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Colloidal System:    A mixedcombination in which solute particles are greater than molecules or ions butcannot be seen by nude eye is called colloidal solution. Anfamiliar mixture of two substances, one of which, called the dispersed phase,is regularly distributed in a outstandingly divided state through the secondsubstance, called the dispersion medium.    The dispersion medium may be a gas, aliquid, or a solid and the dispersed phase may also be any of these, with the exclusionof one gas in another. A system of liquid or solid   collides dispersed in a gas is calledan aerosol.

Asystem of solid substance or water-insoluble liquid colloids dispersed inliquid water is called a hydrosol.There is no severe line of differentiation between true solutions and colloidalsystems or between mere holdups and colloidal systems. When the particles ofthe dispersed phase are smaller than about 10-3 ?m in diameter,the system begins to assume the assets of a true solution; when the particlesdispersed are much greater than 1 ?m, departure of the dispersed phase from thedispersing medium becomes so rapid that the system is best considered asa suspension.According to the latter criterion, natural clouds in the atmosphere shouldnot be termed aerosols; however, since many cloud formsapparently exhibit features of true colloidal suspensions, this strict physical- chemical definition is often ignored for determinations of expedient andhelpful analogy. Condensationnuclei and many artificial smokes maybe considered as aerosols.The dispersion medium may be a gas, a liquid,or a solid.Smokeis composed of a solid dispersed in gas.

Milk isa liquid dispersed in liquid.Pumicestone is a gas dispersed in solids.Thereare two forms of colloidal systems.Sol:  A system composed of non-viscous colloidalsolution is called sol.

For example milk.Gel:  A system composed of viscid colloidal solutionis called gel. For example butter.

Thecolloidal system can be categorized into two general classes on the basis oftheir empathy for liquids:LyophilicSystem:   The system in which dispersed phase andliquid dispersion medium attaract each other is called lyophilic system.LyophobicSystem:   The system in which the dispersed phase andliquid dispersion phase repel each other is called lyophobic system.   Types of Colloidal Dispersions:   Dispersedphase and dispersion medium can be solid, liquid or gas. Depending upon the stateof dispersed phase and dispersion medium, eight different types of colloidaldispersions can exist.Eight Different Types of ColloidalDispersions 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)    Itis important to note that when one gas is mixed with another gas, a similarmixture is formed i.e. gases are completely miscible into each other. Colloidaldispersions are varied in nature and gas dispersed in another gaseous mediumdoes not form colloidal system.    Whenthe dispersion medium is gas, the solution is called Aerosol and when thedispersion medium is liquid, the colloidal dispersion is known as Sol. Sols canfurther be categorized into different types depending upon the liquid used.

If the liquid used is water, the solution isHydrosol or Aquasol.If liquid used is Benzene, solution is calledBenzosol.If liquid used is Alcohol, the solution is Alcohol.If any organic compound is used, the solutionis  Organosol.Example of ColloidalDispersions.

Different Types of ColloidalDispersion 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  Propertiesof Colloidal System:  The colloidal system shows followingproperties.Adsorption:   The affinity of molecules and ions to followto the surface of certain solids or liquids is called adsorption. Colloidalparticles show a high tendency of adsorption. Thus, colloidal system provideslarge surface area of adsorption of molecules and ions.

BrownianMovements:    Robert Brown in1927 observed that colloidalparticles show random dancing movements. These movements were named Brownianmovements.  TyndallEffect:   Thecolloidal particles scatter light. This called Tyndall Effect. The path oflight seems as a cone.

It is known as Tyndall cone. This goods helps to detectthe presence of colloidal particles.Precipitation:   Theadditions of an electrolyte remove the electrical double layer present aroundthe colloidal particles. As a result the dispersed particles of a colloidalsuspension will combined and precipitous.ElectricalProperties:    All colloidal particles carry same electriccharge. This charge may be positive or negative.

There is adsorption of freeions in the dispersion medium. It produces an electrical double layer aroundthe colloidal particles. The electric charges on the colloidal particles calmdown colloidal system.Filtration:   The colloidal particles cannot pass througha parchment membrane. This goods of colloidal dispersions is used to separatethem from true solution by a process called dialysis.PhaseReversal:   The sol and gel form of colloidal system canbe interchanged due to change in certain conditions.

Certain lyophilic solsform 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. Thisprocess is known as solution. The property of colloidal dispersions is calledphase reversal. Surface Charge:   Themost important characteristic of colloidal systems is surface charge on theparticles.

A particle is a group of bonded atoms or molecules. Chargedparticles repel each other, overpowering the tendency to collective andremaining dispersed.     BiologicalSignificance of Colloidal Systems:   Colloidal have following biologicalsignificance:    Protoplasma colloidal system:     Protoplasm a living, and viscous substance.It is surrounded by cell wall. It is present in prokaryotic and eukaryoticcells. Protoplasm is colloidal in nature. The small molecules and ions are truesolute particles. But the larger particles remains postponed in water and formcolloidal suspension or colloidal solution.

Cyclosisand amboeid movements:    The cyclosis occurs due to phase reversal ofcolloidal property. The cyclosis usually occurs in sol phase. Amoeboid whereaboutsin amoeba occur due to colloidal properties.Fruits:   Fruits store a large amount of protien andstarch. They also exhibit colloidal properties. These properties help in thestorage of food in fruits.

  Blood:     The plasm protein forms a colloidal systemin blood. This system maintains the pH and osmotic concentration of blood.Milk:   Milk is perfect colloidal system. It containsall necessary nutrients for young.The Ultimate Colloid:    Thehighest quality colloidal systems are produced by the electro-colloidal method,meaning the inorganic or organic particles and water have been completelycolloid. This is simultaneous dispersion and bonding by a current sent throughthe combination. This is the only method that will create a true colloidalsystem by manufacture.

Products that are simple mixtures of metal and liquidcannot possess nearly the potential of electro-colloids, and are therefore ofquestionable value. The proper electrical process allows inorganic or organicparticles that are well within the colloidal size range to be drawn off aningot. Animated by Brownian movement, they are able to remain in suspension ina liquid medium almost indefinitely.     Allother things being equal, the number of particles varies inversely according tothe cube of the size change, so if size is reduced 50 percent, overall numberis multiplied by eight. This is a mathematical evidence, and is determined byactual count using an electron microscope and by atomic absorption. Obviously,ideal size is element dependent.

Size is controlled by frequency, amperage andmicro-meshes, among other things.    Theultimate colloidal sol contains ultra-fine and ultra-light particles in therange of 0.015-0.005 microns in diameter, and they will remain up in the air inde-ionized water without need of any other ingredient. There is no visible gatheringof inorganic or organic particles either in the solution or settled on thebottom. Products that show visible particles in the solution or at the bottomof the container indicate that the particles are either too large or have notreceived the proper electrical charge.    The metallic particles in a sol may vary inconcentration, but more is not necessarily better, unless we have correspondinglysmaller particles.

In fact, the reverse is usually true- less is better, and inessence, less is more, functionally speaking, because as noted earlier, thehigher the concentration in a solution, the more likely the attraction forcewill overcome the repelling charge. But even before this happens, effectivenessis reduced. The highest quality colloid will have a certain maximum number ofparticles. They will be of the minimum possible size, and ideally no more thana “handful” of atoms hooked together per molecule of water utilized, and in anegatively charged state. This will prevent further aggregation at that size. Testing a Colloidal System:    A quick way to see if a solution containscolloids is by observing the Tyndall effect.

A clear colloidal dispersion willappear turbid when a sharp and intense beam of light is passed through. Thescattered light also takes on a cone shape within the solution. A simple way toobserve this is to shine a very bright flashlight through a test tube of the dispersionin a dark room.     Acritical indicator of a colloidal system’s quality is its color. The ideal formof colloidal silver, for example, will have a golden yellow color. As the sizeof each particle increases, the color of the suspension continues fromyellow to brown to red to gray to black. Therefore, the color sort could alsobe read as “best to fair to mediocre to inferior.

” In all cases, systemsproduced using the electro-colloidal methods are a different color than thosefrom other methods except where an non-natural dye is used to imitate theproper 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 truecolloidal, examine the ingredients. If it contains an ingredient other than thedesignated colloidal particles, the product may not be suitable.

If noadditional ingredient is listed, but the product requires refrigeration, itmeans there is an ingredient in it that might spoil at room temperature.Properly prepared using the electro-colloidal method, a colloidal systemrequires no such ingredient. Unnecessary to say, a product with instructions toshake before using is also quite unsure. 

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