Suspensions and Colloids Notes

Solutions, Suspensions, and Colloids

Suspensions and colloids are special types of liquids liquids often studied with solutions. solutions. Both are commonly mistaken for solutions, but neither actually is considered to be solutions. A solution is a heterogeneous mixture in which one or more components have a particle size greater than 105 cm (in diameter). Very often these particles are visible to the naked eye. Components of a suspension can  be evenly distributed by a mechanical means, like by stirring the contents, but the components will settle out. Important points about suspensions: 1. dissolved dissolved parti particles cles are usuall usually y “clumps “clumps”” of molecules molecules 2.

particles particles settle settle out out over time to to the bottom bottom of the containe container  r 

3. they they can can be sepa separat rated ed by filtra filtratio tion n 4. are not not transparent transparent (see-throug (see-through)ins h)instead tead they are "murky" or "opaque 5. are not not cons conside idered red to to be “per “perman manent ent”” ex. Sand in water; muddy water; oil and vinegar dressing dressing A colloid is a heterogeneous mixture in which the particle size ranges between 10-7 and 10-5 cm. These  particles are intermediate in size compared to those found in solutions and suspensions, and the particles can  be mixed such that they remain evenly distributed without settling out due to Brownian motion.  Brownian motion (named in honor of the botanist bo tanist Robert Brown) is the random movement of particles suspended in a liquid or gas that allows them to remain suspended even though their mass is enough for  gravity to pull them out of solution.

The mixture this substance forms is called a colloid. A colloidal dispersion consists of colloids in a dispersing medium. Important points about colloids: 1. dissolved dissolved parti particles cles are usuall usually y “clumps “clumps”” of molecules molecules 2. particles don not settle settle out over time to the bottom bottom of the container  3. they cannot be separated by filtration 4. are not always transparent transparent (see-through) often they are are considered "murky" or "opaque" 6. are consid considere ered d to to be “perma “permanent nent”” 7.

Classes of Colloids Class Sol Gel Liquid emulsion Foam Solid aerosol Liquid aerosol Solid emulsion

Phases solid dispersed in liquid solid network extending throughout liquid liquid dispersed in a liquid gas dispersed in liquid solid dispersed in gas liquid dispersed in gas liquid dispersed in solid

Example paints, mud gelatin milk, mayonnaise shaving or whipped cream smoke, car exhaust Fog, mist, clouds, aerosol spray cheese, butter  

Comparative sizes of particles in solutions

Often it is possible to distinguish between a suspension, a co lloid and a true solution using one simple test: shine a light through the substance.

If the substance is a solution, the light will pass straight through it without being seen. If the substance is a colloid, the light will form a visible path through the substance in a phenomenon known as the Tyndall Effect. This Tyndall Effect is caused by reflection of light by very small particles in suspension in a transparent medium. It is often seen from the dust in the air when sunlight comes in through a window, or comes down through holes in clouds. It is seen when headlight beams are visible on foggy nights, and in most X-File episodes when Moulder and Sculley check out some dark da rk place with flashlights. If the substance is a colloid, the larger suspended particles may scatter the light in all directions producing a cloudy appearance.