Preferred Citation: . The Oceans, Their Physics, Chemistry, and General Biology. New York:  Prentice-Hall,  c1942 1942. http://ark.cdlib.org/ark:/13030/kt167nb66r/

 
Chemistry of Sea Water

Solubility of Salts in Sea Water

The solubility of calcium carbonate in sea water has been examined in some detail, but relatively little is known about the other constituents. Because of the complex nature of sea water and the effect of other ions upon the activity of any one, the solubility product of a single salt in distilled water cannot be applied to sea water. Cooper (1937b) considers that most of the iron in sea water is not in true solution, but is present in some colloidal form, as the solubility product for the hydroxide is

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extremely small. Wattenberg and Timmermann (1938) studied the solubilities of magnesium and strontium carbonates and magnesium hydroxide in sea water. The data in table 42 are from their work. It is interesting to note the great increase in the apparent solubility products in sea water, which is due to the reduced activity of the participating ions. For comparison, the ionic products for sea water (19.00 ‰ Cl, ϑ = 20°) at pH 8.2 have been computed. The apparent supersaturation of the calcium carbonate is discussed in the preceding pages. The ionic products of the other salts do not approach their solubility products. At pH higher than 9.0 the ionic product of Mg(OH)2 will exceed the solubility product, and hence removal of CO2 may result in precipitation of magnesium hydroxide as well as the carbonates.

Thompson and his co-workers (for example, Igelsrud and Thompson, 1936) have carried out extensive phase-rule studies of solutions containing some of the salts in sea water, but so far they have not extended their investigations to natural water.

Some indication of the great solubility of the major constituents is afforded by data on the separation of salts when sea water is frozen (p. 217). Somewhat similar data may be obtained from the evaporation studies by Usiglio (Thompson and Robinson, 1932), which again bring out the fact that sea water is far from saturated with most of the constituents.

THE SOLUBILITY PRODUCTS OF CERTAIN SALTS IN DISTILLED WATER AND SEA WATER (From Wattenberg and Timmermann, 1938)
Salt K Distilled water K' Sea water S = 35 ‰, ϑ = 20° Ionic product Cl = 19.0 ‰, ϑ = 20° pH = 8.2
CaCO3 0.5 × 10− 3 50 × 10− 3 270 × 10− 3
MgCO33H2O 0.1 × 10− 4 3.1 × 10− 4 0.14 × 10− 4
SrCO3 0.3 × 10− 9 500 × 10− 9 39 × 10− 9
Mg(OH)2 1 × 10− 11 5 × 10− 11 0.02 × 10− 11
Chemistry of Sea Water
 

Preferred Citation: . The Oceans, Their Physics, Chemistry, and General Biology. New York:  Prentice-Hall,  c1942 1942. http://ark.cdlib.org/ark:/13030/kt167nb66r/