Thermodynamic quantities of surface formation of aqueous electrolyte solutions X. Aqueous solution of 2:1 valence-type salts

Surface tension increments of 2:1 valence-type salts were studied in comparison with those of other type. [Display omitted] ► An aqueous solution of 2:1 valence-type salts show larger increments in surface tension than 1:1 type salts. ► The surface tensions of solutions of calcium salts were found to increase in the order CaCl 2 > CaBr 2 > CaI 2. ► Cations of 2:1 type salts have a less pronounced effect on surface tension than the halide anions. The behaviors of a series of calcium halides and of alkali earth metal chlorides in the air/water surface region were studied in comparison with those of alkali metal halides by measuring the surface tension increments of solutions. The effect of salts with divalent cations on the surface tension increments is more pronounced than that of uni-univalent salts, but there are some similarities between these two types. It seems that the anions cause a marked effect on surface tension which is proportional to the magnitude of hydration in the bulk water. We also observed a decrease in the entropy change of surface formation with increasing concentration. The importance of an electrical double layer at the surface is discussed in relation to these surface tension increments.