1. Midterm I Review Thursday, Feb. 08: Huggins 10, 7-8 pm Conflicts: ELL 221, 6-7 pm No class on Friday, Feb. 09!

2. 13.26 The solubility of KNO 3 is 155 g per 100 g of water at 75 o C and 38.0 g at 25 o C. What mass (in grams) of KNO 3 will crystallize out of solution if exactly 100 g of its saturated solution at 75 o C are cooled to 25 o C?

3. Colligative properties Vapor-pressure lowering –Nonvolatile solute, ΔP = X 2 P 1 o –Does not apply to volatile solutes, P T = P A + P B (where P A = X A P A o ) Boiling-point elevation –ΔT b = K b m –Does not apply to volatile solutes Freezing-point depression –ΔT f = K F m –Applies to both volatile and nonvolatile solutes Osmotic pressure –Directly proportional to concentration of solution –As [solute] increases, so does osmotic pressure (pressure required to stop osmosis, which is the net movement of solvent molecules from a pure solvent or dilute solution to a more concentrated solution) Depend on amount of solute in solution, not on identity

4. Colligative properties You just dissolved a solute such as sugar in water. What happens to each of the following? –Melting point (freezing point) decreases –Boiling point increases –Vapor pressure decreases –Osmotic pressure increases Depend on amount of solute in solution, not on identity

5. Using colligative properties to determine molar mass Example 13.8 A 7.85-g sample of a compound is dissolved in 301 g of benzene. The freezing point of the solution is 1.05 o C below that of pure benzene. What is the molar mass of this compound?

6. Solutions and solubility In most, but not all cases, solubility of a solid substance increases with temperature The solubility of gases usually decreases with temperature The solubility of gases usually increases with pressure –Henry’s law, c = kP

7. Effect of pressure on the solubility of gases The solubility of N 2 in blood at 37 o C and at a partial pressure of 0.80 atm is 5.6 x 10 -4 mol L -1. What is the value of Henry’s Law constant? In M mmHg -1 ? Henry’s law, c = kP

8. Concentration units % by mass of solute –Mass of solute/mass of solution, where mass of solution is (mass of solute + mass of solvent) Molarity, M – Moles of solute/ volume of solution (L) Molality, m –Moles of solute/ mass of solvent (kg)

9. Concentration units % by mass of solute –Mass of solute/mass of solution, where mass of solution is (mass of solute + mass of solvent) Molarity, M – Moles of solute/ volume of solution (L) Molality, m –Moles of solute/ mass of solvent (kg) Calculate the molality and molarity of a 30% by mass solution of NH 3 in water. The density of the solution is 0.982 g/mL.

10. The rate constant The rate constant k for a given reaction depends on what parameters? The rate constant does NOT depend on the concentrations of reactants!

11. Rates of reaction For a first-order reaction, how long will it take for the concentration of reactant to fall to 1/8 its original value? Half-life of a 1 st order reaction does not depend on the concentration. Half-life t 1/2 is the time it takes for the concentration of reactant to decrease to ½ its initial value

12. Rates of reaction A plot of ln [A] vs. time gives a straight line –1 st order A plot of 1/[A] vs. time gives a straight line –2 nd order Determining reaction order graphically

13. Catalysts Rate constant –Increases Equilibrium constant –No change