Acidic dissociation constant and related thermodynamic quantities for monoethanolammonium ion in water from 0-degrees to 50-degrees-C

Abstract

TWf! nty-three butTer solu tions composed of approximately eCJual molal amounts of monoethanolamine (2-aminoethanol) and monoethanolammoniurn chloride ill water were studied by electromotive-force methods at 11 temperatures from 0° to 50° C. The values obtained for the acid ic dissociation constant, K bh , of the ethanolammonium ion are given in this range of temperatures by-log K bh = 2677.91 /T + 0.3869 + 0.0004277T, where T is the temperature on t he K elvin scale. The changes of free energy, heat content, entropy, and heat capacity that accompany the dissociation of 1 mole of ethanolamm.onium ion in the standard state were calculated from the dissociation constant and its tem perature coefficient. Dissociation of a mol e of ethanolammonium ion resu lts in a small decrease of h eat capacity. In this r espect ethanolammonium ion resembles ammonium ion rathe r than the methyl-substitu ted ammonium ions, for which rather large increases of heat capacity on di ssociation have been found.