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Explanation and Exercise Guide


In the extraction of an inorganic substance by an organic solvent the former must be present in a chemical form that is soluble in water and the organic solvent used. Extraction systems for metal ions are generally based on the formation of coordinated complexes or ion association complexes. Complexes can be formed with simple ligands as shown below (taken from ‘Solvent Extraction in Analytical Chemistry’ Morrison & Freiser).

NH3 > RNH2 > R2NH > R3N

H2O > ROH > R2O > R2CO3 > RCHO

R3 > R3P > R2S

Where R = alkyl or aryl group

The relative strengths of the complexes formed with simple ligands approximately correlates with the relative strengths of the ligands as Lewis bases. The formation of a complex with simple ligands does not necessarily confer solubility in an organic solvent. The solubility must be conferred by the formation of a soluble association complex with the organic solvent used. Chelate compounds formed with polyfunctional ligands such as dimethyl glyoxime are often used for solvent extraction. Heteropoly acids such as silicomolybdic can also be used. In some cases the covalent nature of the substance itself may allow extraction into a non-polar solvent (i.e. the halogens).

The % of substance extracted and the distribution ratio (D) are related by the equation:

\% \, extracted\,=\frac{100\cdot D}{D+\left(\frac{V_{aq}}{V_{org}}\right)}

The value of D in any system must be determined empirically for a variety of conditions. For a given system D will depend on:-

The PUREX process uses solvent extraction to separate uranium and plutonium. To show this principle at work, this experiment will extract phosphorous from an aqueous solution by converting it into phosphomolybdic acid and using ethyl acetate to extract it.

Experimental Procedure

Experimental procedure for the separation of radioisotopes by solvent extraction

Questions for the Students


How to do calculations or other important aspects for the theory that is not directly related to exercise.

Safety Aspects


Description of the equipment needed and used during the exercises.

Preparation for the lab Supervisor

The preparation that the lab Supervisor needs to do to ready the lab.

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