Geology Reference
In-Depth Information
4
AQUEOUS SOLUTIONS AND
THE HYDROSPHERE
The great importance of water and aqueous solutions
on the surface of the Earth barely needs pointing out.
Water is the principal agent of erosion and of the
transportation of eroded materials, either by mechani-
cal or chemical means. The world's oceans are the pri-
mary medium for sedimentation, they act as a global
chemical repository for many substances of geological
significance, and they play a crucial part in moderat-
ing the climate and supporting life on the planet (not
to mention the role water plays in living things). Water
also has important functions in the Earth's interior:
ore transport, rock alteration and metamorphism all
involve the migration of hot aqueous fluids through
the crust. The chemistry of aqueous solutions - the
subject of this chapter - is a vital factor in all these
geological processes.
A solution consists of two kinds of constituent which
are given confusingly similar names:
solute refers to the dissolved species (e.g. the salt in
a saline solution); a solution may contain several sol-
utes, such as when sodium chloride and potassium
nitrate are dissolved in the same solution. Seawater
is a complex example of such a mixed solution.
solvent refers to the medium in which the solutes
are dissolved. Aqueous solutions are those in which
water is the solvent (Latin aqua : water).
The basic jargon of solution chemistry is reviewed in
Appendix B and key terms are defined in the Glossary.
Some of the important properties of water as a solvent
are reviewed in Box 4.1.
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