Dissociation Constants of Acetic Acid in 15 W/W % 2-Propanol/Water Solvent from 5 to 35 Oc at Ten Degrees Intervals

Dissociation Constants of Acetic Acid in 15 w/w % 2-Propanol/Water solvent from 5 to 35 oC at ten degrees intervals.

Emlyn Vélez1*, Damian Reyes1 and Carmen A. Vega2, PhD. 1Department of Chemical Engineering, University of Puerto Rico, Mayaguez, PR 00680 2Department of Chemistry, University of Puerto Rico, Mayaguez, PR 00680

Today is very important the solution where human organs are preserved for transplant purposes. A buffer solution of Acetic Acid and Sodium Acetate would be a preservative. However, this solution cannot contain only water as solvent, because this isn't sterile media. Alcohol/water mixtures have been recognized as potential candidates for such application. Then, it is important to know the dissociation constants of acids in alcohol/water solvents. Because an alcohol mixture, such as 2-propanol/water would alter the acid dissociation constant, it is necessary to obtain the Ka of acetic acid in 2-propanol/water, in which the pH equals pKa. The objective is to find the value of Ka for acetic acid in 2-propanol/water at different temperatures and proportions of the solvents mixture. Using electromotive forces (Emf) of a cell with hydrogen and silver/silver chloride electrodes and a multimeter the pKa of acetic acid is determined. The values of standard potential of the silver/silver chloride electrode in 2-propanol+water were required in order to determine the dissociation constants of acetic acid. Standard potentials for silver/silver chloride necessary for the calculations of this experiment were determined by extrapolation of experimental data from previous investigations at the working temperatures. The Emf of galvanic cells (without transfer), which contain acetic acid in Molal concentration from 0.01 to 0.1 as the electrolyte solution, were measured using a BX Precision 5492 5 ½ digit multi-meter. The silver/silver chloride electrodes were prepared in the laboratory using the thermal-electrolytic type of procedure. The hydrogen electrodes were prepared by electrode deposition of platinum in the two centimeters square platinum plate, using a 3.5 per cent (w/v) solution of Chloroplatinic Acid. The data were used to derive the standard changes of Gibbs energy, enthalpy, and entropy for the dissociation processes. Keywords: Dissociation Constants, Acetic Acid, hydrogen electrode

________________________________________ * To whom correspondence should be addressed. E-mail: cvega@uprm.edu