MIXTURES AND DISSOLVING General Chemistry Unit 10.
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Transcript of MIXTURES AND DISSOLVING General Chemistry Unit 10.
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)