1. Boiling and Freezing Point Problems

2. Objective:
Today I will be able to:
Calculate the boiling point elevation and freezing point depression for a given compound
Evaluation/Assessment:
Informal Assessment – monitoring student progress as they complete the practice problems
Formal Assessment – analyzing student responses to the problems and exit ticket
Common Core Connection
Make sense of problem and persevere in solving them
Look for and make use of structure

3. Lesson Sequence Evaluate: Warm – Up Evaluate: Review HW
Elaborate: BP and FP Problem Practice
Evaluate: Exit Ticket

4. Warm - Up Which compound is least soluble at 50oC?
What mass of KNO3 can
dissolve in 50 g of H2O
at 40oC ?

5. Objective Today I will be able to:
Calculate the boiling point elevation and freezing point depression for a given compound

6. Homework
Read the Article “How Does Salt Battle Road Ice” and write a summary covering how salt lowers the freezing point of ice.
Study for the Solutions Quiz on Tuesday, April 29

7. Agenda
Warm-Up
Review HW
BP and FP practice problems
Exit Ticket

8. Before we calculate… we need to talk about the Van’t Hoff Factor

9. Van’t Hoff Factor
Determines the moles of ions that are present when a compound dissolves in a solution
Covalent compounds do not dissociate
C12H22O11
1 mole (same for all nonelectrolytes)
Ionic Compounds can dissociate
NaCl  Na+ + Cl-
2 moles of ions (Van’t Hoff Factor = 2)
CaCl2  Ca Cl-
3 moles of ions (Van’t Hoff Factor = 3)

10. Determine the Van’t Hoff Factor for the following Compounds
C6H12O6
KCl
Al2O3
P2O5 1 2 5

11. Calculating Boiling and Freezing Points
Tb = Kb  m i
Kb : the molal boiling point elevation constant, which is a property of the solvent
Tb : added to the normal boiling point
i : the Van’t Hoff Factor

12. Calculating Boiling and Freezing Points
Tf = Kf  m  i
Kf : the molal freezing point depression constant, which is a property of the solvent
Tf : subtracted from the normal freezing point
i : the Van’t Hoff Factor

13. Boiling and Freezing Points and Electrolytes
Q: What is the expected change in the freezing point of water in a solution of grams of barium nitrate, Ba(NO3)2, in kg of water?

14. BP/FP Practice
How many grams of a molecular substance (molecular mass 50.0g/mol) must be added to 500.0g water to have a boiling point of °C?
Answer = 76.3 grams

15. Boiling and Freezing Point Practice Problems
Complete the practice problems at your desk. We will review the problems together.

16. Exit Ticket What is the Van’t Hoff Factor for the following compounds?
AlCl3
Mg3(PO4)2
C6H12O6 4 5 1