Measurement of activity coefficients

Many different techniques can be used to measure activity coefficients of electrolytic solutes, many of which are electrochemical. Most of these methods are reviewed in standard references (e.g., Harned and Owen, 1958 Monk, 1961 Robinson and Stokes, 1968, Ch. 8). Solutions of geological interest can span considerable temperature ranges, and it has often proven simplest experimentally to measure the activity of the 

The theoretical method used in relating the water activity to solute activity in each of these methods is an interesting application of the Gibbs-Duhem equation introduced in Chapter 9 ( 9.2.6). There are several ways of doing this for further details see Liu and Lindsay (1972) and Wood et al. (1984). 

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Gruber, D., Langenheim, D., Gmehling, J. (1997) Measurement of activity coefficients at infinite dilution using gas-liquid chromatography. 6. Results for systems exhibiting gas-liquid interface adsorption with 1-octanol. J. Chem. Eng. Data 42, 882-885. 

Krummen, M., Wasserscheid, R, and Gmehling, J., Measurements of activity coefficients at infinite dilution in ionic liquids using the dilutor technique, /. Chem. Eng. Data, 47, 1411, 2002. 

The Measurement of Activity Coefficients in Concentrated Electrolyte Solutions 103... 

G,t can be obtained, in principle, from measurements of activity coefficients (equation 15) ... 

For lithium chloride there are also two sets of e.m.f. measurements of activity coefficient values. Precise measurements at 25, 30 and 35 C on the cell... 

STATIC MEASUREMENTS OF ACTIVITY COEFFICIENTS AND SURFACE TENSIONS OF SOME SYSTEMS AT VERY LOW MOLE FRACTION. 

Khoskbarchi M, Vera JH (1996) Measurements of activity coefficients of amino acids in aqueous electrolyte solutions experimental data for the system HjO-iNaCl-iglycine and HjO-i-NaCl-hDL-sdanine at 25 °C. Ind Eng Chem Res 35 2735 - 2742... 

Mutelet, F. and Jaubert, J.N. (2007) Measurement of activity coefficients at infinite dilution in l-hexadecyl-3-methylimidazolium tetrafluoroborate ionic liquid. J. Chem. Thermodyn., 39 (8), 1144-1150. 

FUW] Measurement of activity coefficient from passing CO-C02-Ar mixture over Fe-Nb melts 1560°C (hquid)... 

There are many methods which enable determination of activity coefficients in infinite dilution. They are mostly based on differential ebulliometry or on gas chromatographic measurement of retention time, subsequently retention volume. The headspace chromatographic analysis is another popular technique which enables measurement of equilibrium compositions at given temperature. Some similarity with static methods may be found, however, degassing is not required since the pressure is not measured. The data may be obtained rather quickly, nevertheless their accuracy is not very high. Methods for measurement of activity coefficients in infinitely diluted solutions are not described here in detail because such data are not included in this volume. 

The excess free energy may be readily calculated from experimental measurements of activity coefficients by use of equation (9 46)i It will be seen that expressing it as a power series is a means of giving empirical description to deviations from ideality which is alternative to the expressions for the individual activity coefficients discussed in 7 8. It is t Wilson, G. M., J. Am. Chem. Soc. 88 (1964), 127. 

In principle the activity coefficients yb of solute substances B in a solution can be directly determined from the results of measurements at ven temperature of the pressure and the compositions of the liquid (or solid) solution and of the coexisting gas phase. In practice, this method fails unless the solutes have volatilities comparable with that of the solvent. The method therefore usually fails for electrolyte solutions, for which measurements of ye in practice, much more important than for nonelectrolyte solutions. Three practical methods are available. If the osmotic coefficient of the solvent has been measured over a sufficient range of molalities, the activity coefficients /b can be calculated the method is outlined below under the sub-heading Solvent. The ratio yj/ys of the activity coefficients of a solute B in two solutions, each saturated with respect to solid B in the same solvent but with different molalities of other solutes, is equal to the ratio m lm of the molalities (solubilities expressed as molalities) of B in the saturated solutions. If a justifiable extrapolation to Ssms 0 can be made, then the separate ys s can be found. The method is especially useful when B is a sparingly soluble salt and the solubility is measured in the presence of varying molalities of other more soluble salts. Finally, the activity coefficient of an electrolyte can sometimes be obtained from e.m.f. measurements on galvanic cells. The measurement of activity coefficients and analysis of the results both for solutions of a single electrolyte and for solutions of two or more electrolytes will be dealt with in a subsequent volume. Unfortunately, few activity coefficients have been measured in the usually multi-solute solutions relevant to chemical reactions in solution. 

At this point, mention should be made of the reversed-flow gas chromatography technique, a version of IGC that has been applied successfully to the measurement of activity coefficients in polymer solutions [78], and also for determining Flory-Huggins interaction parameters and solubility parameters in polymer-solvent systems [79]. 

Agathonos, P. and Karaiskakis, G. (1988) Measurement of activity coefficients in polymer solutions by the reversed-flow technique. Chromatographia, 25, 453—454. 

LER1 Leroi, J.-C. Masson J.-C. Renon, H. Fabries, J.-F. Sannier, H. Accurate measurement of activity coefficients at infinite dilution by inert gas stripping and gas chromatography. Ind. Eng. Chem., Process Des. Dev. 16 (1977) 139-144. 

Mutelet, F. Jaubert, J.-N. Measurement of Activity Coefficients at Infinite Dilution in 1-... 

Krummen, M Wasserscheid, P. Gmehling, J. Measurement of Activity Coefficients at... 

Domanska, U. Laskowska, M. Measurements of Activity Coefficients at Infinite... 

Domanska, U. Paduszynski, K. (2010). Gas-liquid chromatography measurements of activity coefficients at infinite dilution of various organic solutes and water in tii-iso-butylmethylphosphonium tosylate ionic liquid.. Chem. Thermodyn., 6, 42, 707-711. 

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