1. CVEN 4424 Environmental Organic Chemistry
Lecture 7
Sorption of Neutral Organic Compounds to Dissolved Organic Matter
and
Air-Water Exchange Equilibrium

2. Announcements Reading Problem sets Office hours Exam 1
Chapter 5, Aqueous solubility
Chapter 9, Sorption (more of this later)
Problem sets
PS 3 due Thursday
PS 4 out Thursday
Office hours
Monday, am, ECES 115, Joe
Tuesday, 5-6:30 pm, ECES 115, Alejandro
Wednesday, am, ECES 115, Joe
Wednesday, 4:30-6 pm, ECES 115, Alejandro
Exam 1
Tuesday, February 17, in class
closed book; equations and data available on exam

3. Aqueous Solubility Organic liquid mixtures
petroleum – gasoline, oil, kerosene
coal tar
PCBs – Arochlor

4. Aqueous Solubility Solubility of an organic liquid assumptions
xL  1 (essentially no water in organic phase)
L = 1 (pure liquid; ideal interactions) w L

5. Aqueous Solubility Solubility of an organic liquid mixture assumptions
xL is the mole fraction of the compound of interest
L  1 (not a pure liquid, but nearly ideal interactions) w L

6. Coal tar
BTEX
PAHs

7. Aqueous Solubility Organic liquid mixtures org mix  1 to 5 xorg mix
need average mw of organic liquid mixture
e.g., coal tar 150 g mol-1
no melting costs
compound is already in liquid phase in organic mixture

8. Aqueous Solubility
Organic liquid mixtures example: What concentration of benzene should we find in water in equilibrium with gasoline containing benzene at a concentration of 1 vol%?

9. Aqueous Solubility
Benzene in water in equilibrium with gasoline containing 1 vol% benzene?
Need estimates for and

10. Aqueous Solubility
Benzene in water in equilibrium with gasoline containing 1 vol% benzene?
activity coefficient of benzene in gasoline,
mole fraction of benzene in gasoline,

11. Aqueous Solubility
Benzene in water in equilibrium with gasoline containing 1 vol% benzene?
activity coefficient of benzene in water,

12. Aqueous Solubility
Benzene in water in equilibrium with gasoline containing 1 vol% benzene? benzene MCL: g L-1

13. Solubility and Organic Matter

14. DOM Suwannee River humic acid Suwannee River fraction 10 mgC L-1
fulvic acid
fraction
10 mgC L-1
Everglades
hydrophobic acid
fraction
10 mgC L-1
Williams Lake
hydrophobic acid
fraction
10 mgC L-1

17. Solubility and Organic Matter
Dissolved organic matter (DOM)
terrestrial source
plants; “allochthonous”
more soluble, higher molecular weight, more aromatic
aquatic source
organisms; “autochthonous”
less soluble, lower molecular weight, less aromatic
Kerner et al., 2003, Nature 422,

18. Solubility and Organic Matter
Dissolved organic matter
“dissolved” is operational
membrane filtration
0.45 m
glass fiber filtration m
ultrafiltration
molecular weight cutoffs
1,000-10,000 Da
tangential flow filtration

19. Solubility and Organic Matter

20. Solubility and Organic Matter

21. Solubility and Organic Matter
Ultraviolet light absorption

22. Solubility and Organic Matter
Fractionation
glass fiber-filtered
sample at pH 2
fulvic
acid
hydrophobic
organic acid
“transphilic”
organic acid
NaOH
NaOH
pH 2
XAD-8 resin
humic
acid
XAD-4 resin
hydrophobic
organic neutral
“transphilic”
organic neutral
CH3CN
CH3CN
hydrophilic organic acid

23. Solubility and Organic Matter
Adoc Aw + =

24. Solubility and Organic Matter
Binding to DOM
binding, not absorption
one molecule of solute bound by a single DOM molecule
like co-solvency
readily reversible
solute release from DOM not diffusion-limited like release from SOM

25. Solubility and Organic Matter
Measurement of Kdoc: techniques
headspace analysis
volatile compounds only
solid phase microextraction
only for low solubility compounds
solubility enhancement
microcrystals/emulsions?
fluorescence quenching
fluorescent compounds only
“dynamic quenching” questions

26. Solubility and Organic Matter
Solubility enhancement

27. Solubility and Organic Matter
If you use headspace analysis for measurement of Kdoc for a volatile organic compound (VOC), which trend would you expect? A. the amount of VOC in the headspace increases as DOC increases B. the amount of VOC in the headspace decreases as DOC increases ? ? ?

29. Air-Water Exchange Equilibrium

30. p* Cwsat Air-Water Exchange Phase transfers vaporization/sublimation
aqueous solution
vapor p*
Cwsat
pure
liquid
pure
liquid
aqueous
solution

31. = Air-Water Exchange Another phase exchange air-water exchange vapor
pure
liquid
aqueous
solution
aqueous
solution

32. Air-Water Exchange Phase exchange Awater  Aair Henry’s Law constants
(bar L mol-1)
dimensionless
(mol La-1 mol-1 Lw)

33. Air-Water Exchange compound Henry’s Law constant Kaw (dimensionless)
benzene
phenol
trichloroethene
phenanthrene
2,2’,5,5’-tetrachlorobiphenyl

34. Air-Water Exchange
Estimates by vapor pressure / solubility

35. Air-Water Exchange Example: chloroethene (a gas)
estimated Kaw =
experimental Kaw =

36. Air-Water Exchange Example: chlorobenzene (a liquid)
estimated Kaw =
experimental Kaw =

37. Air-Water Exchange Example: pyrene (a solid) estimated Kaw = 10-3.32
experimental Kaw =

38. Air-Water Exchange Temperature dependence
enthalpy of liquid-air phase change, alH
Two components of alH: vapH - wHE
enthalpy to vaporize vapH, related to pL*
(excess) enthalpy to solubilize wHE, related to Cwsat
for solids and gases, melting and condensation enthalpies cancel out

39. gas already in gas phase
Air-Water Exchange
Liquid:
Solid:
Gas:
(getting to
gas phase)
(getting out of
water phase)
gas already in gas phase

40. Air-Water Exchange dichlorodifluoromethane (gas) toluene (liquid)
naphthalene (solid)
pyrene (solid)

41. + = Air-Water Exchange Temperature dependence
liquids (e.g., benzene, tetrachloroethylene)
ln p*
1/T
ln Cwsat
1/T
ln KH
1/T + =

42. + = Air-Water Exchange Temperature dependence
solids (e.g., naphthalene, 1,4-dichlorobenzene)
ln p*
1/T
ln Cwsat
1/T
ln KH
1/T + =

43. + = Air-Water Exchange Temperature dependence
gases (e.g., vinyl chloride, chloromethane)
ln p*
1/T
ln Cwsat
1/T
ln KH
1/T + =

44. Air-Water Exchange Effect of salt
Salting out decreases solubility; increases Kaw

45. Air-Water Exchange Effect of salt pyrene, Kaw = 10-3.32 seawater
[salt]tot = 0.5 M
KS = 0.30

46. Air-Water Exchange Effect of co-solvents
Co-solvents increase solubility; decrease KH

47. Air-Water Exchange Effect of co-solvents naphthalene, Kaw = 10-1.74
20% acetone solution
fv = 0.2
c = 6.5

48. Air-Water Exchange Partition between air and water
importance of keeping bubbles out of water samples for VOCs
40 mL vial
39 mL water, 1 mL bubble
VOC is chloromethane
Kaw =
what fraction of the chloromethane is in the bubble?

49. Air-Water Exchange
Partition between air and water

50. Next Lecture
Air-Water Exchange Kinetics
Read Chapters 18, 19, and 20