Figure 4.1
The effect of pH and complex formation on extracting species.
(a) log 10 D against pH for the extraction of benzoic acid, Ka = 6.3 × 10 –^5 mol dm–^3.^
(b) log 10 D against log 10 ([I–]/mol dm–^3 ) for the extraction of I 2.The partition coefficient is given by
and the distribution ratio by
Substituting for in (4.14) and rearranging,
Thus, the presence of iodide affects D in such a way that at very low concentrations and iodine
is extracted with greatest efficiency. At high iodide concentrations, Kf[I–]aq >> 1, and D is reduced with
a consequent reduction in the extraction of iodine (Figure 4.1(b)).
Effect of Association
The distribution ratio is increased if association occurs in the organic phase. Carboxylic acids form
dimers in solvents of low polarity such as benzene and carbon tetrachloride,