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  • 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

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