Ion Pairing in Alkali Nitrate Electrolyte Solutions.

Area of Science:

• Physical Chemistry
• Thermodynamics
• Computational Chemistry

Background:

• Understanding ion-pairing in alkali nitrate solutions is crucial for predicting thermodynamic properties.
• The "law of matching water affinity" provides a framework for explaining salt behavior.

Purpose of the Study:

• Investigate the thermodynamics of alkali nitrate salt solutions, focusing on contact ion pair formation.
• Determine the ion-pairing propensity order for LiNO3, NaNO3, and KNO3.
• Evaluate the impact of electronic polarization on thermodynamic calculations.

Main Methods:

• Thermodynamic analysis of alkali nitrate solutions.
• Investigation of contact ion pair formation and spatial patterns.
• Application of Kirkwood-Buff theory to reproduce salt activity coefficients.
• Inclusion of electronic continuum correction for nonpolarizable force fields.

Main Results:

• Ion-pairing propensity follows the order LiNO3 < NaNO3 < KNO3.
• Spatial patterns of contact ion pairs differ: Li(+) interacts with one nitrate oxygen, while Na(+) and K(+) can interact with two.
• Electronic polarization is essential for accurate activity coefficient calculations for Li(+).
• Electronic continuum correction significantly improves agreement with experimental activity coefficients and salt solubility.

Conclusions:

• The study confirms the "law of matching water affinity" in alkali nitrate solutions.
• Electronic continuum correction is a promising method for developing accurate force fields for ions with high charge densities.
• Improved force fields enhance predictions of salt activity coefficients and solubility.