Thermodynamics of proton ionization in aqueous solution I. A precision thermometric titration calorimeter ; II. Entropy titration : a calorimetric method for equilibrium constant determinations ; III. H and S values for carboxylic acid proton ionization at 25C ; IV. Site of proton ionization from adenosine
The design, construction, and calibration of a precision thermometric titration calorimeter is described. This calorimeter was tested by determining the enthalpy change for ionization of water. The result, 13.34 ±0.03 kcal/mole (standard deviation), is in exact agreement with the best literature values. This standard deviation indicates that, using this calorimeter, ΔH values can be determined with an accuracy of ±0.0.5 kcal/mole. A calorimetric procedure has been developed for the, simultaneous determination of the equilibrium constant, the enthalpy change, and the entropy change for a chemical reaction from a single titration (Entropy Titration). This procedure has been tested by determining pK, ΔH, and ΔS for proton ionization from HPO42- and HSO4-. The method has also been used to determine pK, ΔH, and ΔS values for proton ionization from Adenosine and Ribese. The resultant pK tor each system has an accuracy of about ±0.05 pK unit. Enthalpy and entropy changes for proton ionization have been determined for twenty-six carboxylic acids. The results are discussed in terms of three previous approaches (i.e. inductive, electrostatic, and the linear relation between ΔH° and ΔS°). The results are shown not to fit any of these theories well and reasons for this are proposed. An alternate explanation is proposed based on the observed fit of the carboxylic acid data to a linear ΔG° vs ΔS° plot. The site of proton ionization from adenosine is established to be the ribose moiety. It is also shown that both the 2' and 3' hydroxyl groups are necessary for this acidity to exist in aqueous solution.
College and Department
Chemistry and Biochemistry
BYU ScholarsArchive Citation
Hansen, Lee D., "Thermodynamics of proton ionization in aqueous solution I. A precision thermometric titration calorimeter ; II. Entropy titration : a calorimetric method for equilibrium constant determinations ; III. H and S values for carboxylic acid proton ionization at 25C ; IV. Site of proton ionization from adenosine" (1965). Theses and Dissertations. 8222.
Volumetric analysis, Calorimetry, Protons, Ionization, Entropy titration