Chemval project Correcting for ionic strength effects in the Chemval thermodynamic database
This report is a summary of procedures for correcting ionic strength effects during evaluation of the CHEMVAL thermodynamic database. "Ionic strength effects" is a general term used to describe how non-participating electrolytes present in the solution can affect the extent of any reaction involving ionic species, such as complex formation or precipitation. The Davies equation describes ionic strength effects reliably up to about 0.1 molal, which covers most of the systems of interest in modelling. However, difficulties arise in evaluation, particularly for complex formation constants, because experimental measurements available in the literature are generally made at high concentrations, between 1.0 and 10 molal, well beyond the range of the Davies equation or any other simple model. Models which deal with concentrated ionic solutions have parameters for the interactions of the specific ions present, and these can be used successfully for quite complex systems. Some examples are discussed and a comparison of these different procedures with experimental data is given. However, within the framework of CHEMVAL, in which a large database is being evaluated in a short time, it is not practical to await new experimental data for most of these systems. It has been decided to use a modified form of the Davies equation in which activities are taken to be constant above ionic strength I = 0.3. This has been called the Truncated Davies Equation.
Bibliographic Reference: EUR 12975 EN (1990) 29 pp., FS, ECU 5
ISBN: ISBN 92-826-1771-8
Record Number: 199011779 / Last updated on: 1994-12-02
Original language: en
Available languages: en