1
1
The atmosphere on a distant planet is entirely
carbon dioxide at a pressure of 1520 torr (2 Earth
atmospheres).
What would the pH of a lake on this
planet be if both the hydronium ion and hydrogen
carbonate concentrations were determined by the
dissolved carbon dioxide?
Henry’s law constant for CO
2
= 0.030 M/atm.
pK
1
for carbonic acid (H
2
CO
3
) = 6.37
[CO
2
] = 1000 [H
2
CO
3
]
If you mastered the information presented on Monday, this problem,
which was asked by a student in class, should
be “a piece of cake”!
A) 5.3
B) 3.1
C) 3.5
D) 4.1
E) 8.5
2
x

6.0x10
x
10
x
x
x

M
10
6.0
x
x
x

0
0
atm)
M/atm)(2
(0.030
1000
1
HCO
O
H
0
H
CO
H
5

2
6.37

5


3
3
2
3
2
x
If you neglect x in the denominator, you
find x = 5.1
x
10
6
and pH = 5.29.
Note 6.0
x
10
5
/ 5.1
x
10
6
= 11.8
If you do the quadratic equation thing, you
find x = 5.3
x
10
6
and pH = 5.28.
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