Colloids

Matter Pure Substances CompoundsOrganicInorganicElementsMixturesHomogeneousSolutionUnsaturatedSaturatedSupersaturatedHeterogeneousColloids

Mixtures Not every mixture allows particles to dissolve In colloidal dispersion, particles of one substance are distributed (or dispersed) in another substance without dissolving

Colloidal Dispersions Homogeneous mixtures that are not true solutions Particles are relatively large large molecules or clusters of molecules

Phases 2 substances may be a combination of any of these phases: solid, liquid, gas Examples: Italian salad dressing: liquid dispersed in liquid (vinegar and oil) Beaten egg white: gas is dispersed in liquid Gravy: solid in liquid Baked custard: liquid in solid

Term Review Dispersed phase: substance that is dispersed within another Continuous phase: substance that extends throughout the system and surrounds the dispersed phase (ex. Water)

How do colloids stay dispersed? 1. The motion of the molecules in continuous phase Smaller the mass, the faster the speed Smaller molecules in continuous phase move faster than colloids; they collide Collisions change direction of both molecules = keeps colloids dispersed

How do colloids stay dispersed? 2. Colloids are usually molecules of the same substance = have the same charge Like charges repel – push away from each other Water molecules align around colloids and form cushions Prevents the colloids from sticking together and settling

Colloids vs. Solutes Colloids 1000x larger Do not dissolve No impact on freezing/boiling points Bend/reflect light onto another path (Tyndall Effect) Solutes 1 nanometer-1 micrometer Dissolve in other substances Have impact on boiling/freezing points Too small to bend light

Tyndall Effect

Milk Is a colloidal dispersion and a solution Made up of water, lactose, mineral salts, protein, fats Solutes: lactose and mineral salts Colloids: proteins Water, salt, lactose = solution that is continuous phase which protein is dispersed

2 types of colloids Foams Emulsions

Matter Pure Substances CompoundsOrganicInorganicElementsMixturesHomogeneousSolutionUnsaturatedSaturatedSupersaturatedHeterogeneousColloidsFoamEmulsion

Foams Dispersions of gas in liquid Ex. Egg foam: egg white is the continuous phase and air beaten into the white is the dispersed phase Ex. Whipped cream: air is beaten into the cream Not all liquids can make a foam; the more viscous (resistant to flow) the better the foam Viscosity of the fat is greater when cooled – chill cream, bowl, beaters Addition of solutes can alter foam stability (ex. Sugar)

Whipped Cream 1 cup heavy cream 2 teaspoon vanilla 4 tablespoons powdered sugar In a large bowl, whip cream until soft peaks are just about to form. Beat in vanilla and sugar until stiff peaks form. Make sure not to over-beat, cream will then become lumpy and butter-like. **Works best if bowl and beaters are chilled first.

Review Clip

One type of colloidal dispersion A mixture of 2 liquids that do not normally blend with each other Because they can’t combine = immiscible liquids 2 types: Oil in water Mayo, salad dressings, ice cream, cake batters Water in oil Butter and margarine Emulsions

agitation (stirring/beating) stabilizes mixture As mixture is agitated oil breaks into tiny droplets emulsifier is added and coats the droplets so they can not rejoin How are immiscible liquids combined?

Two ends: Usually has an end that dissolves in water (polar) and one that dissolves in fat (nonpolar) What is an emulsifier?

Egg yolk Contains the phospholipid lecithin (good for oil in water) Honey Mustard Starch Used for gravies and sauces Must be heated for a long time Emulsifiers in Foods

Good Eats Questions – Answer in your notebooks 1.Draw a picture of an emulsifier. 2.Why is lecithin important? 3.Describe the steps to make mayonnaise. 4. Why is mustard important? 5.Which foods use mayonnaise as a base?

1/4 teaspoon dry mustard powder 1/8 teaspoon salt 1 egg (pasteurized) 1 tablespoon white vinegar 1 cup vegetable oil In a food processor, combine the mustard powder, salt, egg, and vinegar. Mix until well blended. Gradually drizzle in the oil. Cover and store in the refrigerator for up to two weeks. Mayonnaise