MIXTURES AND DISSOLVINGGeneral Chemistry Unit 10

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)

TYPES OF MIXURES

Suspension: heterogeneous mixture that must be stirred to keep mixed

Particles settle out Particles over 1000 nm Can be separated by filtration Not transparent

TYPES OF MIXTURES

Colloid: heterogeneous mixture with particles of intermediate size

Two parts: continuous and dispersed phases

Particles do not settle out Particles between 1-1000 nm Can be separated by a semipermeable

membrane but not normal filtration

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)

TYNDALL EFFECT

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

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

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

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.)

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

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.

SOLUTE-SOLVENT INTERACTIONS

Like Dissolves Like 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.

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, when rising come out as bubbles and go to brain)

DISSOLVING EFFECTS Heats of Solution Energy change (heat absorbed or released)

when dissolving takes place Solid in liquid: Usually endothermic, positive value, requires energy Sometimes exothermic, negative value, gives off energy 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)