MIXTURES AND DISSOLVING. CE/Honors Chemistry Unit 10

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1 MIXTURES AND DISSOLVING CE/Honors Chemistry Unit 10

2 TYPES OF MIXTURES Solution: homogeneous mixture of two or more substances in a single phase Two parts: solvent (greater amt) and solute Does not separate on standing Cannot be separated by filtration Many types of solutions (p. 81)

3 TYPES OF MIXTURES Suspension: heterogeneous mixture that must be stirred to keep mixed Particles settle out Particles over 1000 nm Can be separated by filtration Not transparent

4 TYPES OF MIXTURES Colloid: heterogeneous mixture with particles of intermediate size Two parts: continuous and dispersed phases Particles do not settle out Particles between nm Can be separated by a semipermeable membrane but not normal filtration

5 CLASSES OF COLLOIDS Sol: solid in liquid (paint, mud) Gel: solid network in liquid (gelatin, pearls, opals) Emulsion: liquid in liquid or solid (milk, mayonnaise, cheese) Foam: gas in liquid or solid (whipped cream, marshmallow) Aerosol: liquid or solid in gas (fog, smoke, cloud, anything in spray can)

6 TYNDALL EFFECT Scattering of light by colloid particles Colloids/Sunset Demo (Journal)

7 THE SOLUTION PROCESS Factors Affecting Rate of Dissolving: Crushing or breaking up: increases the surface area exposed to the solvent Stirring or agitating the solution: brings fresh solvent into contact with the solute particles Heating: faster motion gives more collisions with more energy which helps separate particles from each other and disperse them in the solvent

8 SOLUBILITY There is a limit to how much solute can be dissolved in a certain amount of solvent. This limit is expressed as solubility (g/100 ml solvent). Solution equilibrium occurs when the rates of dissolving and crystallization are equal

9 SOLUTION CONDITIONS Saturated solution: contains the maximum amount of dissolved solute. Unsaturated solution: contains less than the maximum amount of dissolved solute. Supersaturated solution: contains more solute than a saturated solution under the same conditions. (Created from a saturated solution at a higher temperature that cools without forming crystals.)

10 SOLUTION TEST A solution at room temperature has no crystals in it. How can we know if it is saturated, unsaturated, or supersaturated? TEST: Add more solute and observe the results. Crystal dissolves: unsaturated Crystal drops to bottom and remains unchanged: saturated Crystal drops to bottom and grows substantially: supersaturated

11 DISSOLVING IONIC COMPOUNDS IN WATER Dissolving in Water Hydration occurs between water and ionic solutes. The water molecules are attracted to the ions and draw them away from the surface of the crystal. The ions are surrounded by water molecules. New ions are exposed and the process repeats, resulting in the dissolving of the entire crystal.

12 DISSOLVING IONIC COMPOUNDS

13 DISSOLVING MOLECULES Molecules get surrounded by water without breaking up.

14 COMPARISON OF IONIC AND COVALENT DISSOLUTION Draw pictures similar to the following in your notes: Ionic Covalent

15 SOLUTE-SOLVENT INTERACTIONS Like Dissolves Like (similarly charged) Polar solvents dissolve polar (or ionic) solutes. Nonpolar solvents dissolve nonpolar solutes. Liquid solutes and solvents that are not soluble in each other are immiscible. Liquids that dissolve in each other are miscible.

16 MISCIBLE SOLUTIONS

17 DISSOLVING EFFECTS Pressure Only affects gas solubility Henry s Law: the solubility of a gas is directly proportional to the partial pressure of the gas on the liquid s surface. Examples of Henry s Law: Carbonated beverages (bottled under pressure) The Bends experienced by divers (more gases dissolve in blood in deep water, when rising the gas comes out as bubbles and go to brain)

18 DISSOLVING EFFECTS Heats (enthalpy) of Solution is H Energy change (heat absorbed or released) when dissolving takes place Solid in liquid: Usually endothermic, H sol is positive, requires energy (colder) Sometimes exothermic, H sol is negative, gives off energy (warmer) Most become more soluble if temperature is raised Gas in liquid: Exothermic Becomes more soluble at lower temperatures fish die in warm water (not enough oxygen); thermal pollution