1. (B) Adding a nonvolatile solute to a solvent decreases
the solution’s freezing point (FP) and increases its
boiling point (BP).
pure solvent
Phase diagram T P
solid
liquid
gas
1 atm
(not water’s)
solution
Note that FP
and BP .
NFP
NBP

2. The freezing point depression and
boiling point elevation are given by:
DTx = Kx m i
DTx = FP depression or BP elevation
Kx = Kf (molal FP depression constant) or
Kb (molal BP elevation constant)
-- they depend on the solvent
-- for water: Kf = 1.86oC/m
Kb = 0.52oC/m
m = molality of solute

3. Jacobus Henricus van’t Hoff
i = van’t Hoff factor
(accounts for # of
particles in solution)
In aq. soln., assume that…
-- i = __ for nonelectrolytes 1
-- i = __ for KBr, NaCl, etc. 2
Jacobus Henricus van’t Hoff
(1852 – 1911)
-- i = __ for CaCl2, etc. 3
In reality, the van’t Hoff factor isn’t always
an integer. Use the guidelines unless
given information to the contrary.

4. Find the FP and BP of a soln. containing 360. g barium
chloride and 2.50 kg of water.
Kf = 1.86oC/m
Kb = 0.52oC/m
DTx = Kx m i
360 g BaCl2
= mol BaCl2
0.690 m
i = 3
DTf = Kf m i
= 1.86(0.690)(3)
= 3.85oC
FP = –3.85oC
DTb = Kb m i
= 0.52(0.690)(3)
= 1.08oC
BP = oC

5. Camphor, C10H16O, has an NFP of 179.8oC and a
Kf of 40.0oC/m. When g of a nonelectrolytic
substance is dissolved in g of camphor, the
mixture’s new freezing point is 176.7oC. Find the
unknown’s molar mass.
3.1oC
DTf = Kf m i
40.0
1 (organic = nonelec.)
(Multiply by kg
camphor to get…)
Solve for m =
mol unknown
kg camphor
1.71 x 10–3 mol unk. =
1 mol unk.
X g unk.
X = 109 g/mol
0.186 g unk.