Salicylic Acid Solubility and Thermodynamic Dissociation Constant at Various Temperatures in Water: Variable Ionic Strength Titrimetric Analysis

Abstract

Titrimetric methods were used to estimate the molar solubility and apparent acid dissociation constant (K_c) of salicylic acid in water. This was done with varied ionic strength values ranging from 0.00 to 0.75 mol·L⁻¹ and over a temperature range of 15 to 60 °C. The thermodynamic dissociation constant (as pK_a) of salicylic acid was found to be 2.985 at 25 °C. Within the measured temperature range, there was no consistent association between the pK_a of salicylic acid and the temperature. The pK_a values exhibited an inverse relationship with temperatures between 15 and 40 °C, while they showed a direct relationship with temperatures between 40 and 60 °C. Through the use of the Van’t Hoff plot, the standard thermodynamic quantities (∆H°, ∆S°, and ∆G°) for the dissociation process of salicylic acid in water were calculated. For temperatures between 15 and 30 °C, these values were determined as 3.346 kJ·mol⁻¹, − 19.99 JK⁻¹·mol⁻¹, and 9.306 kJ·mol⁻¹ respectively. For the temperature range of 45 to 60 °C, the values were calculated as − 1.499 kJ·mol⁻¹, − 27.06 kJ·K⁻¹·mol⁻¹, and 6.564 kJ·mol⁻¹. The heat of solution (∆H ^°_sol ) was computed using the Van’t Hoff Isochore plot across the temperature range of 15 to 60 °C, resulting in a value of 15.03 kJ·mol⁻¹.