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ElectrolytesIonic compounds
Break down into positive and negative ions
Conduct electricity
Essential to us !!!
Strong vs. Weak Electrolytes
Weak—electrolytes partially breaking down in a solution
Strong—electrolytes completely breaking down in a solution
What are colligative properties?
Physical properties
Based on # of solute particles, NOT identity!!!
4 properties1) Vapor Pressure Lowering
2) Freezing Point Depression
3) Boiling Point Elevation
4) Osmotic Pressure
1) Vapor Pressure Lowering
Nonvolatile vs. volatile chemicals Nonvolatile
Not likely to be a gasTakes awhile for gas particles to evaporate
Volatile Gas particles evaporate quickly
Vapor PressurePressure exerted from gas molecules on a liquidCharacteristic of a liquid
Volatile vs. Nonvolatile Liquids
1) Volatile LiquidsWEAK intermolecular forcesHigh vapor pressureEx. Gasoline, alcohols, “Whoosh Bottle”
2) Nonvolatile Liquids STRONG intermolecular forces Low vapor pressure
More Vapor Pressure….
INCREASED vapor pressurePure solvent Particles can easily move between the liquid and
gas phase to create an equal amount of particles in each phase (equilibrium)
DECREASED vapor pressure Solvent + soluteNumber of particles in the solution is increasedLess water/solvent can evaporate
2) Freezing Point Depression
“difference between freezing point of a pure solvent and a solution containing a nonelectrolyte.”
Difference between Freezing point of pure solvent ANDFreezing point of solvent + solute/substance
**Adding a solute/substance LOWERS the freezing point.
3) Boiling Point Elevation
Boiling point— Temperature where a liquid’s vapor pressure = atmosphere
pressure
**Boiling point changes result from changes in vapor pressure.
“difference between boiling point of a pure solvent and a solution containing a nonelectrolyte”
Difference between Boiling point of pure solvent AND Boiling point of solvent + solute/substance
Boiling Point and Vapor Pressure
Substances with low vapor pressureMore energy needed for vapor pressure =
atmospheric pressure SOBoiling point INCREASES
** Solutes in a solution LOWER vapor pressure so boiling point INCREASES !
Osmosis
Semipermeable membraneMembrane selects what particles can go through
and blocks other particles
Movement of water through a semipermeable membraneBased on solute concentration (HighLow solute
concentration)
4) Osmotic Pressure
Pressure exerted by solute particles resisting osmosis
INCREASE osmotic pressureHigh solute concentrationWater drawn in
DECREASE osmotic pressure Low solute concentrationWater driven out
Electrolytes and Colligative Properties
Electrolytes GREATLY influence colligative properties. Electrolytes---dissociate into ions in solution Ions increase the NUMBER of solute particles in a
solvent.