as a solution
and not as large as a suspension.
 The particles are intermediate in size.
SUSPENSIONS
 Made up of particles and a solvent
its particles are larger than those found in a
solution.
 The particles in a suspension can be distributed
throughout the suspension evenly by shaking the
mixture.

ComparisonofthePropertiesof
Solutions,Colloids,And Suspensions
Property True Solution Colloid Suspension
Particle Size Less than 1 nm 1 to 100 nm More than 100 nm
Appearance Clear Cloudy Cloudy
Homogeneity Homogeneous Homogeneous or
Heterogeneous
Heterogeneous
Transparency Transparent but
often coloured
Often translucent
and opaque but can
be transparent
Often opaque but
can be translucent
Separation Does not separate Can be seperated Separates or settles
Filterability Passes through filter
paper
Passes through filter
paper
Particles do not
pass through filter
paper

Examples of colloids are milk, synthetic
polymers, fog, blood, jam, shoe polish, smoke etc.

The following forces play an important role in
the interaction of colloid particles:
EXCLUDED VOLUME REPULSION IN
LIQUID THEORY :
In liquid state theory, the 'excluded
volume' of a molecule is the volume
that is inaccessible to other molecules
in the system as a result of the presence
of the first molecule.
The excluded volume of a hard
sphere is eight times its It is
the sum of the attractive or
repulsive

It is the sum of the attractive or
Repulsive forces between molecules other
than those due to covalent bonds, the
hydrogen bonds,or the electrostatic
interaction of ions with one another
molecules.
• Colloidal particles often carry an
electrical charge an therefore attract or
repel each other.
The charges of both the continuous
and the dispersed phase as well as
the mobility of the phases are
factors affecting from the fact that each
atom within a molecule

Each atom occupies a
certain amount of space.
If atoms are brought too close
together, there is an associated
cost in energy due to overlapping
electron clouds (Pauli or Born
repulsion), and this may affect
the molecule's preferred shape
(conformation) and reactivity.
Steric force

CLASSIFICATION OF
COLLOIDS
 Based of physical state of dispersed phase an dispersion
medium.
 Based of nature of interaction between dispersed phase and
dispersion medium.
 Based on molecular size in the dispersed phase.
 Based on appearance of colloids.
 Based on electric charge on dispersion phase.

Based on physical state of dispersed
phase and dispersion
medium

BASED ON NATURE OF INTERACTION BETWEEN
DISPERSED PHASE AND DISPERSION MEDIUM
LYOPHILIC COLLOIDS
 Colloidal solution in which the dispersed phase
has a great affinity for the dispersion medium.
 They are also termed as intrinsic colloids.
 Such substances have tendency to pass into
colloidal solution when brought in contact with
dispersion medium.
 If the dispersion medium is water, they are
called hydrophilic or emulsoids.
 The lyophilic colloids are generally self-
stabilized.
 Reversible in nature and are heavily hydrated.
 Example of lyophilic colloids are starch,
gelatin, rubber, protein etc.

LYOPHOBIC COLLOIDS
 Colloidal solutions in which the dispersed phase has no
affinity to the dispersion medium.
 These are also referred as extrinsiccolloids.
 Such substances have no tendency to pass into colloidal
solution when brought in contact with dispersion medium.
 The lyophobic colloids are relativelyunstable.
 They are irreversible by nature and arestabilized by
adding small amount ofelectrolyte.
 They are poorly hydrated.
 If the dispersion medium is water, the lyophobiccolloids
are called hyrophobic or suspenoids.
 Examples: sols of metals like Au,Ag,sols of metal
hyroxides and sols of metal sulphides.

Based on molecular size in the dispersed
phase.
 MULTIMOLECULAR
COLLOIDS
Individual particles of the dispersed
phase consists of aggregates of atoms
or small molecules having diameter less
than 10-7cm . The particles are held by
weak vander waal’s forces.
Example; gold sol, sulphur sol
MACROMOLECULAR
COLLOIDS
The particles of dispersed phase are
sufficiently large in size enough
to be of colloidal solution. These
are called Natural Polymers.

ASSOCIATED COLLOIDS
These colloids behave as normal
electrolytes at low concentrations but
behave as colloids at higher
concentrations.
These associated colloids are also
referred to as micelles.
Sodium stearate (C18H35NaO2)behave
as electrolyte in dilute solution but
colloid in higher concentrations.
Examples: Soaps , higher alkyl
sulphonates , polythene oxide.

HOW DOESSOAPWORK?
• When greasy dirt is mixed with
soapy water, the soap molecules
arrange themselves into tiny clusters
called micelles.
• The water-loving (hydrophilic) part of
the soap molecules sticks to the water
and points outwards, forming the outer
surface of the micelle.
• The oil-loving (hydrophobic) parts
stick to the oil and trap oil in the
center where it can't come into contact
with the water. With the oil tucked
safely in the center, the micelle formed
will be removed out with water as dirt
water.

Based on appearance of colloids
• SOLS


 When a colloidal solution appears as fluid.
 The sols are generally named as dispersion medium.
When the dispersion medium is water, the sol iss known as
hydrosol or aquosol.
When the dispersion medium is alcohol or benzene it is
called alcosol and benzosol respectively.
• GELS

When a colloidal solution appear as solid. An gel is jelly
ice colloidal System in which a liquid is dispersed in a
Solid medium.
The word gel was coined by Scottish Chemist in 19th
century named Thomas Graham.
The rigidity of gel varies from substance to substance.
Examples : jelly, butter, cheese, curd.

GELS
These are solid jelly like material that can have properties that can have properties
ranging from soft and weak to hard and tough.
Gels can be defined As a Substance to A dilute cross-linked System, which exhibits
no flow when in the steady State.
These are Aggregate of fine particles dispersed in a Continues System. In this liquid
medium has become enough to behave more or less solid.
When a warm solution of gelatine is cooled, it sets to a semisolid mass which is gel,
the process of a gel formation is known as Gelation.
Explanation: Here Gelatine may be thought of an partial coagulation of soil. The
coagulating soil Particle first unites to form long thread like chains. These chains are
then interlocked to form a solid framework. The liquid dispersion medium gets trapped
in the cavities of this framework. The resulting Semisolid porous mass has a gel
structure A Sponse Soaked in water is an illustration of gel Structure.

Foams
•Foams are formed when may gas particles are trapped in a liquid or solid.
•Foam is an object formed by trapping pockets of gas in a liquid or solid. A bath
sponge and the head on a glass of beer are examples of foams. In most foams, the
volume of gas is large, with thin films of liquid or solid separating the regions of gas.
•Foam, in physical chemistry, a colloidal system (i.e., a dispersion of particles in a
continuous medium) in which the particles are gas bubbles and the medium is a liquid.
... The term also is applied to material in a lightweight cellular spongy or rigid form.
Examples of foams formed by gases in liquids include whipped cream, fire
retardant foam, and soap bubbles. Rising bread dough may be considered a
semisolid foam. Solid foams include dry wood, polystyrene foam, memory foam, and
mat foam (as for camping and yoga mats).
Aerosol – Contains Small Particles of liquid Solid dispersed in a gas.
Ex: Fog and many Sprays. Solid gas (smoke)

Types:
Gels may be classified into two types –Elastic Gel & Non-Elastic gel
Elastic gel: These are the gels which posses the property of elasticity. They change
their Shape on Applying force And Return to original Shape when force is removed.
Ex : Gelatin, Starch, Soaps, Agarbatti .
Here linkage between molecules (particles) Are due to electrical attraction and are
not rigid.
Non-Elastic Gel : These are those which are rigid. These are prepared by
appropriate chemical action.
Ex: Silica gel – It is produced by adding con.HCL to Sodium Silicate Solution of the
correct concentration. The resulting of molecules of acid polysynthetic to form silica
gel. These non-Elastic gels have network linked by co talented bonds which gives
strong and rigid Structure.

Emulsions
An emulsion is a dispersion of a liquid in a liquid.
Ex: Milk lotions.
Generally it is a type of fine dispersion of minute droplet of one liquid in another in which it is not soluble
or miscible.
These are the mixture of 2or more liquids that are normally immiscible. (unmixable or unbendable).
Emulsions are part of a more general class of 2-phase system of matter called Colloids. An emulsion may
be defined as a dispersion of finely divided liquid droplets in another liquid.
Types of emulsions –
There are 2 types of emulsions
Oil in water type (o/w type) , Water in oil type (w/o type)

Emulgents
Emulsion (Emulgent) :
A substance or compound at acts as a stabilizer for emulsions preventing liquid that
ordinaririly don’t mix from separating.
The form emulsifier may also refer to an apparatus that shares or stirs ingrdients to
form an emulsion. the Substance that stabilizes the emulsion.
Ex : Detergent, egg yolk.

Preparation of Gels:
Gels can be prepared By following method:
1.Thermal changes: when solvated ploy mix or lipoplilic. Colloid when subjected to
thermal process or change causes gelatine. If the temperature and lowered, the degree
of hydration of acidophilic colloid is reduced and gelatine occurs gelatine , sodium
coblate, gurgum and cellulose derivatives.
2.Flocculation : In Flocculation, gelation is produced by adding gust enough quantity of
salt to participate to bring about complete precipitation.
Ex: solution of ethyl cellulose. Polystyrene in benzene can be gelled by rapid mixing c
Suitable amounts of non-solvent such as petroleum either.
3.Chemical Reaction: Here gel is prepared by chemical reaction between Solutes
Solvent.
Aluminium hydroxide gel is precipated by interaction in the Solution of an aluminium
Salt and Sodium carbonate.
Here an increased concentration of reactants will produce a gel structure.

Properties of gels:
1. Hydration: A completely dehydrated elastic gel can be regenerated by addition of
water. But once a non Elastic gel is freed from moisture addition of water not brings
about gelatine.
2.Swelling: Partially dehydrate elastic gala imbibe or absorb water when immersed in
solvent. This causes increase in the volume of the gel and process is called swelling.
3.Syneresis: Many inorganic gels on standing undergo this process which is
accompanied by exudation of solvent this process is termed syneresis.
4.Thixotropy: Some gels are semisolid when at rest but revert to liquid solution on
agitation. This reversible sol-gel transformation is referred to thyrotrophic.
Iron oxide and silver oxide gels exit this property. The modern thyrotrophic paints are
also as example.
It is time dependent shear thinning property certain or fluid that are thick viscous under
static condition and flow become thin, less viscous) over time when Agitated or
stressed.
Agitation is the Set of Stirring things up.
Ex: washing machine that moves the water detergent and clothes around and gets the
dirt out.

BASED ON ELECTRICAL CHARGE ON
DISPERSION PHASE
 POSITIVE COLLOIDS
When dispersed phase in a
colloidal solution carries a
positive charge.
Examples : Metal hyroxides like
Fe(OH)3,
Al(OH)2, methylene blue sol etc.
 NEGATIVE COLLOIDS
When dispersed phase in a colloidal
solution carries a negative charge.
Examples : Ag sol, Cu sol

SEPERATION OF COLLOIDS
Mechanical Dispersion
Electrical dispersion or Bredig’s Arc
Method
Peptisation
Condensation Method

A) Mechanical dispersion:
In this method,
The substance is first ground to coarse particles.
It is then mixed with the dispersion medium to get
a suspension.
 The suspension is then grinded in colloidalmill.
It consists of two metallic discs nearly touching
each other and rotating in opposite directions at a
very high speed about 7000 revolution per minute.
The space between the discs of the mill is so
adjusted that coarse suspension is subjected to great
shearing force giving rise to particles of colloidal size.
Colloidal solutions of black ink, paints, varnishes,
dyes etc. are obtained by this method.

(B) By electrical dispersion or Bredig’s arc
method:
This method is used to prepare solsof
platinum, silver, copper or gold.
The metal whose sol is to be prepared ismade
as two electrodes which immerge in dispersion
medium such as water etc.
The dispersion medium is kept cooled byice.
An electric arc is struck betweenthe
electrodes.
The tremendous heat generated by thismethod
give colloidal solution.
The colloidal solution prepared is stabilizedby
adding a small amount of KOHto it.

(C) By peptisation:
The process of converting a freshly prepared precipitate intocolloidal form
by the addition of suitable electrolyte is called peptisation.
Cause of peptisation is the adsorption of the ions of theelectrolyte by the
particles of the precipitate.
The electrolyte used for this purpose is called peptizing agent orstabilizing
agent.
 Important peptizing agents are sugar, gum, gelatin and electrolytes.

(D) Condensation method
 In condensation method, the
smaller particles of the dispersed
phase are aggregated to form
larger particles of colloidal
dimensions.
 Some important condensation
methods are described below:
a) Solutions of substances like mercury
and sulphur are prepared by passing
their vapours through a cold water
containing a suitable stabilizer such as
ammonium salt or citrate.

b)Byexcessivecooling:
Acolloidal solution of ice in an organic solvent like ether or
chloroform can be prepared by freezing a solution of waterin
solvent.
The molecules of water which can no longer be held insolution,
separately combine to form particles of colloidal size.
c)Byexchangeofsolvent:
Colloidal solution of certain substances such as sulphur, phosphorus which are soluble
in alcohol but insoluble in water can be prepared by pouring their alcoholic solution in
excess of water.
For example alcoholic solution of sulphur on pouring into water gives milky colloidal
solution of sulphur.

d) Chemical methods:
Colloids can be prepared by following chemicals
methods..
1)
Oxidation:
Addition of oxygen and removal of hydrogen is calledoxidation.
For example: Colloidal solution of sulphur can be prepared by oxidizing an aqueous
solution of H2S with a suitable oxidizing agent such as bromine water.
H2S + Br2 → 2HBr + S
2H2S + SO2 → 2H2O + 3S

2)Reduction:
Addition of hydrogen and removal of oxygen is called
reduction.
For example: Gold sol can be obtained by reducing a
dilute aqueous solution of gold with stannous chloride.
2AuCl3 + 3SnCl2 → 3SnCl4 + 2Au
3) Hydrolysis:
It is the break down of water.
Sols of ferric hydroxide and aluminium hydroxide can be
prepared by boiling the aqueous solution of the corresponding
chlorides.
For example.
FeCl3 + 3H2S → Fe(OH)3+ 3HCl

4) Double
Decompostion
The sols of inorganic insoluble salts such as arsenous sulphide,
silver halide etc may be prepared by using double decomposition
reaction.
For example: Arsenous sulphide sol can be prepared by passing
H2S gas through a dilute aqueous solution of arsenous oxide.
As2O3 + 3H2S → As2S3(OH)3 + 3H2O

PHYSICAL PROPERTIES OF COLLOIDS
• Heterogeneity: Colloidal solutions consist of two phases-dispersed
phase
and dispersion medium.
• Visibility of dispersed particles:The dispersed particles present
in them are not visible to the naked eye and they appear
homogenous.
• Filterability: The colloidal particles pass through an ordinary filter
paper. However, they can be retained by animal membranes,
cellophane membrane and ultrafilters.
• Stability: Lyophilic sols in general and lyophobic sols in the
absence of substantial concentrations of electrolytes are quite
stable.
• Colour: The colour of a colloidal solution depends upon the size of
colloidal particles present in it. Larger particles absorb the light of
longer wavelength and therefore transmit light of shorter wavelength.

OPTICAL PROPERTIES
OFCOLLOIDS
• TYNDALL EFFECT
• When an intense converging beam of light is
passed through a colloidal solution kept in
dark, the path of the beam gets illuminated
with a bluish light.
• This phenomenon is called Tyndall effect
and the illuminated path is known as
Tyndall cone.
• The Tyndall effect is due to the scattering of light
by
colloidal particles.
• Tyndall effect is not exhibited by true solutions.
This is because the particles present in a true
solution aretoo small to scatter light.
• Tyndall effect can be used to distinguish a
colloidal solution from a true solution. The
phenomenon has also been used to devise an
instrument known as ultra microscope. The
instrument is used for the detection of the
particles of colloidal dimensions.

MECHANICAL PROPERTIES OF
COLLOIDS
• BROWNIAN MOVEMENT
• The continuous zigzag movement of the colloidal
particles in the dispersion medium in a colloidal
solution is called Brownian movement.
• Brownian movement is due to the unequal
bombardments of the moving molecules of
dispersion medium on colloidalparticles.
• The Brownian movement decreases with an
increase in the size of colloidal particle. This is why
suspensions do not exhibit this type ofmovement.

ELECTRICAL PROPERTIES OF
COLLOIDS
• ELECTROPHORESIS
• The movement of colloidal particles
towards a particular electrode under
the influence of an electric field.
• If the colloidal particles carry positive
charge, they move towards cathode
when subjected to an electric field
and vice versa.

• ELECTROSMOSIS
• The movement of dispersion medium under the influence of an
electric field in the situation when the movement of colloidal
particles is prevented with the help of a suitable membrane.
• During electrosmosis, colloidal particles are checked and it is the
dispersion medium that moves towards the oppositely charged
electrode.

• COAGULATION OR
FLOCCULATION
• Coagulation
defined
may be
as the
phenomenon involving the
precipitation of a colloidal
solution on addition of an
electrolyte.
• Hardy-Schulze rule
The greater is the
valence of the oppositely
charged ion
electrolyte
of the
added to a
medium.

• Flocculationvalue:The coagulating power of an electrolyte is usually
expressed in terms of its flocculation value which may be defined as the
minimum concentration (in millimoles per litre) of an electrolyte required to
cause the coagulation of a sol.
• Asmaller flocculation value indicates the greater coagulating power ofthe
electrolyte. Thus,
Coagulatingpowerα 1
Flocculationvalue
• The coagulation of colloidal solution can also be achieved by anyof the
following methods.
Byelectrophoresis
Bymixing twooppositelysols
Bypersistentdialysis

Biologicalsignificanceofcolloidal systems
• Protoplasm is a Colloidal
system:
• Protoplasm is
colloidal nature.
• Amoeboid movements:
Amoeboid
movements in
amoeba occur

• Fruits:
Turns store a large amount of
proteins and
starch. They also exhibit
colloidal properties.
• Blood:
High plasma protein forms a
colloidal
system in blood. This
system maintains the
pH and osmotic
concentration of blood.

ADVANTAGES OF COLLOIDS
Colloids allow the dispersion of normally insoluble
materials, such as metallic gold or fats. These can
then be used more easily, or absorbed more easily.
Colloidal gold, for example, can be used in
medicine to carry drugs and antibiotics, because it is
highly non-reactive and non-toxic.
Pharmaceutical industry makes use of colloidal
solution preparation in many medicines. A wide
variety of medicines are emulsions. An example is
Cod Liver Oil.
Paint industry also uses colloids in the preparation
of paints.

In milk, the colloidal suspension of the fatsprevents
the milk from being thick, and allows for easy
absorption of the nutrients.
Sewage water contains particles of dirt, mud etc.
which are colloidal in nature and carry some electrical
charge. These particles may be removed by using the
phenomenon of electrophoresis.
The sky is the empty space around earth andas such
has no colour. It appears blue due to the scattering of
light by the colloidal dust particles present in air
(Tyndall effect).
Asphalt emulsified in water and is used forbuilding
roads.

The sugar present in milk produces lactic acid on
fermentation. Ions produced by acid, destroy the
charge on the colloidal particles present in milk,
which then coagulate and separate ascurd.
Soap solution is colloidal in nature. It removes the
dirt particles either by adsorption or by emulsifying
the greasy matter sticking to the cloth.
Large numbers of food particles which we use in
our daily life are colloidal in nature.
Example: Milk, butter, &ice cream etc

General application of Colloids
.
Colloids play on important role in our daily life and industry. Knowledge of colloid chemistry
is essential to understand some of the various natural phenomena around us.
There are few important applications of colloids are:-
Foods: Many of our foods are colloidal in nature. Milk is an emulsion of butterfat in water
protected by a protein, casein. Salad dressing, gelatine desserts, fruit salad and whipped cream
are the examples.
Ex : Ice-cream dispersion of ice-cream
Bread is dispersion of air in baked dough
Medicine: Colloidal medicines being finely divided are more effective and are easily absorbed
in our system. Many ointments for application to skin consist of physiologically active
components dissolved in oil and made into emulsion water.
Non-Drip paints: All most non-drip or thyrotrophic paints also contains long chain polymers.
At rest the chain of molecules are coiled and entrap much dispersion medium. Thus the paints
semisolid gel structure when shearing stress applied a paint brush, the coiled molecules
straighten and entrapped medium is released. As soon as brush is removed the liquid paint
reverted to the semisolid from this renders the paint non-trip.
.

General application of Colloids
Electrical precipitation of smoke:
the smoke from industry is an example of colloids state before allowing the smoke to
escape into air it is treated by Cottrell precipitator. The smoke is let past a series of
sharp points charged to potential 9200 to 70000v. The points discharge high velocity
electron that ionise molecules in air. Smoke particles absorb these tve ion and become
charged. The charged particles are attracted to oppositely charged electrons and get
precipitated. The gases that leave the Cottrell precipitator are free from smoke.
Ex : Arsenic oxide is mainly recovered from smelter smoke by this method.

Applications
Clarification of municipal water – the municipal waste water always contains
colloidal. The coagulation method is used to remove this. The solution carry change.
When aluminium sup hate (alum) is added to water, a gelatinous ppt of hydrated
aluminium hydroxide is formed.
Al+3+3H20  H(OH)3+3H+
Here the positively charged hoc attracts to it negative solution particles which are
coagulated. The hoc along c- the suspended matter comes down, leaving the water
clear.

Questions
Two marks
1. What are colloids?
2. What are the types of colloids?
3. What are emulsions?
4. What is gel? Give an example
5. What are emulsifiers? Give an example
6. Explain the non-dripping of paints.
7. Define Syneresis.
8. What are gels?
9. What are foams?
Five Marks
1. Write the general application of colloids.
2. What are the types of gels ? Explain types with the examples.
3. Define the process of Emulsification . Explain the types of emulsions.

Ppt colloidsppt 21

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Ppt colloidsppt 21