174
C. ALBERS
except the hydroxyl ion and base stands for the sum of all cations except
the hydrogen ion. This “medical” definition of acids and bases does not
seem to be in accord with the proper chemical definition. This disagreement, however, turns out to be formal rather than substantial, as pointed
out by Siggaard-Andersen (1965). The medical definition was adopted
several decades ago by van Slyke and his group who contributed most
to our basic knowledge of the acid-base balance in mammals. Because
much more is known about the acid-base balance in warm-blooded animals, some basic facts about the acid-base balance in mammals will be
included in this chapter. The question of whether or not these facts are
pertinent to the acid-base balance of fish has to be left open in many
cases. It is the hope of the author that his description of the acid-base
balance will prompt other investigators to fill in the gaps in this really
fascinating field of comparative physiology and biochemistry.
11. BASIC CONCEPTS OF PHYSICAL CHEMISTRY
A. The Dissociation of Water and the Definition of pH
Water molecules are dissociated into hydrogen ions and hydroxyl ions
to a very small extent. The ionic product of water
Kw = [H+][OH-]
(1)
is of the order of lVI4, depending on the temperature and the ionic
strength of the solution. The hydrogen ion is normally present in the
hydrated form H30, but for the sake of simplicity we shall stick throughout this chaptcr to the more convenient form of denoting the hydrogen
ion as H’. Since in pure water hydrogen ions equal hydroxyl ions the
concentration of H+ is ! 1 KlV or about
molelliter. If [ H I is changed
by adding acids or bases, the concentration of. hydroxyl ions [OH-]
changes inversely according to Eq. (1). For instance, if we have a 0.1 N
HCl solution, [H’] = 10-1 and [OH-] =
The classic laws of thermodynamics describing the reactions of ions
are valid only for ideal, infinitely diluted solutions. Very dilute solutions
may be regarded as nearly ideal solutions. In all practical cases, however,
the thermodynamic laws are valid only if activities rather than conccntrations are used. The activity is obtained by multiplying the concentration by the so-called activity coefficient f. For hydrogen ions we have
u,,+ = [H’] f,,,. Although for practical purposes the distinction between
the concentration and the activity of an ion is important, we shall
(for K , = l O - I 4 ) .
C. ALBERS
except the hydroxyl ion and base stands for the sum of all cations except
the hydrogen ion. This “medical” definition of acids and bases does not
seem to be in accord with the proper chemical definition. This disagreement, however, turns out to be formal rather than substantial, as pointed
out by Siggaard-Andersen (1965). The medical definition was adopted
several decades ago by van Slyke and his group who contributed most
to our basic knowledge of the acid-base balance in mammals. Because
much more is known about the acid-base balance in warm-blooded animals, some basic facts about the acid-base balance in mammals will be
included in this chapter. The question of whether or not these facts are
pertinent to the acid-base balance of fish has to be left open in many
cases. It is the hope of the author that his description of the acid-base
balance will prompt other investigators to fill in the gaps in this really
fascinating field of comparative physiology and biochemistry.
11. BASIC CONCEPTS OF PHYSICAL CHEMISTRY
A. The Dissociation of Water and the Definition of pH
Water molecules are dissociated into hydrogen ions and hydroxyl ions
to a very small extent. The ionic product of water
Kw = [H+][OH-]
(1)
is of the order of lVI4, depending on the temperature and the ionic
strength of the solution. The hydrogen ion is normally present in the
hydrated form H30, but for the sake of simplicity we shall stick throughout this chaptcr to the more convenient form of denoting the hydrogen
ion as H’. Since in pure water hydrogen ions equal hydroxyl ions the
concentration of H+ is ! 1 KlV or about
molelliter. If [ H I is changed
by adding acids or bases, the concentration of. hydroxyl ions [OH-]
changes inversely according to Eq. (1). For instance, if we have a 0.1 N
HCl solution, [H’] = 10-1 and [OH-] =
The classic laws of thermodynamics describing the reactions of ions
are valid only for ideal, infinitely diluted solutions. Very dilute solutions
may be regarded as nearly ideal solutions. In all practical cases, however,
the thermodynamic laws are valid only if activities rather than conccntrations are used. The activity is obtained by multiplying the concentration by the so-called activity coefficient f. For hydrogen ions we have
u,,+ = [H’] f,,,. Although for practical purposes the distinction between
the concentration and the activity of an ion is important, we shall
(for K , = l O - I 4 ) .