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# Lecture 16.4- Colligative Calcs (HONORS)

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Section 16.4 Lecture for Honors Chem

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### Lecture 16.4- Colligative Calcs (HONORS)

1. 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. 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. 3. 16.4 The unit molality and mole fractions are two additional ways in which chemists express the concentration of a solution.
4. 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. 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. 6. 16.6
7. 7. 16.6
8. 8. 16.6
9. 9. 16.6
10. 10. for Sample Problem 16.6
11. 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. 12. 16.7
13. 13. 16.4 Ethlylene Glycol (EG) is added to water as antifreeze.
14. 14. 16.7
15. 15. 16.7
16. 16. 16.7 Sample Problem 16.7
17. 17. for Practice Problem 16.7
18. 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. 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. 20. 16.4
21. 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. 22. 16.4
23. 23. 16.4
24. 24. 16.8
25. 25. 16.8
26. 26. 16.8
27. 27. 16.8
28. 28. for Sample Problem 16.8
29. 29. 16.9
30. 30. 16.9
31. 31. 16.9
32. 32. 16.9
33. 33. for Sample Problem 16.9
34. 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. 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. 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. 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