
Vol.
27 No. 3
MayJune 2005
Equilibria in Solution: A Software Aid
Igor V. Sukhno, Vladimir Y. Buzko, and Leslie D. Pettit, members
of the task group for the project titled Ionic Strength Corrections
for Stability Constants (project
#20000031500) are reporting the availability of AqSolutions,
a software package of programs for the quantitative treatment
of equilibria in solution.
AqSolutions consists of a controlling program (Aq_Solutions.exe). This gives access to a suite of programs which, it is planned, will be regularly extended and updated. Programs are included for the quantitative correction of stability constants for ionic strength changes and temperature changes, for the calculation of gas solubilities, for speciation and for titration simulations.
SIT corrects stability constants for changes in ionic strength using SIT (Specific Interaction Theory) and to estimate SIT parameters with full statistics. The program contains an editable database of published SIT parameters. It also provides routines to interconvert molarities (c) and molalities (m), and lg K_{c} and lg K_{m}. A version of the SIT program to correct stability constants for changes in seawater salinity and in electrolyte mixtures (fluids) is in preparation.
Electrolytes calculates electrolyte activity coefficients, osmotic coefficients and the activity of water using Pitzer and the LinTsengLee equations. The program can also be used to calculate ionic activity coefficients using the MilleroPitzer method. A version of the Electrolytes program, which will calculate the ionic activity coefficients for the most important ions in seawater is in preparation.

Acidbase calculates the composition of acidbase systems at equilibrium in electrolyte solutions and seawater. It will also calculate H^{+} activity coefficients for correction of pa_{H} to p[H^{+}] in different ionic media. The concept of apparent equilibrium constant is used to calculate equilibrium constants for more than 260 mono and polycarboxylic acids with background ions. A version of the Acidbase program to calculate the H^{+} activity coefficient in seawater at different salinity (chlorinity), and at different temperatures, is in preparation.
Temperature effects is an aid for the study and prediction of the temperature dependence of lg K using eight thermodynamic equations:
—Van’t Hoff equation
—Isobar equation
—Extended Isobar equation
—ClarkeGlew equation
—Extended ClarkeGrew equation
—DQUANT equation
—Valentiner equation
—BlandamerRobertsonScott equation
Full statistics are included.
Gas solubility calculates O_{2} solubility in water, 22 electrolyte solutions, natural fluids, and seawater as a function of temperature, concentration, and salinity. A program to calculate the solubilities of other gasses is in preparation.
Speciation calculates and displays
species distribution curves for complexes (including insoluble
species). Speciation can be displayed as a function of pH,
pL (any reactant), or total reactant concentration, and as
either percentages or species concentrations (log values).
When insoluble phases are present, lg S values may
also be plotted. Both graphs and tables of numeric values
may be displayed, printed, or saved to disk. The sensitivity
of speciation curves to errors in lg K values can be
demonstrated graphically.
Titration Simulations simulates ML titration curves in real time and display speciation dynamically. Species L, HL, H2L, ML, ML2, MHL, and MH1L may be included and stability constants adjusted in real time. Titration curves, speciation curves, and picharts are calculated in real time.
Other programs are in preparation and will be included at a later date. These include programs for electrode calibration, for properties of individual electrolyte solutions, and their mixtures (solubility, density, viscosity, ΔC_{p}, freezingpoint, boilingpoint, surface tension), as well as for water properties as a function of temperature, pressure, and concentration of individual electrolytes or electrolyte mixtures (a_{w}, pK_{w}, ΔH_{w}, ΔC_{p}, viscosity, density).
A preliminary version of the suite of programs may be downloaded from <www.iupac.org/projects/2000/20000031500.html> or from <www.acadsoft.co.uk>.
Please send questions and comments to the authors. Igor V. Sukhno <sukhno@chem.kubsu.ru> and Vladimir Y. Buzko <buzko@chem.kubsu.ru> are both from the Department of Chemistry of the Kuban State University, in Krasnodar, Russia. Leslie D. Pettit <pettit@acadsoft.co.uk>, Academic Software, Yorks, UK, is task group chairman.
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