COLLOIDS
Prepared by
Prof. Odyssa Natividad RM. Molo
CONTENT
• History
• Preparation
• Components
• Purification
• Classification
• Applications
• Properties
• Chemical Impact
Colloids History
 Thomas Graham (1861) while doing his classical researches
on liquid diffusion observed two classes of substances
 Crystalloid: readily pass through animal & vegetable
membrances
 Colloids: diffused very slowly & could not pass through
membrane
 Came from the Greek word kola which means “glue-like”
COLLOIDS
• aka colloidal dispersion
• Heterogeneous mixture which has suspended
tiny particles
• Particles size: solution < colloid < suspension
• Can pass through filters but are too large to
pass through membranes.
• Distinguished from a true solution through
Tyndall effect
TYNDALL EFFECT
The scattering of light.
Although undetected in
normal lightning, presence
of the small particles that
remain suspended can be
demonstrated by shining a
beam of intense light. The
beam is visible from the side
because light is scattered by
the suspended particles.
What stabilizes a colloid?
Why do the particles remain
suspended rather than form larger
aggregates and precipitate out?
The answer is complicated, but the
main factor seem to be electrostatic
repulsion.
What stabilizes a colloid?
 A colloid, like all other macroscopic
substances, is electrically neutral.
 However, when a colloid is placed in an
electric field, the dispersed particles all
migrate to the same electrode and thus
must all have the same charge
(electrophoresis).
How is this possible?
The center of a colloidal particles (a tiny ionic crystal, a group of
molecules or a single large molecule) attracts from the medium a layer
of ions, all of the same charge. This group of ions, in turn, attracts
another layer of oppositely charged ions. Because the colloidal particles
all have an outer layer of ions with the same charge, they repel each
other and do not easily aggregate to form particles that are large
enough to precipitate
Components of Colloids
 Colloidal particles/Dispersed phase/substance
 Similar to solute in solution
 Discontinuous phase
 Dispersion/dispersing medium
 Similar to solvent in solution
 Continuous phase
Classification of Colloids
(based on states of dispersed phase & dispersion medium)
COLLOID TYPE
DISPERSE
D PHASE
DISPERSIN
G MEDIUM
EXAMPLE
Aerosol (liq aerosol)
Liquid
Gas
Mist, fog, clouds, spray
Aerosol (solid aerosol)
Solid
Gas
Dust, smoke, airborne bacteria,
fume
Foam
Gas
Liquid
Whipped cream, soap suds, shaving
cream, froth
Emulsion
Liquid
Liquid
Milk, mayonnaise, hand lotion
Sol
Solid
Liquid
Paint, clay, blood plasma, gelatin,
starch paste, glue
Solid foam
Gas
Solid
Marshmallow, styrofoam, pumice
stone, bread dough
Solid emulsion or gel
Liquid
Solid
Butter, cheese, gelatin, curd
Solid sol
Solid
Solid
Ruby glass, gemstone, cement
Classification of Colloids
(based on affinity for solvent)
 Lyophilic colloid
 There is a strong affinity between the dispersed
phase & the dispersion medium
 Lyophobic colloid
 There is no apparent affinity
 If solvent if water:
 Hydrophilic (water-loving)& hydrophobic
Characteristics of lyophilic & lyophobic
LYOPHILIC
LYOPHOBIC
Stable
Unstable
The particles may or may not migrate in an
electrical field
The particles are charged and hence move
towards electrode in an electrical field
Viscosity is much higher than that of the
medium
Viscosity is same as that of the medium
Reversible
Irreversible
Self-stabilized due to strong attraction
between 2 phases
Stabilizer is required
Not easily precipitated by the addition of
electrolytes
Coagulated easily by adding electrolytes
Not visible under ultramicroscope
Visible under ultramicroscope
Prepared by directly dissolving
Prepared by indirect method
Some Properties of Colloids
Tyndall Effect
Brownian movement
Adsorption
Electrical charge
Tyndall effect
• Discovered in the course of his study into light beams by British
physicists JohnTyndall
 Exhibited by colloid: both beneficial & harmful
 Brilliant colors at sunset and the blue color of the sky and the
sea are caused by thick layer of small particles and molecules in
the atmosphere and in the sea.
 Smoke, fog, mist and smog are colloids which pollute the
atmosphere.
Brownian movement/motion
 Is the rapid, haphazard zigzag motion of colloidal
particles caused by the collision of colloidal particles
with the molecules of the dispersion medium.
 Colloidal particles do not settle
because of this.
 First observed under a special microscope by Robert
Brown, a Scottish botanist, when he suspended
pollen grains in water.
Adsorption
 Is the binding in thin layer of molecules to
the surface.
 Use/application:
 activated carbon to remove unpleasant
odors and flavors,
 cigarette filters to remove carcinogenic
compounds in the smoke, and
 gas masks to provide protection against
toxic or irritating gases.
Electrical charge
• Colloidal particles adsorb charged particles (ions)
from their surrounding medium.
• Colloids are either (+) or (-) ions, but within a
system, all particles have the same electrical charged
so they repel each other.
• Prevents colloids from forming aggregates or
precipitates, making the system stable.
• When colloids attract other colloids of opposite
charge, precipitation or coagulation occurs.
Electrical charge application
 In industries, (electrostatic/Cottrell precipitator) used to
remove soot particles and other suspended solids from gases
in smokestacks before they are released to the atmosphere.
 Charged plates are placed inside the smokestack
where they attract the charged colloidal particles
which are held or precipitated on the plates. When
current is turned off, particles fall from the plates are
then collected.
How electrostatic precipitator works
1)
2)
3)
Smoke particles pick
up a negative charge.
Smoke particles are
attracted to the
collecting plates.
Collecting plates are
knocked down to
remove the smoke
particles.
How photocopier/laser printer works
Preparation of Colloids
 Dispersion
 Large particles are broken down to colloidal
dimension & dispersing them to colloidal
solution
 Condensation
 Particles of molecular size are allowed to
coalesce or condense to form bigger
particles of colloidal size
Dispersion
 Breaking down of big particles by grinding
or by ultrasonics (use of high-intensity
acoustic energy)
 Usually leads to extensive subdivision that
causes smaller particles to reunite (1) due
to the mechanical forces involved and (2) by
the attractive force
Dispersion example
 Grinding or wet-milling in
the presence of surfaceactive materials
 Incorporation of
pigments
 Coating masses
 Mustard
 Mayonnaise
 ointment
Dispersion example
 Adding an emulsifying
agent
 Soap in an oil-water
mixture to produce an
emulsion
 Egg yolk in mayonnaise
made of oil and
calamansi juice or
vinegar
Dispersion example
 Peptizing agent: reduces big particles to colloidal size
 Enzymes that break down food particles during the
digestive process
 Homogenizer: machine that emulsifies or blends a substance
 Milk is homogenized to
prevent fat from rising
to the surface
Condensation
 Process of combining molecules in supersaturated solutions
to precipitate or coagulate them in colloidal size
 Examples:
 By exchange of solvent
 By changing physical state
 By controlled condensation
 By Chemical methods: reduction, hydrolysis, oxidation
Purification of Colloidal Solutions
 Ultra-filtration
 Uses ultrafilters
(ordinary filter paper
impregnated with a
solution to make pores
smaller so collloidal
particles cannot pass
through)
Purification of Colloidal Solutions
 Dialysis
 Process of separation of crystalloids from colloids by
diffusion through the animal or vegetable membrane
 Electrodialysis:
carried out in a
direct current field
to accelerate process
of purification
Application of Colloids
 Purification of water
 Impure water is treated with alum, Al3+ ions of alum precipitate
negatively charged clay particles, bacteria, colloidal particles and the
impurities
 Purification of polluted air
 Smoked is negatively charged colloidal suspension consisting of C
particles. Air is passed through precipitator where the charge is
neutralized & C settles down while the hot air passes out through
chimney
Application of Colloid
 Removal of dirt from
sewage
 Sewage contains
charged dirt particles,
which is passed through
tanks fitted with
oppositely charged
electrodes. By
neutralizing the charge,
dirt is coagulated.
Application of Colloid
 Leather tanning
 The raw material skin is
positively charged
colloidal system, which
is treated with negatively
charged colloidal
solution of tannin,
whereby mutual
coagulation of oppositely
charged colloids takes
place.
Application of Colloid
 Laundry
 Soaps in water form colloidal solution, which adsorb greasy
materials, dirt by emulsion formation and
emove dirt from clothes.
 Medicine
 Silverwater/Colloidal Silver
 one of the best infection-pre
-ventative agents, but unfortunately its use was short lived
 sterilize recycled water aboard their space stations
 Colloid Chemistry
Chemical Impact
Sources
• BreakingThrough Chemistry by Baguio, Saranay & Rose Mary
Butaran. 2006
• New Age Engineering Chemistry by Mukhopadhyay, Raghupati &
Sriparna Datta. 2007
• Chemistry 7th ed by Steven Zumdahl & Susan Zumdahl. 2007
Other Helpful Links
 Chemistry of Colloids by Paul Davies:
http://www.chm.bris.ac.uk/webprojects2002/pdavies/
 Colloids: http://www.tutorvista.com/search/colloids
 Colloids:
http://wps.prenhall.com/wps/media/objects/3082/31566
28/blb1306.html