Date of Award
Master of Science (MS)
David W. Ebdon
Stoichiometric association constants of NaSO4-, NaCO3- and NaHCO3- ion-pairs were determined over the temperature range 10 - 40°C at several ionic strengths by using a sodium ion selective electrode. At zero ionic strength values for K°A,NaSO4- are 15.8 ± .4, 8.5 ± .2 and 4.6 ± .3 at 10°, 25° and 40°C, respectively; like values for K°A,NaCO3- are 17.1 ± 1.4, 19.1 ± .6 and 21.0 ± .7. Values for K°A,NaHCO3° are 3.35 ± .07 and 6.75 ± .02 at 25°C and 40°C, respectively.
The apparent association constants for NaSO4- and NaCO3- can be reproduced by the equation log K'A = log K°A - 4AI½ + BI , where A is the Debye-Hückel limiting slope (equal to .51 in water at 25°C), B is an empirical constant and K°A is the thermodynamic association constant. The values of log K°A,NaSO4- are 1.20, .93 and .67 at 10°, 25° and 40°C, respectively; like values for log K°A,NaCO3- are 1.233, 1.281 and 1.323. Values of B for NaSO4- are 1.04, 1.67 and 2.30 at 10°, 25° and 40°C, respectively; like values for NaCO3- are .69, 1.13 and 1.58. The factor 4A equals 2.00, 2.04 and 2.10 at 10°, 25° and 40°C respectively. The apparent association constants for NaHCO3° can be reproduced by the general equation log K'A = log KcA - 2AI½ + BI . At 25° and 40°C, the values of log K°A,NaHCO3° are .525 and .826 and the values of B are .290 and .123, respectively.
A linear correlation between ΔH' (the enthalpy of formation of the ion pair from the free ions) and the ionic strength of the solutions has been obtained for each of the salts studied. The results show that as the ionic strength increases, ΔH' for sodium sulfate ion association changes from negative to positive, for sodium carbonate changes from positive to more positive and for sodium bicarbonate changes from higher to lower positive values. These correlations can be used to calculate the apparent association constants at various temperatures and ionic strengths.
Chung, Yan-chun, "Thermodynamics of Ion Association in Aqueous Solutions of Sodium Sulfate, Sodium Carbonate and Sodium Bicarbonate" (1978). Masters Theses. 3208.
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