Section 16.3 lecture, on colligative properties of solutions, for honors and prep chemistry

1. Bellwork
Write out a numbered list of steps that
you could follow to prepare a 1M
aqueous solution of KCl.

2. Colligative Properties of Solutions
The wood frog is a
remarkable creature
because it can survive being
frozen. Scientists believe
that a substance in the cells
of this frog acts as a natural
antifreeze, which prevents
the cells from freezing. You
will discover how a solute
can change the freezing
point of a solution.

3. 16.3 Vapor-Pressure Lowering
Colligative properties depend on
the number of dissolved particles.
It doesn’t matter what type of
particle it is.

4. 16.3
Three important colligative
properties of solutions are
• vapor-pressure lowering
• boiling-point elevation
• freezing-point depression

5. 16.3
In a pure solvent, equilibrium is
established between the liquid and the
vapor.

6. 16.3
In a solution, solute particles reduce the
number of free solvent particles able to
escape the liquid.
Equilibrium is established at a lower vapor
pressure.

7. 16.3
The decrease in a solution’s
vapor pressure is proportional
to the number of particles the
solute makes in solution.

8. 1 mol glucose = 1 mol particles
1 mol NaCl = 2 mol particles
(1 mol Na+ and 1 mol Cl-)
1 mol CaCl2 = 3 mol particles
(1 mol Ca2+ and 2 mol Cl-)
1 mole of CaCl2 has the most effect
because it makes more particles

9. 16.3
The difference in temperature between
the freezing point of a solution and the
freezing point of the pure solvent is the
freezing-point depression.

10. 16.3
The magnitude of the
freezing-point
depression is proportional to the
number of solute particles
dissolved in the solvent and does
not depend upon their identity.

11. 16.3
Adding salt to icy
roads and sidewalks
lowers the freezing
point of water.
Much or all of the
ice will melt.

12. 16.3
Boiling-Point Elevation
The difference in temperature between the
boiling point of a solution and the boiling
point of the pure solvent is the boiling-point
elevation.
The same antifreeze added to automobile
engines to prevent freeze-ups in winter,
protects the engine from boiling over in
summer.

13. 16.3
The magnitude of the
boiling-point
elevation is proportional to the
number of solute particles
dissolved in the solvent.
The boiling point of water increases by
0.512°C for every mole of particles that
the solute forms when dissolved in
1000 g of water.

14. Colligative Properties depend on the
amount of dissolved particles
NOT THE TYPE.
These are the
same thing. Lower
Vapor pressure is lowered
vapor pressure =
higher boiling
point!!
Boiling point is elevated
The temperature
range over which
water is a liquid is
Freezing point is depressed increased.