final practice about explanation of colloid

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colloid 

           A.  UNDERSTANDING COLOID

         Colloid is a form of a homogeneous phase-shift mixture (of a kind) to be heterogeneous. The mixture is the state between the solution and the suspension. In macroscopic colloids appear homogeneous, but in fact colloids are classified as heterogeneous mixtures, because the differences in both colloidal phase particles can still be observed and differentiated macroscopically.

Like a sugar solution or a saline solution, the particles may contain more than one molecule but are not large enough to be seen with a regular microscope. The particles located within a distance of colloidal size have a very large surface area compared with the surface area of ​​larger particles of the same volume.

The dispersion system is a system in which a substance is fine or dispersed in another substance. Colloid is a dispersion system, because it consists of two phases, namely the dispersed phase, and the dispersing phase.

B. CHOLOID PROPERTIES

1. Optical properties

Optical properties of colloids are properties that can scatter light. This event is called the Tyndall Effect. In everyday life, this effect can be observed as in a cinema where smoke billows will make the projector light brighter, foggy areas (highlight the lights more clearly), sunlight entering through the gap will make the dust particles appear more clearly.

When light is passed through a medium containing particles less than 10-9 m, the light beam can not be detected from the medium called optically clear. When the colloidal particles are present, however, some of the light will be scattered, and some will be transmitted in low intensity.

The Tyndall effect can be used to observe colloidal particles using a microscope. Because the intensity of light scattering depends on particle size, the Tyndall effect can also be used to estimate the weight of colloid molecules. Colloidal particles of small size, tends to scatter light with short wavelengths. Conversely large colloidal particles tends to scatter light with longer wavelengths

2. Kinetic properties

This property consists of two movements, namely thermal movement and movement due to the force of gravity. Colloid particles move continuously with the movement of a broken or zig-zag known as Brownian motion.

Brown motion occurs due to unbalanced collision of medium molecules against colloidal particles.

Colloidal particles have a tendency to precipitate due to the effects of earth's gravity. It depends on the particle mass density of the medium. If the mass density of the particle is larger than the dispersing medium, then the particle will precipitate. Conversely, if the smaller mass meeting will float.

The solute particles will diffuse from the high concentration solution to the lower concentration areas. Diffusion is closely related to Brownian motion, so it can be considered colloid molecules or particles diffuse due to Brownian motion. Colloidal grains diffuse very slowly because of their relatively large particle size.

3. Physical Properties

The properties of colloidal physics vary depending on the type of colloid. In hydrophobic colloids the properties are density, the surface tension and viscosity are almost identical with the dispersing medium. In hydrophilic colloid due to hydration, the physical properties are very different from the medium. Its viscosity (thickness) is larger and its surface tension is relatively smaller.

4. Electrical Properties

The colloidal particles have their surface charge caused by ionizing or absorbing the charge. When the charged colloidal particles are placed in an electric field, the particle will move toward one electrode depending on its charge, this process is known as electrophoresis.

5. Adsorption Properties

Adsorption is the process of attaching a substance to a solid or liquid surface. Colloidal particles are easy to adsorb color. The size of small colloidal particles so that the surface is large and causes great adsorption ability.

6. Coagulation properties

Coagulation is a clumping of colloidal particles, so the stability of the colloidal system becomes lost. The cause of coagulation in the colloidal system due to the influence of heating, cooling, electrolyte mixing, and electrophoresis that lasts long. Examples of coagulation such as boiling raw eggs in water, cooling hot agar, and purifying river water.

7. Protective Properties

It is a colloidal system added to other colloids, resulting in a stable colloid. Like the addition of gelatin to ice cream, to produce soft ice cream.

    C. TYPES OF KOLOID

Based on the dispersed phase, the colloidal system is divided into 3, ie soles, emulsions, and foams.

• ·         Sol, solid dispersed phase.
• ·           Emulsion, liquid dispersed phase.
• ·           Foam, gas dispersed phase

D. CHOLORY CHARACTERISTICS

• Molecular dispersion
• The nature of the colloidal mixture is heterogeneous.
•  The particle dimension is less than 1 nm, so it needs a special microscope to observe colloids.
•  Although colloids are heterogeneous, colloids can not be filtered. Like seawater that also contains salt therein, but after screening also did not get results.
•  The stable colloidal system is caused by the pulling force (London-van der waals), which causes colloidal particles to converge to aggregate and precipitate. Also due to repulsive force caused by overlapping of electrically charged double layer layers.
• Examples of colloids such as sugar solution, salt solution, alcohol, vinegar, spiritus, sea water, gasoline, and clean air.

E. COLOID UTILIZATION
Colloids are widely used in industry because they do not dissolve the mixture homogeneously, it is stable, and is not easily damaged.

Use of colloids in industry:

1. Cosmetics industry
Many use emulsions and froths, such as foundation, shampoo, facial cleanser, deodorant, and body moisturizer.

2. Textile Industry
Textile dye in the form of soles makes the colors absorb well.

3. Pharmaceutical Industry
Medicines are mostly made in the form of soles.

4. Industrial soaps and detergents
Soaps and detergents are emulsifying dirt and water on clothing that keeps clothes clean

5. Food and beverage industry
Food and beverages such as soy sauce, sauce, milk, mayonnaise, and butter are made in various forms of colloids.

Colloids also have beneficial properties. As :
1. Tyndall effect
In cinemas with clearer lights, lampshades are made of colloids so they can scatter light.

2. Properties of Electrophoresis
Which is used for DNA identification as well as victims of criminals

3. The properties of adsorption
3a. Bleaching cane sugar
The red color of sugar cane is adsorbed by diatomaceous soil, by dissolving the sugar in water, then flowing through the soil of diatoms.

3b. Purifying water
Conducted by adding water with Tawas or aluminum sulfate absorbing water pollutants, activated carbon for very high pollution, add sand as filter, chlorine as desingektan, lime toad increase pH value due to alum use. 

4. Properties of Coagulation
a. Rubber clumping
b. Purifying water
     The mud in the water is coagulated by using alum
c. Disposal of factory smoke
     Before being thrown into the chimney, smoke flows into a high-voltage metal (20-75 kV) so that the surrounding air molecules are ionized. These ions are adsorbed by smoke so smoke has a charge. Then the smoke is pulled by another electrode so that the gases removed are free of smoke.

5. Colloid Protector
a. Emulsifiers such as soap
b. Milk is protected by casein which prevents fat clots
c. Butter is protected by lecithin that prevents fat clots
d. Ice cream is protected by gelatin which prevents the formation of sugar crystals or ice cubes.
e. Ink and paint are protected by silicone oils that make ink and paint last longer.