Prepared by
Prof. Odyssa Natividad RM. Molo
COLLOIDS
CONTENT
• History
• Components
• Classification
• Properties
• Preparation
• Purification
• Applications
• 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 & lyophobicLYOPHILIC 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) Smoke particles pick
up a negative charge.
2) Smoke particles are
attracted to the
collecting plates.
3) 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 surface-
active 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
