PyES-An open-source software for the computation of solution and precipitation equilibria

A new, open-source, practical, modern and multi-platform Python application for concentrations calculation (PyES - Python Equilibrium Species) was developed by re-writing and implementing the ES4, a freeware computer program originally written using the BASIC programming language. Currently PyES has two working modes, i.e., titration simulation and species distribution, and it can handle both precipitation and solution equilibria. Noteworthy, PyES is actually the only open-source software able to perform calculations at variable ionic strength, taking into account the dependence of the stability constants on it, and to take into account the error propagation to estimate the uncertainties in the calculated concentrations using those of the formation constants, solubility products and components concentrations. Various tests were performed to verify the reliability of PyES with very satisfying results. Moreover, PyES is user friendly and compatible with existing operative systems. The data analysis results can be visualized in a graphical presentation and can be easily exported as .xlsx or .csv files. PyES and the corresponding source code are available for download at htt ps://github.com/Kastakin/PyES.