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Colloids

Colloids . From Greek = “glue” Between suspensions (fine sand in water, mixed up) & solns Have very high molar masses Bio-molecules (starch, protein, nucleic acids) Have large sizes Bio-molecules Tyndall effect  scatter a beam of light Do not settle out like suspensions

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Colloids

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  1. Colloids • From Greek = “glue” • Between suspensions (fine sand in water, mixed up) & solns • Have very high molar masses • Bio-molecules (starch, protein, nucleic acids) • Have large sizes • Bio-molecules • Tyndall effect  scatter a beam of light • Do not settle out like suspensions • Not the same as hemorrhoids

  2. More on colloids • Dispersion of solid substance in fluid medium = sol • Dispersion w/out mobility = gel

  3. Types of colloids • Depend on state of dispersed phase (in least amount) and the dispersing medium (greatest amount)

  4. Liquid/gas Liquid/liquid Solid/gas Solid/liquid Whipped cream Milk & mayo Marshmallow Butter Dispersing Medium/Dispersed Phase

  5. Curds • Coagulation can be instigated • By introducing ions into dispersing medium • Milk • Milk contains colloidal suspensions of proteins (casein) w/hydrophobic cores • Upon fermentation, lactose  lactic acid • Lactic acid  proton plus lactate ion • Charges on colloidal surfaces overcome • Coagulates  “curds” • Similar process used in adding metal ions to take out soil particles

  6. Hydrophilic colloids • Starch • Proteins • Milk • Demo

  7. Emulsions • Colloidal dispersions of one liquid in another • Mayo, milk • Liquids of different polarities are immiscible • Need emulsifying agent • Such as soap (one polar end, one non-polar) & proteins • In food items  soy lecithin • In the world of cleaning  surfacants (soaps, etc.)

  8. Surfacants • NaOH + animal or veggie fat  Na+ fatty acid- • The fatty acid has a long non-polar tail and a very polar group • Can be used to take away (clean) non-polar entities like oil, dirt • Surfacant (soap) used in cleaning = detergent

  9. Detergents • Lower surface tension of water (disrupts H-bonding) • This enhances action of detergent • Let’s watch the following video: • http://www.ilpi.com/genchem/demo/tension/#demo

  10. Two common detergents • Sodium laureth sulfate • Sodium lauryl sulfate

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