Scientia Sinica

STUDIES ON THE ACTIVITY COEFFICIENTS OF NONELECTROLYTES IN AQUEOUS SALT SOLUTIONS*

I. THE EFFECT OF COBALT-AMMINES ON THE SOLUBILITIES OF n-VALERIC ACID IN WATER** -

Tzu-Cutnc Huane (#¢5-§81) and Wen-Cuen YAne (#53¢78 )

(Department of Chemistry, Peking University)

INTRODUCTION

If salt is added to a saturated aqueous solution of nonelectrolyte, its solubility will change. Such phenonmenon is called salting-out or salting-in depending upon the increase or decrease of solubility of the nonelectrolyte. Although salting-out is most common, salting-in is occasionally found. Either of these effects is called salt effect in this paper.

In 1889, Setschenow™ showed that the salt effect can be generalized by the following empirical equation,

log = = RkC,, (1)

where Sy is the solubility of nonelectrolyte in pure water, S is that in aqueous salt solution and C, is the concentration of salt. k is called the “salting-out constant”. For k>0, S<Sp, ie., salting-out; for R<0, S>So, ie., salting-in. Eq. (1) holds from dilute to concentrated solution of salt, (several mols per litre). According to thermodynamics, Sp /S=f, where f is the activity coefficient of nonelectrolyte. Thus Eq. (1) can be written as

log f= RC, . (2)

If a weak base or a weak acid is used in substitution for the nonelectrolyte, Eq. (2) is still approximately correct.

*First published in Chinese in Acta Chimica Sinica, Vol. XXII, No. 1, pp. 67—77, 1956.

**Part of a thesis submitted by W. C. Yang to the Faculty of Graduate School of Chemistry, Peking University, September 1954.

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