1. Chemistry 16.4

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

3. Molality and Mole Fraction
16.4
Molality and Mole Fraction
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.

4. Molality and Mole Fraction
16.4
Molality and Mole Fraction
To make a 0.500m solution of NaCl, use a balance to measure kg of water and add mol (29.3 g) of NaCl.
To make a 0.500m solution of NaCl, use a balance to measure kg of water and add mol (29.3 g) NaCl. Calculating What would be the molality if only kg of water were used?

5. Molality and Mole Fraction
16.4
Molality and Mole Fraction
Ethlylene Glycol (EG) is added to water as antifreeze.
Ethylene glycol (EG) is added to water as antifreeze in the proportions shown. A mole fraction is the ratio of the number of moles of one substance to the total number of moles of all substances in the solution. Inferring What is the sum of all mole fractions in a solution?

6. 16.6

7. 16.6

8. 16.6

9. 16.6

10. Practice ProblemsFor Sample Problem 16.6
Problem Solving Solve Problem 29 with the help of an interactive guided tutorial.

11. Molality and Mole Fraction
16.4
Molality and Mole Fraction
The mole fraction of a solute in a solution is the ratio of the moles of that solute to the total number of moles of solvent and solute.

12. Molality and Mole Fraction
16.4
Molality and Mole Fraction
In a solution containing nA mol of solute A and nB mol of solvent B (XB), the mole fraction of solute A (XA) and the mole fraction of solvent B (XB) can be expressed as follows.

13. 16.7
The concentration of antifreeze used in an automobile cooling system can be described by mole fractions.

14. 16.7

15. 16.7

16. 16.7
Sample Problem 16.7

17. for Practice Problem 16.7
Problem Solving Solve Problem 32 with the help of an interactive guided tutorial.

18. Freezing-Point Depression and Boiling-Point Elevation
16.4
Freezing-Point Depression and Boiling-Point Elevation
Freezing-Point Depression and Boiling- Point Elevation
How are freezing-point depression and boiling-point elevation related to molality?

19. Freezing-Point Depression and Boiling-Point Elevation
16.4
Freezing-Point Depression and Boiling-Point Elevation
The magnitudes of the freezing-point depression and the boiling-point elevation of a solution are directly proportional to the molal concentration (m), when the solute is molecular, not ionic.

20. Freezing-Point Depression and Boiling-Point Elevation
16.4
Freezing-Point Depression and Boiling-Point Elevation
The constant, Kf, is the molal freezing-point depression constant, which is equal to the change in freezing point for a 1-molal solution of a nonvolatile molecular solute.

21. Freezing-Point Depression and Boiling-Point Elevation
16.4
Freezing-Point Depression and Boiling-Point Elevation

22. Freezing-Point Depression and Boiling-Point Elevation
16.4
Freezing-Point Depression and Boiling-Point Elevation
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 a nonvolatile molecular solute.

23. Freezing-Point Depression and Boiling-Point Elevation
16.4
Freezing-Point Depression and Boiling-Point Elevation

24. Freezing-Point Depression and Boiling-Point Elevation
Simulation 21 Discover the principle underlying the colligative properties of solutions.

25. Freezing-Point Depression and Boiling-Point Elevation
16.4
Freezing-Point Depression and Boiling-Point Elevation
The graph shows the relationship between vapor pressure and temperature for pure water and aqueous solutions. INTERPRETING GRAPHS a. Identify What is the freezing point of water? What is the boiling point? b. Describe How do the freezing and boiling points of the solution compare to those of pure water? c. Apply Concepts Does adding a solute to water allow it to remain as a liquid over a longer or shorter temperature range? Explain.

26. 16.8

27. 16.8

28. 16.8

29. 16.8

30. for Sample Problem 16.8
Problem Solving Solve Problem 33 with the help of an interactive guided tutorial.

31. 16.9

32. 16.9

33. 16.9

34. 16.9

35. for Sample Problem 16.9
Problem Solving Solve Problem 36 with the help of an interactive guided tutorial.

36. 16.4 Section Quiz.
16.4.

37. 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?
0.60
1.5
0.20
0.11

38. 16.4 Section Quiz.
2. The freezing point depression caused by a given concentration of a nonvolatile molecular solute
depends on the solute.
depends on the solvent.
is always the same.
cannot be determined.

39. 16.4 Section Quiz.
3. What are the freezing and boiling points of a 0.1m solution of CaCl2 in water?
-0.2°C, 100.1°C
-0.6°C, 100.1°C
-0.6°C, 100.2°C
-0.6°C, 99.8°C

40. 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
exactly the same.
twice as large.
three times as large.
four times as large

41. END OF SHOW