THE PHYSICAL CHEMISTRY OF SEA WATER 573 



Sulfate complexes may be formed by a number of bipositive ions 

 with weak OH complexing, like Mg++, Co++, with stability 

 constants around 10°-^ (see above), which would mean that (with 

 10-1-SMSO4 — ), something like 5 to 10% of the metal would be 

 sulfato complexes. With ions of higher charge, the tendency to 

 sulfate complexing increases, but so does the hydroxide complex- 

 ing. I am aware of no ion of which it can be said with certainty 

 that it exists chiefly as sulfate complexes, under the conditions of 

 sea water. 



Carbonate complexes have been studied for se\'eral cations such 

 as 1102"'""^ and Th^"*". Phosphate complexes are known to exist, in 

 more acidic solution, with Fe"'+, Al'^+, UOo++ and many others. 

 The available data do not seem to allow any certain conclusion as 

 to the extent of carbonate and phosphate complexing in our 

 equilibrium mixture. 



Finally, there remain our unknown organic compounds, of 

 concentration 10~^ to 10~^M, which may or may not be strong 

 complex formers with some of the metal ions. Like HPO4 and 

 CO3 — , the organic complexes might give the main contribution to 

 some of the elements present at very low concentrations, say 10"^ 

 or 10"'^ M, whereas their complexing with 'the major constituents 

 would not change the equilibria very much. 



Some Anion Redox Equilibria 



Halogens and S. A check on the redox equilibria of CI, Br, and 

 S shows, as might be expected, that the predominating species, at 

 the pE and pH of the ocean, must be Cl^, Br", and SO4 at 

 equilibrium. For instance, we have 



CIO3- + 6H+ + 6e- ^ CI- + 3H2O, log K = 147 2 



BrOr + 6H+ + 6e- ^ Br" + 3HoO, log K = 146.3 



IO3- + 6H+ + 6e- ^ I- + 3HoO, log i^ = 110 1 



By inserting pE = 12.5, pH = 8.1, we find the ratios [CIO3 ]/ 

 [C1-] « [Br03-]/[Br-] ^ \0-^~\ but [lOai/il"] = 10^^-. Thus, 

 whereas CI" and Br" predominate, it seems that at equilibrium 

 lOs" would be much more important species than I" in sea water. 

 Calculations show that also HIO, IQ-, ICI2", ICl, ICI3, IBr2~, 



