An investigation of proton solvation in aqueous sulfuric acid solutions based on the 1700 cm⁻¹ absorption band in their IR spectra

Conclusions

• 1. Following the method of frustrated total internal reflection and working at 30‡C, we have measured the change in the optical density of the H-O-H group deformation vibration band in the spectrum of the hydrated protons in aqueous 4.96–98.49% H₂SO₄ solutions. In dilute acid solutions the proton is firmly solvated with two water molecules to form the (H₂O... H...OH₂)⁺ ion; in more concentrated solutions there is not enough water to permit each dissociated proton to solvate in this way, and solvation leads to the formation of (H₂O...H... OR)⁺ ions in which OR is some part of the acid molecules.

• 2. The measured values of the optical density have been used to calculate equilibrium concentrations of the H₅O ⁺₂ and H₃O₂R⁺ ions in 60.36–85.70% H₂SO₄ solutions. In aqueous H₂SO₄ solutions the point of the H₃O₂R⁺+H₂O ⇄ H₃O ⁺₂ +OR equilibrium is not completely displaced toward the right (OR is a part of the acid molecule).