>>16749426
Both are unknown. Debbie Huckle made a theory about charges in a solution inducing some dipoles or some such and for dilute solutions we can get activity coefficients as a function of ironic strength which is a measure of how many charges are present. Now this kind of theory didn't work with concentrated salt solitons so Pitzer made a model with so many binary interaction coefficients it'll fit the data if you can get it. These parameters can have a physical meaning but because they come from experiments they don't count as a kind of explanation but it's just the best functional form for the curve fitting exercise though really the Dortmund data bank run will happen once the thermodynamic relations become applied to thin plate smoothing splines of some Gibbs energy.

Plus it's not even 35% at all temperatures.