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

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

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

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

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

Hydrophilic colloids  Starch  Proteins  Milk  Demo

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.)

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

Detergents  Lower surface tension of water (disrupts H-bonding)  This enhances action of detergent  Let’s watch the following video:  on/#demo on/#demo on/#demo

Two common detergents  Sodium laureth sulfate  Sodium lauryl sulfate