FACTORS AFFECTING SOLUBILITY

1. FACTORS AFFECTING SOLUBILITY

2. Structure effects- Vitamins • Fat-soluble (nonpolar) • Water-soluble (polar) • hydrophilic ( ’s H2O) • hydrophobic (’s H2O)

3. Pressure Effects • As pressure increases, gas solubility… • INCREASES!

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

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

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

7. Try this... • The solubility of O2 is 2.2 x 10-4 M at 0oC and .10 atm. Calculate the solubility of O2 at 0oC and 0.35 atm.

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

9. Temperature Effects • Most substances are more soluble at higher temps, but NOT ALL! • Na2SO4, Ce2(SO4)3

11. Temperature Effects • For gases… • solubility goes DOWN as temperature increases

13. Raoult’s Law • Raoult’s Law animation

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

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

17. The Reason • The vapor pressure of the water is greater than the vapor pressure of the salt water.

19. The Reason • The water tries to achieve equilibrium by evaporating. • The salt water tries to absorb the water.

20. Key Idea • The presence of a nonvolatile solute lowers the vapor pressure of a solvent.

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

23. Raoult’s Law • Psol’n = solventPosolvent • Psol’n=obs vp of sol’n • solvent= mol fract of solv • Posolvent=vp of pure solv

24. Raoult’s Law • C3H8O3 is a nonvolatile liq. What is the vp of a sol’n made by adding 164g of glyceryn to 338 mL of H2O at 39.8oC? The vp of pure H2O at 39.8oC is 54.74 torr and its density is 0.992 g/mL.

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

26. Such as... • What is the vp of a sol’n made by adding 52.9 g of CuCl2 to 800.0 mL of water at 52oC? The vp of water at 52.00C is 102.1 torr and its density is 0.987 g/mL.

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

28. LOOK! • At 29.6oC, H2O 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 H2O. The vp of sol’n is 28.6 torr. What is MM of Y?

29. But what if solute is volatile? • It will contribute to the vapor pressure of the system! • PTOT=APAo + BPBo

30. PTOT=APAo + BPBo • PTOT = Total vp • A, B=mol fraction A,B • Pao,Pbo=partial pressures of A and B

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

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

34. Negative deviation • Often when Hsol’n is large and neg • EX: acetone and water

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

36. Positive deviation • EX: polar ethanol and nonpolar hexane

38. Ideal Solution • Very similar molecules • benzene and toluene

39. For you to do... • The vp of pure hexane (C6H14) at 60.0oC is 573 torr. That of pure benzene (C6H6) at 60.0oC 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)

40. Homework • P 544 • 47, 51, 55, 58