"Water, water everywhere
And all the boards did shrink
Water, water everywhere
nor any drop to drink."
-Samuel Taylor Coleridge
The rime of the ancient mariner
Campbell et al., Chapter 3
The body is approxamately 2/3 water. In addition, as you will see repeatedly
this semester, water is incorporated into many organic molecules.
Molecules - the next higher level of integration above atoms, generally
aggregates of atoms linked by covalent bonds. Because water is so fundamental,
we start with water as an example molecule.
H2O has covalent bonds, but there is some separation of charge, making it
a polar molecule TRANSPARENCY (Fig. 2.13)
Water is very important as a solvent, in reactions, and in temperature regulation.
As a polar solvent, it dissolves charged molecules or ions.
A small fraction of water molecules split to H+ and OH- "ions",
and if there is an excess of H+, the solution is an acid; if OH- predominates,
it is a base. The pH scale runs from 0 (acid) to 7 neutral to 14 base (alkaline).
The pH = -log [H+]. TRANSPARENCY (Fig. 3.9)
Other important properties of water:
(1) It has a very high specific heat measured in calories (1 cal is the
energy to heat water 1oC); units of energy (the "calories" you
"count" when dieting are actually kcal). In this regard, big bodies
of water can moderate the climate (cooler in summer, warmer in the winter),
the "sea climate."
(2) It has an extremely high heat of vaporization (about 540 cal/g, actually
576 at 37oC), important in body cooling via sweating and panting.
(3) It organizes matter by adhesion and cohesion and because molecules can
be hydrophilic or hydrophobic. Consider a container of Italian dressing,
where the oil floats on the watery liquid, and the oil is organized into
small spheres when the bottle is shaken well
This page was last updated 6/7/02
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