THE PHYSICAL CHEMISTRY OF SEA WATER 577 



some solid solution, like the "manganite." With the equilibrium 

 constant at 25°C, we would estimate log [Cu++] = —17.27 + 

 (1.5 X 5.9) + (0.5 X 0.46) + 0.8 = -7.4. An approximately 

 equal amount would be present as CuOH+, and would make the 

 estimated log [Cujtotai = —7.1. The analytical values are between 

 — 5.8 and —8.4, which is still of the correct order of magnitude. 

 Some other copper complex may be present, such as Cu(0H)2, but 

 the chlorocuprate(I) like CuCU" would not seem to be significant 

 at equilibrium. 



Lead. At 25 °C we have 



Pb02 (s) + 4H+ + SO4— + 2e- ^ PbS04 (s) + 2H2O, log K = 57.0 

 Now, in sea water, the expression 



-(4 log {H + } + log {SO4-} + 2 log {e-\) 



= (4 X 8.1) + 1.5 + 0.8 + (2 X 12.4) = 59.7 



Thus, PbOo seems to be stable but not PbS04. The formation of 

 Pb02 may be further favored if it forms solid solutions with some 

 other phase, such as Mn02. 

 From the equilibrium 



PbO. (s) + 4H+ + 2e- ^ Pb++ + 2H2O, log K = 49.2 



we find 



log [Pb++] - 49.2 + 0.8 - (4 X 8.1) - (2 X 12.5) - -7.4 



According to Olin (1960), for 



Pb++ + H20;^PbOH+ + H+, logi^ = -7.9 (25°C, 3MNaC104) 



We may then estimate that in sea water of pH = 8.1, roughly 

 equal concentrations of Pb"*""^ and PbOH+ are present. Moreover, 

 [PbCl"^] may be two to six times [Pb-+], so that altogether [Pbjtotai 

 would be lO-'^Ho IQ-'^'^M. On the other hand, PbOo at equilibrium 

 may be present not as the pure substance but in solid solution 

 with, say, MnOo. Since Mn is 10- '^ times more abundant than Pb, 

 the activity Pb02 (s) may then easily be only 10~^ to 10~-, and 

 the [Pb-+], etc., and [Pb],otai calculated should be multiplied by 

 this factor. The total concentrations reported in sea water, from 

 ;[Q-8 ^Q 10~^-^M are of the right order of magnitude. 



