Extraction of chloro complexes and radioisotope:

Give suitable explanation for the following:

i) Al (NO₃)₃  is a better salting out agent than NH₄NO₃  as for the enhancement in extraction is concerned but the latter is generally preferred over the former in different extraction systems.

ii) In making log- log plots of [Extractant] vs distribution ratio, the use of metal ion solutions of a carrier free radioisotope is generally recommended.

iii) In the extraction of chloro complexes of Zn (II), Cd (II) and Hg (II) by high molecular weight amines, in most of the cases, the extent of extraction follows the order Zn < Cd < Hg.

Answer:

i) NH₄NO₃  is preferred over Al (NO₃)₃  because it is easier to destroy NH₄NO₃  for   subsequent processing of the aqueous phase.

ii) In the log - log plots, it should be the equilibrium concentration of the extractant in the organic phase. It is difficult to find the unbound concentration of the extractant. The problem is partly resolved if extremely low concentration of the metal ion is used. Thus, the equilibrium concentration of the extractant can be taken the same as its initial concentration. In the labeled metal ion solution with no additional carrier, the concentration is very low and there is no difficulty in the quantification of the distribution of the metal in the two phases.

iii) The observed order in extraction follows the sequence of the formation constants of chloro complexes in the aqueous phase. It is the anionic chloro complexes which are getting extracted in the solution of high molecular weight amines.