ISSN:
1572-8927
Keywords:
Acid dissociation constant
;
acid-base indicator
;
pressure-dependent spectrophotometric measurements
;
sodium borate ion pair
;
ion association
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract A high pressure UV-visible spectrophotometer was used to determine the dissociation constant of boric acid using an indicator technique. The measurements were made at 25°C and at ionic strengths of 0.1 and 1.0m over a pressure range of 1 to 2000 atm. Extrapolation to I=0 gave a thermodynamic dissociation constant of 5.16×10−10 at 1 atm. The pressure dependence yielded a partial molal volume change of −28.9 and −31.8 cm3-mol−1 and a compressibility change of −3.1 and −4.8×10−3 cm3-mol−1-atm−1 for the dissociation at I=0.1 and 1.0m, respectively. The association constant for the formation of the sodium borate ion pair was determined by comparing the acid constants in tetramethylammonium chloride to those in sodium chloride solutions. Extrapolation to I=0 yielded a KA for [NaB(OH)4] of 0.64 at 1 atm. The pressure dependence of KA gave $$\Delta \overline V ^o = 8.39 {\text{cm}}^{\text{3}} {\text{ - mol}}^{{\text{ - 1}}} $$ and $$\Delta \overline K ^o = 1.6 \times 10^{ - 3} {\text{cm}}^{\text{3}} {\text{ - mol}}^{{\text{ - 1}}} - atm^{ - 1} $$ for the formation of the ion pair.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00651003
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