Section 16.4 Lecture for Honors Chem

1. Bellwork- Colligative Fill-in
Chemistry 16.4
Colligative properties depend only on the _________
of solute particles and not on the __________ of
solute particles.
A mole of ionic solute will produce a _______
change in colligative properties than a mole of
molecular (covalent) solute because it will produce
_________ particles.
Colligative properties include vapor pressure
________, freezing point ________, and boiling point
________.
Fill- in the blank exercises are __________.

2. Calculations Involving Colligative Properties
Cooking instructions
often call for the addition
of a small amount of salt
to the cooking water.
Dissolved salt elevates
the boiling point of
water. You will learn how
to calculate the amount
the boiling point of the
cooking water rises.

3. 16.4
The unit molality and mole fractions are
two additional ways in which chemists
express the concentration of a solution.

4. 16.4
The unit molality (m) is the number of
moles of solute dissolved in 1 kilogram
(1000 g) of solvent.
Molality is also known as molal
concentration.

5. 16.4
To make a 0.500m
solution of NaCl, use
a balance to
measure 1.000 kg of
water and add 0.500
mol (29.3 g) of NaCl.

6. 16.6

7. 16.6

8. 16.6

9. 16.6

10. for Sample Problem 16.6

11. 16.4
The mole fraction of a solute is
moles of solute divided by
total moles (moles solute + moles solvent).
nA = moles of A

12. 16.7

13. 16.4
Ethlylene Glycol (EG) is added to water
as antifreeze.

14. 16.7

15. 16.7

16. 16.7
Sample Problem 16.7

17. for Practice Problem 16.7

18. 16.4
The freezing-point depression (∆Tf) and the
boiling-point elevation (∆Tb) of a solution are
directly proportional to the molal
concentration (m) of solute particles.

19. 16.4
∆Tf = i Kf m
Kf is a constant, the molal freezing-
point depression constant, which is
different for every solvent.
i is the number of particles the solute
makes.
NaCl i = 2
MgCl2 i = 3

20. 16.4

21. 16.4
∆Tb = i Kb m
The constant, Kb, is the molal boiling-
point elevation constant, which is equal
to the change in boiling point for a 1-
molal solution of particles.
1m MgCl2 = 3m particles
1m sugar = 1m particles

22. 16.4

23. 16.4

24. 16.8

25. 16.8

26. 16.8

27. 16.8

28. for Sample Problem 16.8

29. 16.9

30. 16.9

31. 16.9

32. 16.9

33. for Sample Problem 16.9

34. 16.4 Section Quiz.
1. What is the mole fraction of He in a gaseous
solution containing 4.0 g of He, 6.5 g of Ar,
and 10.0 g of Ne?
a. 0.60
b. 1.5
c. 0.20
d. 0.11

35. 16.4 Section Quiz.
2. The freezing point depression caused by a
given concentration of a nonvolatile molecular
solute
a. depends on the solute.
b. depends on the solvent.
c. is always the same.
d. cannot be determined.

36. 16.4 Section Quiz.
3. What are the freezing and boiling points of a
0.1m solution of CaCl2 in water?
a. -0.2°C, 100.1°C
b. -0.6°C, 100.1°C
c. -0.6°C, 100.2°C
d. -0.6°C, 99.8°C

37. 16.4 Section Quiz.
4. Compared to the freezing point depression by
ethylene glycol (C2H6O2,) for a given solvent,
the freezing point depression caused by the
same molal concentration of CaCl2 would be
a. exactly the same.
b. twice as large.
c. three times as large.
d. four times as large