Aqueous Solution Properties¶

Mean salt activity coefficient¶

The mean salt activity coefficient is calculated from the activity coefficients of the ions,

\[ \ln\left(\gamma_{\pm}^{*,m}\right)=\frac{\nu_{+}}{\nu}\ln\left(\gamma_{+}^{*,m}\right)+\frac{\nu_{-}}{\nu}\ln\left(\gamma_{-}^{*,m}\right) \]

In this equation \(\nu_{+}\) and \(v_{−}\) are the stoichiometric coefficients of the cations and anions of the salt, while \(\nu\) stands for the sum of these stoichiometric coefficients. With the mean salt activity coefficient the real behavior of a salt can be calculated and it can, e.g. be used for the calculation of electromotoric forces EMF.

Osmotic coefficient¶

The osmotic coefficient represents the reality of the solvent in electrolyte systems. It is calculated by the logarithmic ratio of the activity and mole fraction of the solvent:

\[ \Phi=-\frac{\ln a_{i}}{M_{s}\sum_{ion}m_{ion}} \]

Freezing point depression¶

The Schröder and van Laar equation is used:

\[ \frac{\ln a_{i}}{\left(1-\left(T_{m,i}/T\right)\right)}=\frac{\triangle_{m}h_{i}}{RT_{m,i}} \]

On the right hand side of the equation a constant factor is achieved, while on the left hand side the activity depends on temperature and composition. For a given composition the freezing point of the system can be calculated iteratively by varying the system temperature. The best way to do this is by starting at the freezing point of the pure solvent. This equation also allows calculating the freezing point of mixed solvent electrolyte systems.