Stability of the magnesium bicarbonate ion pair from 10 to 90/sup 0/C

Journal Article · Wed Jun 01 04:00:00 EDT 1977 · Am. J. Sci.; (United States)

DOI:https://doi.org/10.2475/ajs.277.6.697· OSTI ID:7085408

Siebert, R M ^[1]; Hostetler, P B

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1. Univ. of Missouri, Columbia

The dissociation constants of the aqueous MgHCO/sub 3//sup +/ ion pair were determined experimentally from 10 to 90/sup 0/C at 15/sup 0/ intervals. The experimental pH change between alternating additions of MgCl/sub 2/ and KHCO/sub 3/ to MgCl/sub 2/--KHCO/sub 3/ solutions in equilibrium with CO/sub 2/ was used to calculate the dissociation constants by a new floating point method which does not require absolute pH and P/sub CO/sub 2// values. The approach reduces the sources of error to single-ion activity coefficients and reference electrode liquid-junction potentials. The experimental pK/sub MgHCO/sub 3//sup +// (-log K/sub dissociation/) at 25/sup 0/C is 1.07 +- 0.03, and the pK's increase smoothly to 1.34 +- 0.03 at 90/sup 0/C. The 25/sup 0/C result is in general agreement with several previous determinations; the pK variation as a function of temperature is in excellent agreement with that predicted by the Fuoss electrostatic ion pair theory. Derived values of ..delta..G/sub R//sup 0/, ..delta..H/sub R//sup 0/, and ..delta..S/sub R//sup 0/ of dissociation at 25/sup 0/C are 6087.7 +- 167 J mol/sup -1/ (1455 +- 40 cal mol/sup -1/), -4987.3 J mol/sup -1/ (-1192 cal mol/sup -1/), and -37.15 J deg/sup -1/ mol/sup -1/ (-8.88 cal deg/sup -1/ mol/sup -1/), respectively.

• OSTI ID: 7085408
• Journal Information: Am. J. Sci.; (United States), Journal Name: Am. J. Sci.; (United States) Vol. 277:6; ISSN AJSCA
• Country of Publication: United States
• Language: English

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ADDITIVES
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
AQUEOUS SOLUTIONS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CATIONS
CHALCOGENIDES
CHARGED PARTICLES
CHEMICAL REACTION KINETICS
CHLORIDES
CHLORINE COMPOUNDS
DISPERSIONS
DISSOCIATION
HALIDES
HALOGEN COMPOUNDS
IONS
KINETICS
MAGNESIUM CHLORIDES
MAGNESIUM COMPOUNDS
MIXTURES
OXIDES
OXYGEN COMPOUNDS
PH VALUE
POTASSIUM COMPOUNDS
REACTION KINETICS
SOLUTIONS
STABILITY
TEMPERATURE DEPENDENCE