Limiting activity coefficient measurement technique

Dohnal, V., Hovorka, S. (1999) Exponential saturator A novel gas-liquid partitioning technique for measurement of large limiting activity coefficients. Ind. Eng. Chem. Res. 38, 2036-2043. 

Limiting activity coefficient data fcr a few water solvent systems measured by various researches using the techniques discussed are shown in Table II. The y ... 

The standard emf E° of the cell was determined by means of an extrapolation technique involving a function of the measured emf E (which was measured experimentally), taken to the limit of zero ionic strength /. A linear function of I was observed when the Debye-Hiickel equation (in its extended form) (12) was introduced for the activity coefficient of hydrobromic acid over the experimental range of molalities m. With this type of mathematical treatment, the adjustable parameter became a0, the ion-size parameter, and a slope factor / . This procedure is essentially the same as that used in our earlier determinations (7,10) although no corrections of E° for ion association were taken into account (e = 49.5 at 298.15°K). 

The use of cryoscopic measurements for the determination of activity coefficients in aprotic solvents has been very limited, although much information is available on the evaluation of molecular weights and studies of solvent association. Relative to protic solvents more information is available and the investigations of Gillespie and coworkers in sulphuric acid and related compounds have been compiled to indicate the general scope of this technique in protic solvents. The information is presented in alphabetical order by solvent. 

Analysis for traces of substances that act as catalysts for reactions can be both highly specific and sensitive. Calculations of the type carried out by Yatsimirskii indicate that, if the rate of a catalytic reaction can be measured spectrophoto-metrically with a change in concentration equivalent to 10 moles/1, and if the catalytic coefficient amounts to 10 cycles/min, the minimum concentration of catalyst that can be measured by following the reaction for 1 min is about 10 moles/1. Such sensitivities can be attained by few other analytical techniques. Tolg considers only mass spectroscopy, electron-probe microanalysis, and neutron-activation analysis methods applied to favorable cases to have better limits of detection than catalytic methods. 

Kineticists have been excited by the prospect of obtaining detailed information on the dynamics of chemical reactions at molecular level from molecular beam studies. The experimental difficulties of the technique are formidable and the results have been limited mainly to the reactions of alkali metal atoms. Molecular beam studies of transfer reactions are omitted here, where the emphasis is on bulk kinetics and the measurements of rate coefficients and Arrhenius parameters (activation energies and A-factors). 

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