Accurate and Efficient Prediction of pK_w in Aqueous Electrolytes Using Local Electrostatic Potentials

Area of Science:

• Physical Chemistry
• Electrochemistry
• Computational Chemistry

Background:

• The ion product of water (Kw) in aqueous electrolytes shows significant concentration-dependent variations.
• Existing models like the Pitzer model fail to accurately describe these trends, especially at high ion concentrations.

Purpose of the Study:

• To provide a molecular interpretation for the concentration-dependent behavior of pKw.
• To develop a novel, computationally efficient method for predicting the dissociation constant (Kw) in electrolytes.

Main Methods:

• Molecular dynamics simulations to sample local water configurations and determine local electrostatic potentials.
• Utilizing experimentally measured pKw values for calibration.
• Developing a predictive model based on the local electrostatic potential of water oxygen atoms.

Main Results:

• Accurate prediction of concentration-dependent pKw trends using the new molecular approach.
• The method's efficiency relies on sampling local configurations and a minimal set of experimental data.
• Demonstrated extensibility to various salt compositions.

Conclusions:

• The local electrostatic potential, influenced by nearest water neighbors, is key to understanding pKw variations.
• The developed method offers a molecular insight into electrolyte behavior.
• Provides a foundation for designing electrolytes with tunable physicochemical properties, including pKw.