Colloidal second substance, called the dispersion medium. The dispersion

Colloidal System:

    A mixed
combination in which solute particles are greater than molecules or ions but
cannot be seen by nude eye is called colloidal solution. An
familiar mixture of two substances, one of which, called the dispersed phase,
is regularly distributed in a outstandingly divided state through the second
substance, called the dispersion medium.

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    The dispersion medium may be a gas, a
liquid, or a solid and the dispersed phase may also be any of these, with the exclusion
of one gas in another. A system of liquid or solid   collides dispersed in a gas is called
an aerosol. A
system of solid substance or water-insoluble liquid colloids dispersed in
liquid water is called a hydrosol.
There is no severe line of differentiation between true solutions and colloidal
systems or between mere holdups and colloidal systems. When the particles of
the dispersed phase are smaller than about 10-3 ?m in diameter,
the system begins to assume the assets of a true solution; when the particles
dispersed are much greater than 1 ?m, departure of the dispersed phase from the
dispersing medium becomes so rapid that the system is best considered as
a suspension.
According to the latter criterion, natural clouds in the atmosphere should
not be termed aerosols; however, since many cloud forms
apparently exhibit features of true colloidal suspensions, this strict physical
– chemical definition is often ignored for determinations of expedient and
helpful analogy. Condensation
nuclei and many artificial smokes may
be considered as aerosols.

The dispersion medium may be a gas, a liquid,
or a solid.

Smoke
is composed of a solid dispersed in gas.

Milk is
a liquid dispersed in liquid.

Pumice
stone is a gas dispersed in solids.

There
are two forms of colloidal systems.

Sol:  A system composed of non-viscous colloidal
solution is called sol. For example milk.

Gel:  A system composed of viscid colloidal solution
is called gel. For example butter.

The
colloidal system can be categorized into two general classes on the basis of
their empathy for liquids:

Lyophilic
System:

  The system in which dispersed phase and
liquid dispersion medium attaract each other is called lyophilic system.

Lyophobic
System:

  The system in which the dispersed phase and
liquid dispersion phase repel each other is called lyophobic system. 

 

Types of Colloidal Dispersions:

   Dispersed
phase and dispersion medium can be solid, liquid or gas. Depending upon the state
of dispersed phase and dispersion medium, eight different types of colloidal
dispersions can exist.

Eight Different Types of Colloidal
Dispersions are:

.Foam         
.Solid foam              .Liquid                   .Aerosol  Emulsions  

.Gels   
   .Solid 
 .Aerosol   Sol   
  .Solid sol

 

Dispersed Phase

Dispersion Medium

Type of Colloidal Dispersions

Gas

Liquid

Foam

Gas

Solid

Solid foam

Gas

Gas

Does not exist

Liquid

Gas

Liquid Aerosol

Liquid

Liquid

Emulsions

Liquid

Solid

Gel

Solid

Gas

Solid Aerosol

Solid

Liquid

Sol or Colloidal Suspension

Solid

Solid

Solid sol (solid suspension)

   It
is important to note that when one gas is mixed with another gas, a similar
mixture is formed i.e. gases are completely miscible into each other. Colloidal
dispersions are varied in nature and gas dispersed in another gaseous medium
does not form colloidal system.

    When
the dispersion medium is gas, the solution is called Aerosol and when the
dispersion medium is liquid, the colloidal dispersion is known as Sol. Sols can
further be categorized into different types depending upon the liquid used.

If the liquid used is water, the solution is
Hydrosol or Aquasol.

If liquid used is Benzene, solution is called
Benzosol.

If liquid used is Alcohol, the solution is Alcohol.

If any organic compound is used, the solution
is  Organosol.

Example of Colloidal
Dispersions.

Different Types of Colloidal
Dispersion and their examples are summarized in table below:

Type of Colloidal Dispersions

Examples

Foam

Soap, beer, lemonade

Solid foam

Pumice stone

Does not exist

Liquid Aerosol

Fog, dust

Emulsions

Milk, rubber

Gel

Butter, Cheese

Solid Aerosol

Dust

Sol or Colloidal Suspension

Paste, ink

Solid sol(solid suspension)

Pearls, gem stones

 

Properties
of Colloidal System:

  The colloidal system shows following
properties.

Adsorption:

  The affinity of molecules and ions to follow
to the surface of certain solids or liquids is called adsorption. Colloidal
particles show a high tendency of adsorption. Thus, colloidal system provides
large surface area of adsorption of molecules and ions.

Brownian
Movements:

    Robert Brown in1927 observed that colloidal
particles show random dancing movements. These movements were named Brownian
movements.

 

 

Tyndall
Effect:

   The
colloidal particles scatter light. This called Tyndall Effect. The path of
light seems as a cone. It is known as Tyndall cone. This goods helps to detect
the presence of colloidal particles.

Precipitation:

   The
additions of an electrolyte remove the electrical double layer present around
the colloidal particles. As a result the dispersed particles of a colloidal
suspension will combined and precipitous.

Electrical
Properties:

   All colloidal particles carry same electric
charge. This charge may be positive or negative. There is adsorption of free
ions in the dispersion medium. It produces an electrical double layer around
the colloidal particles. The electric charges on the colloidal particles calm
down colloidal system.

Filtration:

   The colloidal particles cannot pass through
a parchment membrane. This goods of colloidal dispersions is used to separate
them from true solution by a process called dialysis.

Phase
Reversal:

  The sol and gel form of colloidal system can
be interchanged due to change in certain conditions. Certain lyophilic sols
form gel under certain conditions. For example, aqueous agar sols are cooled.
It forms a jelly—like gel. The conversion of a sol to a gel is called gelation.
If a gel of gelation or agar is heated, it will convert back to a sol. This
process is known as solution. The property of colloidal dispersions is called
phase reversal.

 

Surface Charge:

   The
most important characteristic of colloidal systems is surface charge on the
particles. A particle is a group of bonded atoms or molecules. Charged
particles repel each other, overpowering the tendency to collective and
remaining dispersed.  

  

Biological
Significance of Colloidal Systems:

   Colloidal have following biological
significance:

    Protoplasm
a colloidal system:

    Protoplasm a living, and viscous substance.
It is surrounded by cell wall. It is present in prokaryotic and eukaryotic
cells. Protoplasm is colloidal in nature. The small molecules and ions are true
solute particles. But the larger particles remains postponed in water and form
colloidal suspension or colloidal solution.

Cyclosis
and amboeid movements:

   The cyclosis occurs due to phase reversal of
colloidal property. The cyclosis usually occurs in sol phase. Amoeboid whereabouts
in amoeba occur due to colloidal properties.

Fruits:

   Fruits store a large amount of protien and
starch. They also exhibit colloidal properties. These properties help in the
storage of food in fruits.

 

 

Blood:

    The plasm protein forms a colloidal system
in blood. This system maintains the pH and osmotic concentration of blood.

Milk:

  Milk is perfect colloidal system. It contains
all necessary nutrients for young.

The Ultimate Colloid:

    The
highest quality colloidal systems are produced by the electro-colloidal method,
meaning the inorganic or organic particles and water have been completely
colloid. This is simultaneous dispersion and bonding by a current sent through
the combination. This is the only method that will create a true colloidal
system by manufacture. Products that are simple mixtures of metal and liquid
cannot possess nearly the potential of electro-colloids, and are therefore of
questionable value. The proper electrical process allows inorganic or organic
particles that are well within the colloidal size range to be drawn off an
ingot. Animated by Brownian movement, they are able to remain in suspension in
a liquid medium almost indefinitely.

     All
other things being equal, the number of particles varies inversely according to
the cube of the size change, so if size is reduced 50 percent, overall number
is multiplied by eight. This is a mathematical evidence, and is determined by
actual count using an electron microscope and by atomic absorption. Obviously,
ideal size is element dependent. Size is controlled by frequency, amperage and
micro-meshes, among other things.

    The
ultimate colloidal sol contains ultra-fine and ultra-light particles in the
range of 0.015-0.005 microns in diameter, and they will remain up in the air in
de-ionized water without need of any other ingredient. There is no visible gathering
of inorganic or organic particles either in the solution or settled on the
bottom. Products that show visible particles in the solution or at the bottom
of the container indicate that the particles are either too large or have not
received the proper electrical charge.

    The metallic particles in a sol may vary in
concentration, but more is not necessarily better, unless we have correspondingly
smaller particles. In fact, the reverse is usually true- less is better, and in
essence, less is more, functionally speaking, because as noted earlier, the
higher the concentration in a solution, the more likely the attraction force
will overcome the repelling charge. But even before this happens, effectiveness
is reduced. The highest quality colloid will have a certain maximum number of
particles. They will be of the minimum possible size, and ideally no more than
a “handful” of atoms hooked together per molecule of water utilized, and in a
negatively charged state. This will prevent further aggregation at that size.

 

Testing a Colloidal System:

    A quick way to see if a solution contains
colloids is by observing the Tyndall effect. A clear colloidal dispersion will
appear turbid when a sharp and intense beam of light is passed through. The
scattered light also takes on a cone shape within the solution. A simple way to
observe this is to shine a very bright flashlight through a test tube of the dispersion
in a dark room.

 

 

   A
critical indicator of a colloidal system’s quality is its color. The ideal form
of colloidal silver, for example, will have a golden yellow color. As the size
of each particle increases, the color of the suspension continues from
yellow to brown to red to gray to black. Therefore, the color sort could also
be read as “best to fair to mediocre to inferior.” In all cases, systems
produced using the electro-colloidal methods are a different color than those
from other methods except where an non-natural dye is used to imitate the
proper color. Additionally, color varies with concentration, use of a preservative,
and the presence or absence of other trace elements.

    To confirm that a product is a true
colloidal, examine the ingredients. If it contains an ingredient other than the
designated colloidal particles, the product may not be suitable. If no
additional ingredient is listed, but the product requires refrigeration, it
means there is an ingredient in it that might spoil at room temperature.
Properly prepared using the electro-colloidal method, a colloidal system
requires no such ingredient. Unnecessary to say, a product with instructions to
shake before using is also quite unsure.

 

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