A study on the estimation of activity coefficient of tris(1, 10-phenanthroline)Fe(II) iodide in aqueous phase by means of solvent extraction with nitrobenzene

The extraction of tris(1, 10-phenanthroline)Fe(II) iodide into nitrobenzene was investigated at a constant concentration (6·06 × 10−5 mol/l) of the chelate salt, the ionic strength of the aqueous phase being varied up to about 0·3 by adding a second salt, such as sodium acetate or sodium sulfate, both of which are not extracted within the experimental error. From the changes of the distribution ratio with the ionic strength, the activity coefficients of the chelate salt in the range of above ionic strength were obtained. The best fit equation for the representation of the mean activity coefficients was estimated to be −logf± = A|z1z2| √ (I)[1 + 8·2B√ (I)] −0·06I, in which the closest distance of approach of free ions seemed to be reasonable for the bulky chelate salt.