The Thermal Temperature Coefficient of the Calomel Electrode Potential Between 0° and 70°C

Abstract

The moving (transported) ionic properties S and C are partial molal properties of the ion itself and include the effect of its electrical charge on that portion of the solvation layer which travels with the ion (Eastman first and second regions). The negatives of the ionic transport properties --S* and --C* measure the influence of the ion (plus its tightly bound waters if any) on the remainder of the solvent (Eastman third region). A positive value of S* identifies the ion as a structure maker in the third region. The sums X ----X -}-(--X*), where X ----S or C, measure the partial molal properties of the stationary ion, including the effect of the ionic charge on both Eastman second and third regions of the solvent. Observed values of C suggest a twofold effect of the ionic charge on its entourage of water molecules: a loosening of the O-H covalent bonds coupled with a stiffening of the O . . . H hydrogen bonds. The moving entropy and heat capacity of hydronium ion can be understood in terms of the hydrogen-bonded model of water structure, in which every H20 or I-I30 + can be 4-, 3-, 2-, 1-bonded to its neighbors or unbonded. By ascribing both bond and vibrational energy levels on this model, an approximate partition function is constructed for H20 and H30 +, which can be made to fit our data for the unitary entropy and heat capacity of H.~O + at 25 ~ and standard data for the entropy and heat capacity of H20 between 0 ~ and 100 ~ This model predicts the following fraction of hydrogen bonds broken in liquid H20 at 0 ~ 25 ~ , and 100~ 0.183, 0.218, and 0.310; in H30 + at 25 ~ , 0.094. The addition of H + to I-I~O thus introduces a distinct amount of structure to the H30 + .... (H20)4 complex since it reduces the number of hydrogen bonds broken at 25 ~ to a level, 9.4%, equal to half the number of hydrogen bonds broken in the liquid H20 .... (H20)4 complex at the melting point. The need to break about 12% more hydrogen bonds when the proton moves away at 25 ~ is consistent with a calculated heat of transport of 3530 cal/mol, which compares favorably with the observed heat of transport of around 3000 cal/mole (on the Agar postulate). The single-ion stationary heat capacities C for K +, Na +, Li +, and C1-obtained experimentally in the present study via the KCl-bridge postulate compare very favorably with theoretically calculated values of C, for these ions based on the statistical model of Scheraga-Griffith.A summary of the results of Part II (la) is provided in Table I where the standard moving (transported) entropy S ~ of chloride ion, and related quan-* Electrochemical Society Active Member. Key words: electrolytes, entropy of transport, heat capacity of transport, ionic entropy, ionic heat capacity, ions, partition function of water, partition function of hydronium ion, statistical mechanics, thermodynamic properties of salines, transported entropy, transported heat capacity. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.24...

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