1. Outline1/12/07 è First Chem seminar today… è Pick up CAPA #2 - in front è ChemBoard Assignment = Monday è Fill in keypad response unit #’s… Today: Surfactants Colligative Properties Calculating Colligative Effects

2. Surfactants: n n Anything which alters behavior of solute-solvent mixture….(e.g. soap) Applications? NaCl in cooking Road salt for ice Antifreeze Saline drips Gatorade e.g. Demo of S on water

3. Effect of solutes on solvent properties... Vapor pressures Boiling points Freezing points Osmotic pressure “Colligative properties”

4. Calculations of Colligative Property effects n n Freezing Point Depression    T = K f m n n Boiling Point Elevation    T = K b m where K f and K b are constants and m is concentration of solute in terms of molality (mols/kg solvent) K f =  1.858°C/m K b = 0.512°C/m

5. liquid solid

6. Calculations of Colligative Property effects n n Freezing Point Depression    T = K f m n n Boiling Point Elevation    T = K b m where K f and K b are constants and m is concentration of solute in terms of molality (mols/kg solvent) K f =  1.858°C/m K b = 0.512°C/m

7. Example #1: n n Estimate the freezing point of wine that is 12% by mass ethanol... Freezing Point Depression:  T = K f m K f =  1.858  C kg/mol (for water) 12g C 2 H 5 OH  46 g/mol = 0.261 mol Assume 100g of wine, then you have 12g ethanol and 88g H 2 O... 0.261 mol EtOH/88 g H 2 O = x mol/1000g x = 2.97 m  T =  5.5°C

8. Example #2: Compute the molar mass of A, if a solution containing 35.0 g of A dissolved in 135 mL of H 2 O freezes at  1.75  C. Assume A does not ionize in water. Freezing Point Depression:  T = K f m K f =  1.858  C kg/mol (for water)  =  1.858 m or m = 0.942 mol/kg

9. Example #2 (cont’d): n n m = 0.942 mols solute/kg solvent n n How many kg of solvent? Molar mass:  g / 0.127 mol = 275 g/mol 135 mL  1 g/mL = 135 g = 0.135 kg 0.942 mol/kg  0.135 kg = 0.127 mol

10. Another useful application:   Osmotic Pressure (  ) Passage of solute molecules through a semi-permeable membrane Start with something we know: PV = nRT (ideal gases) or P = (n/V)RT Adapt to solutions: (n/V)  (mol/L) = Molarity!

11.   Osmotic Pressure (  )  = M RT p.107

13. Example: Compute the molar mass of hemoglobin, if a 25 mL solution containing 0.420 g of hemoglobin has an osmotic pressure of 4.6 torr at 27  C. Osmotic pressure:  = M RT M = [m (g) / MM (g/mol)]/V  m (RT)/ (MM) V = 68300 g/mol

14. Practice…Worksheet #1 n n Remember to keep solute & solvent separate when answering questions!

15. Henry’s Law n n Gases dissolved in a liquid: Concentration = K H p Examples: soda CO 2, NO x, SO x and acid rain

16. For Monday… n n Do CAPA set #1 n n Post a trial message on Chemboard n n Read through Chapter 12 …get ahead! Have a great week-end!