COLLIGATIVE PROPERTIES
the 4 physical effects solutes
can have on solutions
• COLLIGATIVE
PROPERTIES- the
physical properties
of solutions that are
affected by the
number of particles
and not the
identification of
dissolved solutes
1. BOILING POINT ELEVATION
– Liquids boil when the vapor
pressure equals the atmospheric
pressure
– By adding a solute, the
temperature at which the liquid
boils is higher.
– EX: adding salt to water when
cooking makes the water boil at
a higher temperature. Cooking
noodles will cook faster because
the water can reach a higher
temperature and your noodles
won’t be as soggy!
2. FREEZING POINT DEPRESSION
By adding a solute to water, the freezing
point is lowered..
EX: salt added to roads makes the water freeze
into ice at a lower temperature.
EX: antifreeze is added to a car radiator, so the
water will not freeze until it reaches a temperature
lower than 0
3. VAPOR PRESSURE LOWERING
Water pressure exerted in a closed
container by liquid particles that have
escaped the surface and entered the
gaseous state.
 by increasing the number of solute
particles, the vapor pressure is lowered
4. OSMOTIC PRESSURE
• Diffusion- the mixing
of gases or liquids due
to random motions
• Osmosis – different
solvent particles cross
a semi-permeable
membrane from an
area of high solvent
concentration to one
of lower
concentration.
Movement of water,
not the solute!!
1.2 M
0.45 M
A
A
B
B
A selectively permeable membrane
separates two aqueous solutions of
potassium chloride (KCl). On the left side
of the membrane is solution A composed
of 1.24 M solution. On the right side of the
membrane is solution B composed of 0.45
M solution.
Which side is most concentrated?
Which side has the most water?
Which way will the water flow?
ELECTROLYTES
• Ionic compounds are electrolytes
• This means that they dissociate in water
to form a solution that conducts electric
current
The 4 colligative properties, once
again are…
•
•
•
•
Increase in bp (bp elevation)
Decrease in fp (fp depression)
Lowering of vapor pressure
Osmotic pressure
TRY THESE…
MOLARITY
• What is the molarity of
a solution with 50 g
sodium carbonate
dissolved in 2000 mL of
water?
• M= mol/L
• 50 g Na2CO3 X 1 mol = .47mol
106 g
M= .47 mol
2L
= .2M
DILUTION
How many milliliters of 2.55M
NaOH is needed to make a 125
mL of a 0.75M NaOH?
M1V1=M2V2
(2.55M)(V1) = (0.75M)(125mL)
V1 = 36.8 mL