Agriculture Reference
In-Depth Information
The equilibrium is [H
3
O
+
]
[HCO
−
]. Taking this and our carbon dioxide
=
molar concentration yields
[HCO
3
−
][H
3
O
+
]
CO
2
[H
3
O
+
]
2
10
−
7
K
a
1
=
4
.
3
×
=
=
1
.
2
×
10
−
5
[H
3
O
+
]
2
10
−
12
=
5
.
2
×
[H
3
O
+
]
10
−
6
M
=
2
.
3
×
Or, since pH is the negative logarithm of the molar concentration of hydronium
ions, the pH of the droplet is 5.7.
If the concentration of CO
2
in the atmosphere increases to the very reasonable
estimate of 400 ppm, what will happen to the pH of “natural rain”?
The new molar concentration would be 3.4
10
−
2
mol L
−
1
atm
−
1
×
×
10
−
5
M, so
0.000400 atm
=
1.4
×
[H
3
O
+
]
2
1
10
−
7
4
.
3
×
=
.
4
×
10
−
5
[H
3
O
+
]
2
10
−
12
=
5
.
8
×
[H
3
O
+
]
10
−
6
M
=
2
.
4
×
Thus, the droplet pH would decrease to about 5.6. That is, the new pH is
−
log[H
3
O
+
]
10
−
6
]
5.6. This means that the incremental
increase in atmospheric carbon dioxide can be expected to contribute to greater
acidity in natural rainfall. This increase in acidity (decrease in pH) is actually
less than 0.1 pH units due to rounding. However, considering this would take
place throughout the lower portion of the entire Earth's atmosphere, it is quite
significant. Also, keep in mind that pH is a log scale.
Most of the concern for acid rain has rightly been concerned with compounds
other than CO
2
, notably oxides of sulfur and nitrogen, that are released to
the troposphere. These compounds can dramatically decrease the pH of rain.
However, the increase in CO
2
means that the pH of rainfall, which is not neutral
to begin with, can adversely affect fish and wildlife in and around surface waters
with even lower concentrations of sulfur and nitrogen compounds. Thus, as CO
2
builds up in the atmosphere, there will be a concomitant increase in rainfall acidity
if all other factors remain constant (e.g., concentrations of sulfur and nitrogen
compounds do not continue to decline).
=−
log[3.0
×
=
GLOBAL WARMING
The average temperature of Earth is difficult to measure, but most measurements
show a very small overall change that would not be detectable to humans due
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