CVEN 4424Environmental Organic Chemistry

Lecture 7

Sorption of Neutral Organic Compounds to Dissolved Organic Matter andAir-Water Exchange Equilibrium

Announcements Reading

Chapter 5, Aqueous solubility Chapter 9, Sorption (more of this later)

Problem sets• PS 3 due Thursday• PS 4 out Thursday

Office hours Monday, 10-11 am, ECES 115, Joe Tuesday, 5-6:30 pm, ECES 115, Alejandro Wednesday, 10-11 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

Aqueous Solubility Organic liquid mixtures

petroleum – gasoline, oil, kerosene coal tar PCBs – Arochlor

Aqueous Solubility Solubility of an organic liquid

assumptions xL 1 (essentially no water in organic phase)

L = 1 (pure liquid; ideal interactions)

Lw

ln ln

ln ln ( )(1

ln

1)w ww

w

L

w

L

w

w

w w

x

x

G

x

RT RT

G

x

RT RT

G RT

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) Lw

ln ln

ln ln (1)

ln

L L

L

w w

w w

w w

w

L

w

w

x

x

G RT RT

G RT RT

G R

x

x

Txx

Coal tar BTEX PAHs

Aqueous Solubility Organic liquid

mixtures org mix 1 to 5

xorg mix need average mw of

organic liquid mixture

e.g., coal tar150 g mol-1

no melting costs compound is already

in liquid phase in organic mixture

orgmix

orgmix orgmix

orgmix orgmi

w

w w

ww

w

x

orgmix orgmix

ww

x x

Cx

x

V

x

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%?

Aqueous Solubility Benzene in water in equilibrium with

gasoline containing 1 vol% benzene?

Need estimates for and

bz

orgmix orgmixw

ww

bz bzgas gasbzww w

xC

V

x

V

, ,bz bz bzgas gas wx

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,bzgasx

bzgas

assume 1bzgas

4 1

4 1 1

1mLbz 1vol%

100mL

1mL 0.877g 1mol1.12 10 mol mL

100mL 1mL 78.11g

1mL 110g1.12 10 mol mL 0.16mol mol

0.75g 1mol

bzgas

gas

bz bz bz bzgas bz gas

gas bz bz

gas gasbzgas bz gas bz gas

gas gas

x

x

Aqueous Solubility Benzene in water in equilibrium with

gasoline containing 1 vol% benzene? activity coefficient of benzene in water,bz

w

1.65 1

1

1 110 M 0.018Lmol

2,480

satw sat

w w

satw sat

ww

satw

CV

C V

Aqueous Solubility Benzene in water in equilibrium with

gasoline containing 1 vol% benzene?

benzene MCL: 5 g L-1

1

1

3

3

1 1

1 0.16mol molbz

2,480 0.018L mol

bz 3.6 10 M

78.11gbz 3.6 10 M

1mol

bz 0.28gL 28,000μgL

bz bzbz gasgas gas

bzww w w w

w

bzw

bz

w

x

V

Solubility and Organic Matter

DOM

Williams Lake hydrophobic acid

fraction10 mgC L-1

Suwannee Riverfulvic acidfraction

10 mgC L-1

Suwannee Riverhumic acid

fraction10 mgC L-1Everglades

hydrophobic acidfraction

10 mgC L-1

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 K

ern

er

et

al., 2

00

3, N

atu

re 4

22

, 1

50

-15

4.

Solubility and Organic Matter Dissolved organic

matter “dissolved” is

operational membrane filtration

0.45 m glass fiber filtration

0.7-0.8 m

ultrafiltration molecular weight cutoffs 1,000-10,000 Da

tangential flow filtration

Table X. Elemental Analysis Results

Elemental Analysis (%)Sample C H O N S Ash Source O:C H:C

Pacific Ocean FA 58 6.1 35 1.5 0.4 c 0.60 0.11Lake Fryxell FA 55 5.5 35 3.1 1.8 1.0 d 0.63 0.10Missouri River FA 55 5.3 35.0 1.3 0.8 0.1 a 0.63 0.102BS HPoA 52 4.8 40 1.6 1.2 7.3 b 0.77 0.09Ohio River FA 56 5.4 36 1.5 1.3 0.6 a 0.65 0.10Ogeechee River FA 54 4 39 0.9 1.3 0.4 a 0.71 0.07Suwannee River FA 54 3.9 38.0 0.7 0.4 0.2 a 0.70 0.07Coal Creek FA 53 4.5 38 1 0.7 1.2 a 0.73 0.09F1 HPoA 52 4.6 40 1.5 1.7 9.4 b 0.76 0.09Ogeechee River HA 53 5.6 40.0 2.0 c 0.76 0.11Ohio River HA

Sources:aAiken and Malcolm, 1987bRavichandran, 1999cAiken, Unpublished datadAiken, 1996

Solubility and Organic Matter

Table X3. Molecular Weight and 13C-NMR AnalysisResults for Humic Substances

Mn Liquid state 13C-NMR Analysis (% of total C) Aromatic:

Sample (Daltons) Aliphatic I Aliphatic II Acetal Aromatic Carboxyl Ketone Aliphatic I

Pacific Ocean FA 56.9 13.4 1.2 7.3 19.5 1.6 f 0.13

Lake Fryxell FA 562 d 47.6 12.4 3.2 13.0 20.2 3.6 g 0.27

Missouri River FA 839 e 40.0 11.9 4.5 20.4 18.8 4.4 e,f 0.51

2BS HPoA 953 b 39.5 9.2 1.6 21.3 22.2 6.3 f 0.54

Ohio River FA 705 d 33.6 11.6 5.6 24.3 18.6 6.4 d,f 0.72

Ogeechee River FA 39.4 7.5 3.1 26.6 20.2 3.3 f 0.68

Suwannee River FA 1360 b 29.3 12.0 7.0 24.8 21.1 5.9 d,f 0.85

Coal Creek FA 1180 d 34.7 8.1 1.6 28.0 23.1 4.5 f 0.81

F1 HPoA 1030 b 33.1 8.9 2.3 25.4 23.1 7.2 f 0.77

Ogeechee River HA 24.7 10.4 7.3 40.8 15.1 1.6 f 1.65

Ohio River HA

Sources:aAiken and Malcolm, 1987bRavichandran, 1999cAiken et al. 1992dChin et al., 1997eChin et al., 1994fAiken, Unpublished datagAiken, 1996

Solubility and Organic Matter

Solubility and Organic Matter Ultraviolet light absorption

13C-NMR aromatic content (percent)

0 10 20 30 40

SU

VA

254 (

L m

g-C

-1 c

m-1

)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

Solubility and Organic Matter Fractionation

glass fiber-filteredsample at pH 2

XAD-8 resin

XAD-4 resin

hydrophobicorganicacid

NaOH

hydrophobicorganicneutral

CH3CN

“transphilic”organicacid

NaOH

“transphilic”organicneutral

CH3CN

hydrophilicorganic acid

fulvicacid

humicacid

pH 2

Solubility and Organic Matter

+ =

[ ][ ]

docw doc doc

w

AA A K

A

Aw

Adoc

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

[ ][ ]

w doc

docdoc

w

A AA

KA

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

[humic substance] (mg-C L-1)

0 5 10 15 20 25 30

[BaP

] (

g L-

1 )

0

5

10

15 Coal Creek FA

Solubility and Organic Matter Solubility enhancement

[ ]sat sat satdoc w w doc

doc satw

C C C K doc

slopeK

C

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 theheadspace increasesas DOC increases

B. the amount of VOC in theheadspace decreasesas DOC increases

? ? ?

Air-Water Exchange Equilibrium

Air-Water Exchange Phase transfers

vaporization/sublimation aqueous solution

pureliquid

vapor

pureliquid

aqueoussolution

p* Cwsat

Air-Water Exchange Another phase exchange

air-water exchange

=pureliquid

aqueoussolution

vapor

aqueoussolution

vapor

Air-Water Exchange Phase exchange

Awater Aair

Henry’s Law constants

[ ][ ]

[ ]

AH

water

airaw

water

pK

AA

KA

(bar L mol-1)

dimensionless(mol La

-1 mol-1 Lw)

Air-Water Exchange

compoundHenry’s Law constantKaw (dimensionless)

benzene 10-0.65

phenol 10-4.59

trichloroethene 10-0.31

phenanthrene 10-2.85

2,2’,5,5’-tetrachlorobiphenyl 10-1.70

OH

Cl

H

Cl

Cl

Cl

Cl

Cl

Cl

Air-Water Exchange Estimates by vapor pressure /

solubility *( ), ,

*( ), ,

( , , )

1( , , )

g l sH sat

w

g l saw sat

w

pK

C g l s

pK

RTC g l s

Air-Water Exchange Example: chloroethene (a gas)

estimated Kaw = 10-0.04

experimental Kaw = 10-0.05

1.35 11.35

0.041.35 -1 1

1bar10 barLmol

( ) 10 M

1( )

1bar 110

10 (0.083barLmol K )(298.15K)

gH sat

w

gaw sat

w

pK

C g

pK

RTC g

M

H

H

Cl

H

Air-Water Exchange Example: chlorobenzene (a liquid)

estimated Kaw = 10-0.80

experimental Kaw = 10-0.82

1.80*0.59 1

2.39

*

1.800.80

2.39 -1 1

10 bar10 barLmol

( ) 10 M

1( )

10 bar 110

10 M (0.083barLmol K )(298.15K)

LH sat

w

Law sat

w

pK

C L

pK

RTC L

Cl

Air-Water Exchange Example: pyrene (a solid)

estimated Kaw = 10-3.32

experimental Kaw = 10-3.36

* 8.091.93 1

6.16

*

8.093.32

6.16 -1 1

10 bar10 barLmol

( ) 10 M

1( )

10 bar 110

10 M (0.083barLmol K )(298.15K)

SH sat

w

Saw sat

w

pK

C S

pK

RTC S

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 Cw

sat

for solids and gases, melting and condensation enthalpies cancel out

1ln al

H

HK c

R T

Air-Water Exchange Liquid:

Solid:

Gas:gas already

in gas phase

(getting togas phase)

(getting out ofwater phase)

(0)

0

Eal i vap i w

al i sub i w

Efus i vap fus i w

Evap i w

al i w

Evap i w

Evap i w

H H H

H H H

H H H H

H H

H H

H H

H H

Air-Water Exchange

log Kaw = -1400 T-1 + 5.83

log Kaw = -1190 T-1 + 3.44

log Kaw = -1490 T-1 + 3.50

log Kaw = -2260 T-1 + 4.42

-4.00

-3.00

-2.00

-1.00

0.00

1.00

2.00

0.0032 0.0033 0.0034 0.0035 0.0036 0.0037

1/T (K-1)

log

Ka

w

dichlorodifluoromethane (gas)

toluene (liquid)

naphthalene (solid)

pyrene (solid)

Air-Water Exchange Temperature dependence

liquids(e.g., benzene, tetrachloroethylene)

ln p

*

1/T

ln C

wsa

t

1/T

ln K

H

1/T

=+

*L

H satw

pK

C

Air-Water Exchange Temperature dependence

solids(e.g., naphthalene, 1,4-dichlorobenzene)

ln p

*

1/T

ln C

wsa

t

1/T

ln K

H

1/T

=+

*L

H satw

pK

C

Air-Water Exchange Temperature dependence

gases(e.g., vinyl chloride, chloromethane)

ln p

*

1/T

ln C

wsa

t

1/T

ln K

H

1/T

=+

*L

H satw

pK

C

Air-Water Exchange Effect of salt

Salting out decreases solubility; increases Kaw

,

,,

[ ],

,

,

10S

tot

asatw salt

asatw salt

aw salt

sat satw w

aw salt awsat satw w salt

K saltaw salt aw

K

C CK K

C C

K K

CC

CC

Air-Water Exchange Effect of salt

pyrene, Kaw = 10-3.32

seawater [salt]tot = 0.5 M KS = 0.30

[ ]3.32,

3.32 (0.30)(0.5) 3.32,

3.17,

10 10

10 10 10 1.4

10

StotK salt

aw salt

aw salt

aw salt

K

K

K

Air-Water Exchange Effect of co-solvents

Co-solvents increase solubility; decrease KH

,,

,

,

,

,

, 10c

v

aw mix

sat satw w

aw mix awsat satw w mix

satw mix f

aw mix aw

asatw mix

asatw

aw

i

satw

m x

K

C CK K

C C

CC

C

K K

C

K

Air-Water Exchange Effect of co-solvents

naphthalene, Kaw = 10-1.74

20% acetone solution fv = 0.2 c = 6.5

(6.5)(0.2) 1.74,

3.04,

10 10 (10 )

10

cvf

aw mix aw

aw mix

K K

K

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 = 100.16

what fraction of the chloromethane is in the bubble?

H

CH

H Cl

H

CH

H Cl

Air-Water Exchange Partition between air and water

H

CH

H Cl

molesinairmolesinair+molesinwater

a aa

a a w w

C Vf

C V C V

aa

wa

aw

Vf

VV

K

0.16

1 10.036 3.6%

39 28.0110

afi ntheair

H

CH

H Cl

Next Lecture Air-Water Exchange Kinetics

Read Chapters 18, 19, and 20