Chem 1220; Lecture 4 Flashcards
(16 cards)
What is vapor pressure?
he pressure exerted by vapor when it is in equilibrium with the liquid (equilibrium of vaporization and condensation)
What is a volatile substance?
A substance that has a measurable vapor pressure
What is Raoult’s Law?
The vapor pressure of a solution equals the vapor pressure of the pure solvent multiplied by its mole fraction (P = χsolventP°)
For a mixture of two volatile components A and B, what is the total vapor pressure?
Ptotal = PA + PB = χAP°A + χBP°B
What are the four colligative properties?
- Vapor pressure lowering
- Boiling point elevation
- Freezing point depression
- Osmotic pressure
What is special about colligative properties?
They depend on the collective effect of the number of solute particles, not on the identity of the particles
What is the formula for boiling point elevation?
ΔTb = Tb(solution) - Tb(solvent) = iKbm
What is the formula for freezing point depression?
ΔTf = Tf(solution) - Tf(solvent) = -iKfm
What is the van’t Hoff factor (i)?
The number of particles produced when a compound dissociates in solution
What is the van’t Hoff factor for these compounds?
- KBr: i = 2
- MgSO4: i = 2
- CaCl2: i = 3
- Sucrose: i = 1
What is a semipermeable membrane?
A material that allows only certain ions and small molecules to pass through their network of tiny pores
What is osmosis?
The net movement of solvent molecules through a semipermeable membrane from a region of higher solvent concentration to a region of lower solvent concentration
What is the formula for osmotic pressure?
Π = iMRT where:
- i = van’t Hoff factor
- M = molarity
- R = gas constant
- T = temperature in Kelvin
Why is the measured van’t Hoff factor often less than the expected value?
Due to ion pairing in solution, which reduces the actual number of particles present compared to the theoretical maximum
How is measured van’t Hoff factor calculated?
i = ΔTf(measured)/ΔTf(calculated as nonelectrolyte)
What are Kb and Kf?
Kb is the molal boiling point elevation constant and Kf is the molal freezing point depression constant, specific to each solvent
