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SUSPENSIONS AND COLLOIDS

==>> For more on Mixtures (Solutions, Suspensions, Emulsions, Colloids )

Suspensions

A suspension is a mixture between two substances, one of which is finely divided and dispersed in the other. Common suspensions include sand in water, dust in air, and droplets of oil in air. Particles in a suspension are larger than those in a solutions; they are visible under a microscope and can often be seen with the naked eye. Particles in a suspension will settle out if the suspension is allowed to stand undisturbed. Many particles of a suspension can be separated through a filter. An example of a simple suspension would be flour in water, or sand in water.

Colloids

A colloid is a type of mixture intermediate between a homogeneous mixture (also called a solution) and a heterogeneous mixture with properties also intermediate between the two.

The particles in a colloid can be solid, liquid or bubbles of gas. The medium that they are suspended in can be a solid, liquid or gas (although gas colloids cannot be suspended in gas).The particles are approximately 10 to 10,000 angstroms in size and generally cannot be filtered, or settled out in an easy manner. Colloids may be colored or translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid. Colloid particles may be seen in a beam of light such as dust in air in a "shaft" of sunlight.

Brownian movement may be used to distinguish between solutions and colloids. Brownian motion is the random movement of colloidal particles suspended in a liquid or gas, caused by collisions with molecules of the surrounding medium. The particles in solutions and colloids are in constant motion. However colloid particles are large enough to be observed and are small enough to still be affect by the random molecular collisions. Colloid particles resist settling rapidly to the bottom of a vessel due to Brownian motion.

Emulsions are a type of colloid

Emulsions are an example of colloids composed of tiny particles suspended in another immiscible (unmixable) material. An emulsion is a suspension of two liquids that usually do not mix together. These liquids that do not mix are said to be immiscible. An example would be oil and water. If you mix oil and water and shake them a cloudy suspension is formed. Let the mixture rest and the oil and water will separate.

An emulsifying agent (emulsifier) is any substance that keeps the parts of an emulsion mixed together. For example if we mix oil and water a suspension will form that over time separates. But now, if we add a few drops and shake the mixture the oil and water will stay mixed much longer.

Examples of emulsions include butter and margarine, and mayonnaise.

Examples of Colloids

Dispersed Medium
Gas
Liquid
Solid
Continuous MediumGas
NONE
(All gases are soluble)
Liquid Aerosol
Examples: Fog, Mist
Solid Aerosol
Examples: smoke, dust
LiquidFoam
Examples: Whipped cream
Emulsion
Examples: Milk, Mayonnaise, hand cream
Sol
Examples: Paint, pigmented ink, blood, Milk of Magnesia
SolidSolid Foam
Examples: Aerogel, Styrofoam, pumice
Gel
Examples: Gelatin, cheese
Solid Sol
Examples: ruby glass

 

Assessment Questions:

Multiple Choice Questions

1. What factor distinguishes a suspension from a colloid?
a) light reflects off the particles of a suspension
b) the particles of a suspension will sink out if left over time to rest
c) suspensions are clear
d) suspensions cannot be filtered

2. An example of an emulsifying agent would be__
a) oil
b) soap

c) water
d) salt

3. An example of a homogeneous mixture is___
a) sand and water
b) flour and water
c) salt dissolved in water
d) oil and water

4. Which statement is not true.
a) particles in a colloid will reflect light
b) the particles of a solution are molecule in size
c) a suspension can be filtered
d) a solution can be filtered

5. Which statement is true about Brownian motion ___
a) Brownian motion is caused by collisions with molecules of the surrounding medium
b) Brownian motion is the random movement of colloid particles

c) Brownian motion may be used to distinguish between solutions and colloids
d) all of the above


 

==>> For more on Mixtures (Solutions, Suspensions, Emulsions, Colloids )


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