2. FACTORS AFFECTING SOLUBILITY

3. Structure effects- Vitamins w Fat-soluble (nonpolar) w Water-soluble (polar) w hydrophilic (  ’s H 2 O) w hydrophobic (  ’s H 2 O)

4. Pressure Effects w As pressure increases, gas solubility… w INCREASES!

5. Henry’s Law w P=kC w P= partial pressure of gaseous solute above sol’n w C= conc of dissolved gas w k = const for specific sol’n

6. Henry’s Law w The amount of a gas dissolved in a solution is directly proportional to the pressure of the gas above the solution

7. Henry’s Law w Works best when: w dilute sol’ns of gases w do not dissociate with solvent w do not react with solvent

8. Try this... w The solubility of O 2 is 2.2 x 10 -4 M at 0 o C and.10 atm. Calculate the solubility of O 2 at 0 o C and 0.35 atm.

9. Temperature Effects w As the temperature of a liquid increases, the ability for a solute to dissolve… w increases? SOMETIMES!

10. Temperature Effects w Most substances are more soluble at higher temps, but NOT ALL! w Na 2 SO 4, Ce 2 (SO 4 ) 3

12. Temperature Effects w For gases… w solubility goes DOWN as temperature increases

14. Raoult’s Law w Raoult’s Law animation Raoult’s Law animation

15. An Experiment w Two beakers are placed in a sealed chamber. One has water and the other has salt water.

16. An Experiment w Eventually, the water beaker is empty and the salt water beaker has twice the water… w WHY?

18. The Reason w The vapor pressure of the water is greater than the vapor pressure of the salt water.

20. The Reason w The water tries to achieve equilibrium by evaporating. w The salt water tries to absorb the water.

21. Key Idea w The presence of a nonvolatile solute lowers the vapor pressure of a solvent.

22. Think about it… w The solute lowers the number of gas molecules that can reach the surface and turn to vapor.

24. Raoult’s Law w P sol’n =  solvent P o solvent w P sol’n =obs vp of sol’n w  solvent = mol fract of solv w P o solvent =vp of pure solv

25. Raoult’s Law w C 3 H 8 O 3 is a nonvolatile liq. What is the vp of a sol’n made by adding 164g of glyceryn to 338 mL of H 2 O at 39.8 o C? The vp of pure H 2 O at 39.8 o C is 54.74 torr and its density is 0.992 g/mL.

26. Multiple Ions? w When a substance breaks up into more than one ion, it essentially has twice the effect that it is supposed to have.

27. Such as... w What is the vp of a sol’n made by adding 52.9 g of CuCl 2 to 800.0 mL of water at 52 o C? The vp of water at 52.0 0 C is 102.1 torr and its density is 0.987 g/mL.

28. Molar Mass? w Mass of cmpd is dissolved in a solvent and the vp of resulting sol’n is measured. This will give us # of moles. w g/mol is molar mass!

29. LOOK! w At 29.6 o C, H 2 O has a vp of 31.1 torr. A sol’n is prepared by adding 86.7 g of “Y” (nonvolatile, nonelectro) to 350.0 g H 2 O. The vp of sol’n is 28.6 torr. What is MM of Y?

30. But what if solute is volatile? w It will contribute to the vapor pressure of the system! w P TOT =  A P A o +  B P B o

31. P TOT =  A P A o +  B P B o w P TOT = Total vp w  A,  B =mol fraction A,B w P a o,P b o =partial pressures of A and B

33. Ideal Solution w When a liquid-liquid solution obey Raoult’s law w When sol-sol, solv-solv and sol-solv interactions are similiar

34. Negative deviation w If the solute has an affinity for the solvent (H-bond) w Obs vapor pressure will be less than expected

35. Negative deviation w Often when  H sol’n is large and neg w EX: acetone and water

36. Positive deviation w Solute-solvent interactions are weaker than the interactions in the pure liquids w higher vp then expected

37. Positive deviation w EX: polar ethanol and nonpolar hexane

39. Ideal Solution w Very similar molecules w benzene and toluene

40. For you to do... w The vp of pure hexane (C 6 H 14 ) at 60.0 o C is 573 torr. That of pure benzene (C 6 H 6 ) at 60.0 o C is 391 torr. What is the expected vp of a sol’n prepared by mixing 58.9g hexane and 44.0g benzene. (ideal sol’n)

41. Homework w P 544 w 47, 51, 55, 58