Geology Reference
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of 4-chlorophenol (K
0
¼
10
9.18
). Annotate the plot to show the
equilibrium pH of the groundwater.
(iii) Calculate the equilibrium pH of rainwater in equilibrium with
CO
2(g)
at a partial pressure of 0.00035 atm (hint: the charge
balance equation can be approximated by {H
1
}
¼
{HCO
3
}).
log K
ð
288K
Þ
CO
2
ð
g
Þ
þ
H
2
O
Ð
H
2
CO
3
1
:
34
H
2
CO
3
Ð
H
þ
þ
HCO
3
6
:
35
HCO
3
Ð
H
þ
þ
CO
2
10
:
33
3
(iv) Construct a pe-pH diagram for selenium species present in
natural waters. Assume that the total dissolved concentration
of selenium is 10
6
mol L
1
. From the diagram, predict the
major selenium species in
(i) oxic and acidic waters (pe
B
10, pH 4-7)
(ii) oxic and alkaline waters (pe
B
10, pH 47)
(iii) anoxic groundwaters (pe
B
3, pH 4-8).
For each set of conditions, outline the implications for sorption
onto solid phases.
log K(298 K)
SeO
2
4
þ
4H
þ
þ
2e
Ð
H
2
SeO
3
þ
H
2
O
41.40
SeO
2
4
þ
3H
þ
þ
2e
Ð
HSeO
3
þ
H
2
O
38.76
SeO
2
4
þ
2H
þ
þ
2e
Ð
SeO
2
þ
H
2
O
30.26
3
H
2
SeO
3
Ð
HSeO
3
þ
H
þ
2.75
HSeO
3
Ð
SeO
2
3
þ
H
þ
8.50
H
2
SeO
3
þ
4H
þ
þ
4e
Ð
Se
ð
s
Þ
þ
3H
2
O
48.58
HSeO
3
þ
5H
þ
þ
4e
Ð
Se
ð
s
Þ
þ
3H
2
O
51.33
SeO
2
3
þ
6H
þ
þ
4e
Ð
Se
ð
s
Þ
þ
3H
2
O
59.83
Se
ð
s
Þ
þ
2H
þ
þ
2e
Ð
H
2
Se
ð
aq
Þ
3.52
Se
ð
s
Þ
þ
H
þ
þ
2e
Ð
HSe
7.32
H
2
Se
Ð
HSe
þ
H
þ
3.80
(v) Draw, describe, and compare the concentration profiles of the
chemical species of manganese, iron, arsenic, and phosphorus
likely to be found in the solid and solution phases of unmixed
sediments at the bottom of a seasonally anoxic, eutrophic
freshwater lake during (i) summer and (ii) winter.
