Chemistry Reference
In-Depth Information
Figure 8.9
Formation of Caves
(a) Huge underground chambers,
such as the Luray Caverns in the
Blue Ridge Mountains of Virginia,
are formed over eons by the reaction
of carbon dioxide dissolved in water
with solid limestone, (Note
the people near the bottom center of
the picture.) (b) Water containing
calcium hydrogen carbonate,
dripped from the
ceiling of the limestone cavern and
deposited solid calcium carbonate,
when the concentration of
carbon dioxide was low. A droplet
hanging from the ceiling formed a
tiny portion of a stalactite; a droplet
that hit the floor formed a tiny
portion of a stalagmite.
CaCO
3
.
Ca(HCO
3
)
2
,
CaCO
3
,
(a)
(b)
Carbon dioxide, an acidic anhydride, can react with a base to form an acid
carbonate or a carbonate:
CO
2
(g)
NaOH(aq) £ NaHCO
3
(aq)
CO
2
(g)
2 NaOH(aq) £ Na
2
CO
3
(aq)
H
2
O(
/
)
The base either partially or totally neutralizes the carbon dioxide.
● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●
Carbon dioxide present in relatively high concentration in water can dis-
solve insoluble carbonates to yield soluble acid carbonates:
ITEM OF INTEREST
CO
2
(g)
H
2
O(
/
)
CaCO
3
(s) £ Ca(HCO
3
)
2
(aq)
The reaction of limestone with water containing carbon dioxide
in relatively high concentration can form natural caves, such as Luray
Caverns in Virginia (Figure 8.9). If the carbon dioxide concentration is
lowered, the reverse reaction can occur:
(CaCO
3
)
Ca(HCO
3
)
2
(aq) £ CO
2
(g)
H
2
O(
/
)
CaCO
3
(s)
Thus, water dripping from the ceiling of a cavern can deposit a
tiny particle at a time, and over long periods can form stalactites and
stalagmites.
CaCO
3
Acid carbonates undergo double substitution reactions with either acids or
bases, neutralizing them:
NaHCO
3
(aq)
HCl(aq) £ NaCl(aq)
H
2
O(
/
)
CO
2
(g)
NaHCO
3
(aq)
NaOH(aq) £ Na
2
CO
3
(aq)
H
2
O(
/
)
These types of reactions are summarized in Figure 8.10.
