Lecture 3 & 4 (Ch. 13): Molality/Mole Fraction, Van Hoff Factor, VP Lowering Flashcards
parts per million (ppm) equation and units
ppm= mass of component/total mass of soln
-units: none
mole fraction
X(sub A)= moles of A/ total moles of all components
- units: none
- subscript(A) is component of interest
molality
m=moles of solute/kg of solvent
- units: mol/kg
- must know density of soln to convert btwn M & m
what is water’s density?
-1.00g/mL @ 25°C
OR
-1.00kg/L
when are M & m equal?
-if water is solvent for dilute solns
what does colligative properties depend on?
- quantity, not kind of particles
- concentration is important
types of colligative properties
- vapor pressure lowering
- boiling point elevation
- freezing point depression
- osmotic pressure
colligative property
-a property of a solution that depends on the number of particles of solute in a given volume of solvent
van’t hoff factor (i)
- compensates for # of solute particles dissolved
- can be estimated and calculated
what do non-electrolytes break up into and how to estimate their van’t hoff factor?
- dissolve as entire molecule
- estimated i: 1
- includes molecular compounds (i.e. glucose)
what do strong electrolytes break up into and how to estimate their van’t hoff factor?
- dissolve 100% into many ions
- estimated i: # of ions
- includes ionic, strong acids or strong base
why is the calculated van’t hoff factor (i) less than the estimated for ionic compounds?
- cations & anions can re-associate forming an ionic pair which acts as a single particle resulting in solute particle conc. being less than estimated #
- ion pairing occurs more as conc. of solute increases
vapor pressure (VP)
- pressure exerted by a gas on a liquid at equilibrium
- high VP= many gas molecules present
volatile
- exhibits vapor pressure
- i.e. acetone
nonvolatile
- doesn’t exhibit vapor pressure
- i.e. glycerin
