R. Roy, L. N. Roy, Ashley N. Simon
Apr 1, 2004
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Journal
Journal of Solution Chemistry
Abstract
N-tris[Hydroxymethyl]-4-aminobutanesulfonic acid (TABS) has been investigated for the determination of the values of the second dissociation constant, pK2, in water at 12 temperatures in the range 5–55°C, including 37°C. This zwitterionic compound is useful as a secondary pH standard in the range of pH (7–9) for physiological applications. The electromotive force (emf) measurements have been carried out using a hydrogen gas electrode and a silver–silver chloride electrode. The values of pK2 are fitted as a function of temperature with the following results: pK2 = 1671.305/T+14.8737−2.04383 ln T, where T is the thermodynamic temperature in Kelvins. The experimental values of pK2 are 8.834 ± 0.0005 and 8.539 ± 0.0004 at 25 and 37°C, respectively. The related thermodynamic quantities, Δ G°, Δ H°, Δ S°, and Δ Cp° characterizing the dissociation process have been derived from the pK2 and its temperature coefficients.