Spectrophotometric investigations of aqueous solutions at elevated temperatures

Abstract

New spectrophotometric data have been obtained for the dissociation of salicylic acid (H₂L), over the temperature range 10–85°C, from which values of the first and second thermodynamic dissociation constants (K₁ and K₂ respectively) of the acid have been calculated.

The results substantiate recent conductimetric measurments of K₁, which show a shallow maximum in K₁ near 40°C. They indicate an increase in K₂ with temperature in the range considered but do not agree well with available literature values for this constant.

Discrepancies in K₂ are attributed largely to systematic errors arising from the low degree of formation of L^2–, slight chemical decomposition of this species particularly at higher temperatures, and high ionic strength in the experimental solutions. As a result of these errors it is unlikely that reliable thermodynamic data can be derived from reported determinations of K₂.