Since Colligative Strength depends on the # of particles in solution, it can often be determined from its van't Hoff/ionization factor (i)!
Unlike molarity, MOLALITY is independent of temperature and pressure! (Only one purpose: to have units of moles per kg)
MOLALITY = MOLES solute / KG solvent!!! Do not screw up!
Molarity always SLIGHTLY LOWER than Molality (because denominator contains BOTH the solute & the solvent)
VAPOR PRESSURE
- As temperature increases, vapor pressure increases
- The weaker a substance's intermolecular force (IMF), less energy need to leave the liquid, and thus HIGHER the vapor pressure/more easily it evaporates (ex: diethyl ether vs. H2O: see below)
- thus, HIGHER the Vapor Pressure, LOWER the Boiling Point! (also see below)
1) VAPOR PRESSURE DEPRESSION
http://www.youtube.com/watch?v=0ZwknpcwTyQ
Adding more solute to a solution will DECREASE its Vapor Pressure
WHAT you put in solution and HOW MUCH you put into solution will affect changes to Vapor Pressure (count "molal", ex: C6H12O6, NaCl, CaCl2)
ex: Adding salt to boiling water:
- actually going to take a LONGER time to boil (since the vapor pressure has been depressed, takes for heat and time to reach the solution's boiling point)
- BUT, more HOT water molecules, bound to the solute particles, will STAY in the liquid phase INSTEAD of jumping to the gas/vapor phase, so the "pasta" will COOK FASTER!
- High vapor pressure out by beach (humid atmosphere), Low vapor pressure where dry at high altitudes (Not humid atmosphere)
ex: Adding salt to boiling water:
- actually going to take a LONGER time to boil (since the vapor pressure has been depressed, takes for heat and time to reach the solution's boiling point)
- BUT, more HOT water molecules, bound to the solute particles, will STAY in the liquid phase INSTEAD of jumping to the gas/vapor phase, so the "pasta" will COOK FASTER!
- High vapor pressure out by beach (humid atmosphere), Low vapor pressure where dry at high altitudes (Not humid atmosphere)
2) BOILING POINT ELEVATION
Boiling point when Vapor Pressure = Atmospheric Pressure
Boiling Point DECREASES with altitude (ex: 100°C in New York, 69°C on Mt. Everest)
- boils faster, but takes longer to cook because not hot enough!
For every mole solute in kg solvent, the BP is raised by a certain amount ---> BP is proportional to the MOLALITY of a solution
***but remember that molality (m) is independent of temp. and pressure...
...
RAOULT'S LAW
Sweet chem dude again :) http://www.youtube.com/watch?v=PKgpumIUfyk
"Raoult's Law Graphs: LINEAR addition of partial pressures (concentration of gases) dependent on changing mole fractions. (No bendy lines)"
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