cven 4424 environmental organic chemistry lecture 7 sorption of neutral organic compounds to...
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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
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
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 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 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