On the 1H NMR spectra of weak electrolytes under the influence of strong electrolytes at low concentrations

• Published in: Journal of molecular liquids 2023-07, Vol.382, p.121932, Article 121932
• Main Author: Madeira, Pedro P.
• Format: Article
• Language: English
• Subjects: Chemical equilibrium; Electrostatic forces; Hofmeister effect; Strong electrolytes; Weak electrolytes
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2023.121932

[Display omitted] •Strong electrolytes perturb the auto-dissociation of water, releasing H+ or OH–.•At low salt concentrations, this effect modulates the co-solute properties.•Those salts releasing H+ suppress the dissociation of weak acids and are neutral to weak bases.•Those salts releasing OH– suppress the dissociation of weak bases and are neutral to weak acids. Physical chemistry has yet to provide a convincing explanation for the many distinct ways the cosolute's properties are perturbed when under the field of action of salt ions. For that reason, a systematic and gradual approach to the problem was sought, with the present work being a step in that direction. Thus, acetic acid and n-butylamine were selected as simple models for the charged carboxyl and amine groups in more complex solutes, like proteins. The influence of the gradual addition of inorganic salts on these compounds' proton nuclear magnetic resonance spectra was analyzed. The salt concentration varied from 0.01 to roughly 100 mmol.L−1. The reported results suggest that at a low salt concentration ( divalent > monovalent. Therefore, the experimental facts herein reported show that the effect of salt ions at low concentrations upon the properties of other solutes can be rationalized by conventional chemical concepts, in which chemical equilibrium plays an important role. Furthermore, the results strongly support the classical interpretation of salt ions, which are charged bodies that, in solution, exert chiefly electrostatic forces.