12.7 – NOTES Heterogeneous Mixtures

IV. Heterogeneous Mixtures Suspensions - mixtures do NOT undergo a chemical change; mixture in which large particles will eventually settle out Cornstarch and water, OJ with pulp, Italian salad dressing; can separate using a filter thixotropic – suspension when stirred will flow, but quickly thickens to solidlike state; house paint; corn starch and water

Emulsion – special suspension occurs b/t two liquids Miscible: when two liquids are soluble in each other; alcohol and water; Immiscible: when two liquids are not soluble in each other; oil and water; Emulsifying agent: chemical substance that coats the surface of droplets of one liquid so that they can remain dispersed throughout a second liquid (eg margarine or ice cream) forming a stable emulsion.

B. Colloids particles larger than solvated particles, but smaller than suspended particles; remain permanently suspended; cannot be separated by filtration or settling;

Brownian motion - erratic movement of colloidal particles - results from collisions of particles of the dispersion medium with the dispersed particles - prevents the colloid from settling - dispersed particles do not settle out b/c charged groups on the surface are attracted to the charged groups of the medium - creates electrostatic layers that repel each other forcing the particles to remain suspended - heat can disrupt the colloid;

Tyndall effect dilute colloids appear to be homogenous, but particles will scatter light; positive Tyndall effect – presence of colloidal particles, light is scattered