576 CYCLES OF ORGANIC AND INORGANIC SUBSTANCES 



to 10"*^- ^ which is of the expected order of magnitude; the cause 

 of the little difference may be that CoOOH is present as a solid 

 solution, perhaps with FeOOH 

 Nickel. The equilibrium 



XiO. (s) + 2H.0 + 2e- ^ Xi(OH), (s) + 20H-. log K = 16.6 



would indicate that Xi(0H)2 (s) is stable, but not XiO-:, at the pH 

 and pE of sea water. On the other hand, the equilibrium 



Xi(0H)2 (s) + 2H+ ^ Xi++ + 2HoO, log K = 10.8 



would give log [Ni++] = 10.8 + 0.8 - (2 X 8.1) = -4.6, whereas 

 the analyses of sea water are from —7.0 to -8.9. So, neither 

 Ni(0H)2 seems to exist at equilibrium as solid phase. With XiCOa 

 as solid, (solubility product given as 10"^), much too high Ni 

 concentrations will also be calculated. It is possible that the 

 concentration of Xi++ is determined by equilibria solid solution/ 

 aqueous solution. 



Copper. From Nasanen and Tamminen (1949) we may take 

 (25°C, zero activities) : 



CuO (s) + H.O ^ Cu++ + 20H- log K = -19.66 



Cu(OH)i.5(S04)o.25 (s) ^ CU++ + I.5OH-+O.25SO4-- log K= -17.12 



Cu(OH)i.5Clo.5 (s) ;^Cu++ + 1.50H- + 0.5C1- log A' = -17.27 



For equilibrium between the hydroxide-chloride and hydroxide- 

 sulfate, we would have 



0.5 log {CI-} - 0.25 log {SO4— } = -17.27 + 17.12 = -0.15 



By inserting the values log {CI-} = —0.26 — 0.2 = —0.46, and 

 log {SO4} = -1.55 - 0.8 = -2.35, we find the difference -0.23 

 _[- 0.59 = 0.36. This would mean that the hydroxide-chloride is 

 somewhat more stable than the hydroxide-sulfate. but the differ- 

 ence is so small that it might be changed by the temperature 

 variation of equilibria. 



For equilibrium between CuO (s) and Cu(OH)i.5Clo.5 (s), we 

 find 0.5 log {OH-} - 0.5 {CI-} = -19.66 + 17.27 = -2.39, 

 whereas the difference in sea water is 0.5 (8.1 — 14.0 + 0.46) = 

 — 2.72, Here, too, we would have a small advantage for the 

 hydroxide-chloride which may be reversed, however, if CuO enters 



