COLLOIDS AND EMULSIONS

INTRODUCTION A colloid is a suspension in which the particles are permanently suspended. Colloids can be mixtures of different phases of matter. Some examples would be glass, a solid in a solid, paint, a solid in a liquid, fog, a liquid in a gas, milk, a liquid in a liquid, smoke, a solid in a gas.

INTRODUCTION The particles in a colloid are not as small as the particles in a solution. They are smaller than the particles in an ordinary suspension. They cannot be seen with an ordinary microscope. A colloid can’t be separated by using a porous filter paper. The colloid will pass right through.

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INTRODUCTION Colloid particles are constantly moving. There is no emulsifying agent keeping them in suspension, so they are constantly bumping into other particles. In fog, the particles of water in the air keep bumping into the air molecules. These collisions keep the particles from settling out of the colloid.

INTRODUCTION This movement also explains why a light beam is scattered when shined through a colloid. The light strikes the moving particles and is scattered, or spread out. The cloudy appearance of a colloid is caused by the scattering of light. This scattering is called the Tyndall effect.

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INTRODUCTION An emulsion is a type of colloid. When a liquid is suspended in another liquid, the result is an emulsion. Milk and paint are examples of emulsions. There are both temporary and permanent emulsions. Vinegar and oil when mixed together make a temporary emulsion.

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INTRODUCTION Homogenized milk would be an example of a permanent emulsion. In a permanent emulsion the particles are very small, too small to be filtered out. Since the particles are so small, they will stay in suspension permanently.

INTRODUCTION Many detergents or other cleaning products contain emulsifying agents. An emulsifying agent keeps an emulsion from separating. Dirt and grease are broken apart by the detergent, and the emulsifying agent makes them a permanent part of the water and they are washed away with the water.

INTRODUCTION Other familiar emulsifying agents would be gelatin and egg yolks. These are usually added to food to keep ingredients from separating.

OBJECTIVES Describe and give examples of an emulsion. Describe and give examples of a colloid.

IN QUESTION You mix a glass of instant tea using 2 tablespoons of mix in 16 ounces of water. You let the mixture stand for 2 days. Will the mixture separate after 2 days? Explain. No, it becomes a solution, it is clear.

VOCABULARY Emulsion – a suspension of two liquids. Homogenization – a formation of a permanent emulsion. Colloid – a suspension in which the particles are permanently suspended. Tyndall effect – scattering of light by particles of a colloid.

NOTES Colloid particles are not as small as particles in a solution. Colloids are cloudy looking. Particles are constantly in motion. Colloids can’t be filtered. Colloids can be mixtures of different phases of matter.

NOTES Common colloids Fog Paint Homogenized Milk Glass Smoke

NOTES 2 kinds of emulsions: Permanent Homogenized milk Temporary Vinegar and oil dressing

NOTES Particles in a permanent emulsion are smaller than particles in a temporary emulsion. Particles in a permanent emulsion can’t be filtered.

NOTES Common emulsions: Raw Milk Butter Cold Cream Mayonnaise Hot Dogs

NOTES Emulsifying agents keep emulsions from separating. Detergents have emulsifying agents. Breaks dirt and oil into tiny particles. Keeps dirt and oil trapped in the water so they wash away.

OUT QUESTION How is a colloid like a solution? How is it different? Like – both are mixtures. Unlike – particles are different sizes.