1260 WATER CHEMISTRY
TABLE 2B
First acidity constant: H 2 CO 3 HCO 3 HK 1 3
23{}{}
{}*HHCO
HCOK′ 1 3 T
23{}[]
[]*HHCO
HCOcK T
13
23[][]
[]*HHCO
HCOTemp., °CMedium→ 0 Seawater, 19% Cl Seawater 1 M NaClO4log K log K 1 — logcK 1
0 6.579a 6.15b ——
5 6.517a 6.11b 6.01e —
10 6.464a 6.08b ——
14 — — 6.02f —
15 6.419a 6.05b ——
20 6.381a 6.02b ——
22 — 6.00c 5.89c —
25 6.352a 6.00b, 6.09d — 6.04g
30 6.327a 5.98b ——
35 6.309a 5.97b ——
40 6.298a ———
50 6.285a ———a H. S. Harned and R. Davies, Jr., J. Amer. Chem. Soc. , 65, 2030 (1943).
b After Lyman (1956), quoted in G. Skirrow, Chemical Oceanography, Vol. I, J. P. Riley and G.
Skirrow, Eds., Academic Press, New York, 1965, p. 651.
c A Distèche and S. Distèche, J. Electrochem. Soc. , 114, 330 (1967).
d Calculated as log (K 1 /fHCO3) as determined by A. Berner, Geochim. Cosmochim. Acta, 29, 947 (1964).
e D. Dyrssen, and L. G. Sillén, Tellus, 19, 810 (1967).
f D. Dyrssen, Acta Chem. Scand. , 19, 1265 (1965).
g M. Frydman, G. N. Nilsson, T. Rengemo, and L. G. Sillén, Acta Chem. Scand. , 12, 878 (1958).
Ref.: Stumm, W. and J. Morgan, Aquatic Chemistry, Wiley-Interscience, New York, 1970, p. 148.TABLE 2A
Equilibrium constant for CO 2 solubility
Equilibrium: CO 2 (g) aq H 2 CO 3
Henry’s law constant: K [H 2 CO 3 ]/pCO 2 (M.atm–1)Temp., C → 0 Medium, 1 M NaClO^4 Seawater, 19% C1––log K –logcK –log cK
0 1.11a — 1.19a
5 1.19a — 1.27a
10 1.27a — 1.34a
15 1.32a — 1.41a
20 1.41a — 1.47a
25 1.47a 1.51c 1.53a
30 1.53a — 1.58a
35 — 1.59c —
40 1.64b ——
50 1.72b ——a Values based on data taken from Bohr and evaluated by K. Buch,
Meeresforschung, 1951.
b A.J. Ellis, Amer. J. Sci. , 257, 217 (1959).
c G. Nilsson, T. Rengemo, and L. G. Sillen, Acta Chem. Sand. , 12, 878 (1958).
Ref.: Stumm, W. and J. Morgan, Aquatic Chemistry, Wiley-Interscience,
New York, 1970, p. 148.It is difficult to generalize about rates of precipita-
tion and dissolution other than to recognize that they are
usually slower than reactions between dissolved species.
Data concerning most geochemically important solid-solu-
tion reactions are lacking, so that kinetic factors cannot be
assessed easily. Frequently the solid phase initially formed
is metastable with respect to a thermodynamically more
stable solid phase. Relevant examples of such metastabil-
ity are the formation of aragonite under certain conditions
instead of calcite, the more stable form of calcium car-
bonate, and the over-saturation of quartz in most natural
waters. This over-saturation persists due to the extremely
slow establishment of equilibrium between silicic acid and
quartz.
The solubilities of most inorganic salts increase with
increasing temperature. However, a number of compounds
of interest in natural waters (e.g. CaCO 3 , CaSO 4 ) decrease in
solubility with increasing temperature. The dependence of
solubility on pressure is very slight but must be considered
for the extreme pressures encountered at ocean depths. For
example, the solubility product of CaCO 3 will increase by
approximately 0.2 logarithmic units for a pressure of 200
atmospheres (ca. 2000 meters).C023_002_r03.indd 1260C023_002_r03.indd 1260 11/18/2005 1:32:07 PM11/18/2005 1:32:07 PM