Page 902 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Appendix H: Dissolved Gases 857

TABLE H.2
Common Units for Henry’s Constant, Volatility and Solubility Forms

A B C
atm i(g) a,b mol i(g)=L(g) b mol i(g)=mol(g) b
Volatile form, H D 1
i
mol i(aq)=mol H 2 O mol i(aq)=LH 2 O mol i(aq)=mol H 2 O
atm i(g) b,c,d
2
mol i(aq)=m H 2 O
3
3
mol i(aq)=LH 2 O e mol i(aq)=m H 2 O e mg i(aq)=LH 2 O f
Solubility form, H S 3
1
atm i(g) Pa atm i(g)
a
Alberty and Silbey (1992).
b
Brennan et al. (1998).
c
Ashworth et al. (1988).
d
Yaws (1999).
e
Sander (1999) [note that the second citation (3,B) is the official SI unit].
f
Units adopted for this text.
For engineering purposes, the Equation H.11 form of D atm m 3
H CHCl 3 ,25 C ¼ 0:0041011
Henry’s law, i.e., 3C, is recommended here, with units as mol
S
given, i.e., H ¼ (mg i=LH 2 O=atm i). Reasons include (1) a
1
large number of problems are in terms of concentrations in 2. Expand the units to distinguish the solute (dissolved
mg=L and pressure in atmospheres (or kPa), and (2) tables of gas) from the solvent (water), i.e., place a label on
solubility data in mg=L and usually for 1.0 atmosphere partial each unit, and round off value given,
pressure of gas gives an associated Henry’s constant directly.
3
atm CHCl 3 m H 2 O
H D ¼ 0:0041
CHCl 3, 25 C
mol CHCl 3
H.2.4 CONVERSIONS OF UNITS FOR HENRY’S CONSTANT
3. Apply chain-of-conversions
To convert from a given set of units for Henry’s constant to
another set, the chain of conversions approach will always atm CHCl 3 m H 2 O
3
work. As a caution, because conversions may be tedious, H D CHCl 3, 25 C ¼ 0:0041
mol CHCl 3
verification should be a part of the process. This can be
done most easily by testing the conversion for a gas that is mol CHCl 3 g CHCl 3
3
found in published literature in both the source units and the 119:377 g CHCl 3 10 mg CHCl 3
3
target units. Carbon dioxide and dissolved oxygen are 10 LH 2 O
examples of gas species that are likely to be found in several m H 2 O
3
forms of units. Another is chloroform. Table H.3 gives the
numerical values for each compound in the various units from 4. After canceling the terms,
Table H.2.
LH 2 O
H D
CHCl 3 ,25 C ¼ 0:0041 atm CHCl 3 119:377 mg CHCl
H.2.4.1 Procedure for Conversion of Units 3
for Henry’s Constant 5 atm CHCl 3 LH 2 O
¼ 3:43 10
To convert from one set of units to another, the mg CHCl 3
‘‘chain-of-conversions’’ principle always works. The proced-
ure is illustrated in Examples H.5 and H.6, with the target 5. Converting to H S
CHCl 3
S
units being H in mg i (aq)=LH 2 O=atm i (g).
i
1
H S
CHCl 3 ,25 ¼ D
H CHCl 3 ,25 C
Example H.5 Conversion of Henry’s
constant as H to H i S 1
D
i
¼ atm CHCl 3 LH 2 O
3:43 10 5
1. Obtain a Henry’s constant from a literature source. mg CHCl
3
Consider, for example, the Henry’s constant for
mg CHCl
chloroform, CHCl 3 , MW (CHCl 3 ) ¼ 119.377, at ¼ 2:9 10 4 3 : atm CHCl 3
258C from Yaws (1999, p. 407), LH 2 O