In a message dated 9/28/2001 2:07:43 PM Eastern Daylight Time, 
squi...@silver.nxlkhost.com writes:


> Roger,
> we are already talking about very dilute systems.  10ppm is one part per 
> 100,000.  So ionic impurities take on greater proportionate values.. 
> Stephen 
> 

Stephen: No, the more dilute a solution, the more ideally it behaves. That's 
why we're in very good shape using solution theory to make these kinds of 
estimates. Even at concentrations which are significantly greater than dilute 
(16,000 PPM Ag+, for example), solubility product calculations are still 
reasonably accurate. In addition, thermodynamic "theory" holds for 
concentrated solutions. The only difference is that one has to obtain values 
(usually through experimentation, but sometimes approximated through 
thermodynamic and other types of modeling) for the activity coefficients in 
question. Complex systems, however, are another story. Feel free to wring 
your hands when it comes to solving a system of equations for them. Roger