Colloids

1. Colloids

2. Can you name an example of a colloid?

3. Colloids are mixtures with particles intermediate in size between solutions and suspensions (particle size 1 nm to 1000 nm) • You cannot see the individual particles. • The particles do not separate upon standing . • The particles cannot be separated by a filter.

4. The colloidal particles make up the dispersed phase(solute like phase) and the dispersing medium is the solvent like phase. Like solutions, colloids can be solids, liquids, or gases.

5. Types of Colloids Dispersing Dispersed Colloid Type Example Substance Substance (solute) (solvent) Gas Liquid Aerosol Fog Liquid Gas Foam Whipped Cream Liquid Liquid Emulsion Milk Solid Gas Solid Foam Marshmallow Solid Liquid Solid Emulsion Butter

6. Colloid particles may be so small that the dispersion appears uniform even under a microscope, but the are large enough to scatter light effectively. The scattering of light by colloidal particles is known as the Tyndall effect.

7. The most important colloids are those in which the dispersing medium is water. Colloids can be hydrophilic (water loving) or hydrophobic(water fearing). In the human body, large molecules such as enzymes or antibodies are kept in suspension by interaction with surrounding water molecules. The molecules contain hydrophobic and hydrophilic particles, and the molecules fold in such a way that the water hating colloids are away from the water molecules and the water loving groups are on the surface, interacting with the water molecules.

8. Hydrophobic colloids can be prepared in water only if they are stabilized in some way----usually by placing ions or hydrophilic groups on their surface. These ions or hydrophilic groups interact with the water.