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The first thermodynamic dissociation constants of boric acid in aqueous solution of lithium chloride with borate at five different temperatures from 278.15 to 318.15 K were evaluated from ernf values of the cell without liquid junction potential with the improved extrapolation and polynomial approximation on the basis of Pitzer's theory. Values obtained from both methods are in good agreement with each other. Pitzer's parameters β(0) and β(1) of LiB(OH)4 and other thermodynamic quantities of dissociation process of boric acid are obtained. Results have been discussed.

Values of e.m.f. for the cell without liquid junction: Pt H 2 ( p = 101.325kPa)|K 2 B 4 0 7 ( m 1 ) LiCl( m 2 )|AgCl Ag are reported at seven constant ionic strengths from 0.07 to 2.0 mol·kg −1 at five temperatures from 278.15 K to 318.15 K. The standard association constant K a of the ionic pair Li + B(OH) 4 − , is determined by a fit with the cell results. The dependence of p K a on temperature T is expressed by the empirical equation: p K a = −149.8(K/ T ) + 0.09024 − 2.112·10 −3 ( T /K). The other thermodynamic quantities of the association process were also calculated and show that the driving force for the ion association reaction is the association entropy.