Chapter 1
Sea Water as an Electrolyte
F. J. Millero
1.1
Introduction
The composition of the major components of sea water has been measured by a number of researchers over the years. The relative molar concentration of the major cations (Na+, Mg2+, ci+, K+, Sr2+) and anions (Cr, SO~-, HCO;, Br-, CO~-, B(OH)4' F-) in
the major oceans has been shown to be constant. These major components of sea water contribute to the physical chemical properties of the oceans. Since the major components of sea water are constant throughout the oceans (The Marcet Principle),.it is
possible to treat ocean waters as an electrolyte solution (sea salt) with a dash of the
non-electrolyte boric acid. This simplifies the physical chemistry of sea water solutions and other natural waters. Some minor components (Si02, NO; and PO~-) that
are added to the oceans from the bacterial oxidation of plant material can also have a
minor effect on the properties of deep waters. In this chapter, I will review how one
treats sea water as a multi-component solution, and how the major components of sea
water contribute to its physical and chemical properties. First we will examine the composition of sea water and the development of salinity.
1.1.1
Composition of Average Sea Water
The composition of the major components of sea water has been measured by a number of researchers over the years (Culkin 1965; Culkin and Cox 1966; Morris and Riley
1966; Riley and Tongudai 1967; Warner 1971; Carpenter and Manella 1973; Wilson 1975).
The relative molar composition of the major cations (Na +, Mi+, Ca 2 +, K+, Sr 2 +) in the
major oceans is shown in Fig. 1.1. Within the experimental error of the measurements,
the relative composition of cations and anions is constant in the surface waters of the
oceans. The relative composition of the cations in surface and deep waters is shown in
Fig. 1.2. All the cations except Ca 2 + are independent of the depth. This is shown more
clearly in Fig. 1.3, where the concentration of ci+ normalized to a constant salinity is
shown as a function of depth. This increase in ci+ is the result of the dissolution of
CaC0 3 in deep ocean waters due to the effect of pressure on the solubility.
All of these measurements were made relative to the chlorinity (Cl) (the mass of
halides in a given mass of sea water). It is determined by titrating sea water with AgN03
Sea water + AgN03 ~ AgCI(s) + AgBr(s)
(1.1)
Sea Water as an Electrolyte
F. J. Millero
1.1
Introduction
The composition of the major components of sea water has been measured by a number of researchers over the years. The relative molar concentration of the major cations (Na+, Mg2+, ci+, K+, Sr2+) and anions (Cr, SO~-, HCO;, Br-, CO~-, B(OH)4' F-) in
the major oceans has been shown to be constant. These major components of sea water contribute to the physical chemical properties of the oceans. Since the major components of sea water are constant throughout the oceans (The Marcet Principle),.it is
possible to treat ocean waters as an electrolyte solution (sea salt) with a dash of the
non-electrolyte boric acid. This simplifies the physical chemistry of sea water solutions and other natural waters. Some minor components (Si02, NO; and PO~-) that
are added to the oceans from the bacterial oxidation of plant material can also have a
minor effect on the properties of deep waters. In this chapter, I will review how one
treats sea water as a multi-component solution, and how the major components of sea
water contribute to its physical and chemical properties. First we will examine the composition of sea water and the development of salinity.
1.1.1
Composition of Average Sea Water
The composition of the major components of sea water has been measured by a number of researchers over the years (Culkin 1965; Culkin and Cox 1966; Morris and Riley
1966; Riley and Tongudai 1967; Warner 1971; Carpenter and Manella 1973; Wilson 1975).
The relative molar composition of the major cations (Na +, Mi+, Ca 2 +, K+, Sr 2 +) in the
major oceans is shown in Fig. 1.1. Within the experimental error of the measurements,
the relative composition of cations and anions is constant in the surface waters of the
oceans. The relative composition of the cations in surface and deep waters is shown in
Fig. 1.2. All the cations except Ca 2 + are independent of the depth. This is shown more
clearly in Fig. 1.3, where the concentration of ci+ normalized to a constant salinity is
shown as a function of depth. This increase in ci+ is the result of the dissolution of
CaC0 3 in deep ocean waters due to the effect of pressure on the solubility.
All of these measurements were made relative to the chlorinity (Cl) (the mass of
halides in a given mass of sea water). It is determined by titrating sea water with AgN03
Sea water + AgN03 ~ AgCI(s) + AgBr(s)
(1.1)