R. A. Robinson

Solvation equilibria in very concentrated electrolyte solutions

A stepwise hydration-equilibrium model for aqueous electrolytes is developed and shown to give a good quantitative account of osmotic coefficients of strong, highly soluble electrolytes up to concentrations of 20–30 m. The main parameters needed are two equilibrium constants describing the stepwise hydration and the number of hydration sites. Choice of ion-size parameter has only a minor effect.

The system H2O−HCl−NH4Cl at 25°C: A study of Harned's rule

Electromotive-force measurements of cells containing hydrochloric acid and ammonium chloride at constant total molality have been used to determine the variation of the logarithm of the activity coefficient of hydrochloric acid with change in the amount of ammonium chloride in the solution. The results are interpreted in the light of the recent work of Pitzer, and it is found that Harneds rule holds for both electrolytes.

Thermodynamics of hydrobromic acid in water + 50 mass per cent methanol from e.m.f. measurements at 278.15 to 333.15 K

Electromotive-force measurements of cells of the type P t | H 2 ( g ) | H B r ( m ) i n H 2 O + M e O H | A g B r | A g at 12 temperatures from 278.15 to 333.15 K have been used to derive (a) the standard e.m.f. of the cell in water + 50 mass per cent methanol, (b) the activity coefficient of hydrobromic acid, (c) the relative partial molar enthalpy of HBr, and (d) the thermodynamic constants for the transfer of HBr from the standard state in water to the standard state in water + 50 mass per cent methanol. The molality m of the acid ranged from 0.0066 to 0.1 mol kg−1. The standard e.m.f. was determined by an extrapolation method making use of the extended terms of the Debye-Huckel theory.

Ionic product and enthalpy of ionization of water from electromotive force measurements

New e.m.f. data have been obtained for the cell: Pt, H2|MOH,NX|AgX|Ag at 25°C where M, N = Li, Na, K, Cs and X = Cl, Br, from which the ionic product (Kw) of water can be obtained (pKw= 14.004). Application of a theory of mixed electrolyte solutions to the results enables the variation of the apparent ionic product (K′w) with ionic strength and cation to be expressed in terms of the properties of the pure alkali metal halide and hydroxide solutions at the same total ionic strength. The conditions M = Li, N = K, X = Cl were selected for a study over the temperature range 0–60°C and from these measurements the enthalpy of ionization of water was calculated (ΔH°= 13430 ± 5 cal mol–1). The use of mixed cations in the cell minimises the variation of apparent ionic product with ionic strength, thereby reducing the uncertainty in the extrapolation to zero ionic strength felt previously to be the principal contributing factor leading to the discrepancy between calorimetric and e.m.f. derived values for the ionization enthalpy of water.

Solute-solvent effects in the acidic dissociation of the ampholyte N-tris(hydroxymethyl)methylglycine (“tricine”) in 50 mass % methanol-water solvent

The pK values for the two acidic dissociation steps of the ampholyte N-tris-(hydroxymethyl)methylglycine (“tricine”) in 50 mass % methanol-water solvent have been determined by emf measurements of cells of the type Pt|H2(g, 1 atm), tricine buffer, Br−, AgBr|Ag over the range 5 to 50°C (pK1)and 5 to 60°C (pK2).The standard thermodynamic quantities ΔHo, ΔSo, and ΔCpo for the two dissociation processes have been derived and are compared with the corresponding values for tricine and the parent glycine in water and with those for other acids in 50 mass % methanol-water solvent. Both tricine and protonated tricine become weaker acids when methanol is added to the aqueous solvent. It appears that a strong stabilization of the zwitterion in water is responsible for this behavior. This conclusion is supported by comparing the changes in entropy and heat capacity for the dissociation of tricine with the values of these quantities for the dissociation of “model” acids of simple structure, such as ammonium ion and acetic acid.

Osmotic coefficients of aqueous sodium carbonate solutions at 25°C

Isopiestic vapor pressure measurements are reported for aqueous sodium carbonate solutions at 25°C using sodium chloride as reference electrolyte. Osmotic and activity coefficients are calculated from the concentrations of the solutions in isopiestic equilibrium. The results are used to calculate the trace activity coefficients of carbonate ion in sodium chloride solutions; these should approximate the trace activity coefficient of carbonate ion in seawater. The solubility of sodium carbonate in water at 25°C has been determined.

Isopiestic measurements on aqueous mixtures of sodium chloride and strontium chloride

Isopiestic measurements have been made on NaCl−SrCl2 mixtures at 25°C over the ionic strength range 0.6–6 mole-kg−1. The results are interpreted in terms of current mixed-electrolyte treatments. The mixing behavior in this system is comparatively simple, but the Pitzer treatment is still clearly superior to the other treatments.

Activity coefficient of hydrochloric acid in aqueous solutions of sodium chloride

AbstractElectromotive-force measurements of the cell

Conductance of tetraalkylammonium salts in propylene carbonate at 25C

Pt;H_2 \left( {g,1{\text{ }}atm} \right)|HCl\left( {{\text{m}}_A } \right),NaCl\left( {{\text{m}}_B } \right)|AgCl;Ag