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Fixing ionic strength instead of calculating it


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Is there a way to fix ionic strength for a simulation in GWB SpecE8, instead of calculating it?

I am trying to simulate seawater while fixing ionic strength at the accepted bulk value (0.697). I add all major bulk components of seawater (ex. Cl-, Mg++, Na+, etc.) to my solution, but there is of course some small error between calculated ionic strength from the major bulk components, and the accepted bulk value in seawater. I would like to fix this value so I can properly calculate the activities of all components. 

Thanks in advance!

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Hi Demetra,

The ionic strength in most modern programs is calculated from and consistent with the distribution of species in solution. There is no way to override it in SpecE8. Please note, ionic strength here is not calculated from the component (bulk) concentrations. It accounts for the presence of ion pairs or complexes like MgCl+ and MgSO4 that cause the solution to have a lower “concentration of charge” than it would if the Mg++, Cl-, and SO4-- ions were fully dissociated. In other words, in ion association theory the activity reflects the activity coefficient as well as the distribution of mass.

Hope this helps,

Brian Farrell
Aqueous Solutions LLC
 

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