Amperometric and potentiometric titrations of copper and lead with ethylendiaminetetra acetate

Abstract

Amperometric titrations of copper (II) and lead (II) have been carried out with ethylenediaminetetraacetate in acetate buffer of pH 4.2 containing 0.01% gelatin, using the dropping mercury electrode as an indicator electrode. Titrations were made at-0.12 volt vs. S. C. E.. for copper (II), and at-0.60 volt vs. S. C. E.. for lead (II). Accurate results were obtained with both elements in the concentration range of 5×10-4 to 1×10-2 mol/l.Potentiometric titrations at constant current have also been applied to the determination of 5×10-4 to 1×10-2 mol/l. of copper (II) and lead (II) with the same titrants and supporting electrolyte and with the dropping mercury electrode as an indicator electrode. A saturated calomel electrode was used for the reference electrode. As was predicted from the theoretical considerations, potential jumps occurred before the equivalence points in all titrations. The observed deviations were compared with the theoretically calculated deviations. The concentrations of copper (II) and lead (II) initially present in the solution (C in mol/l) can be calculated with the same equation as given in a previ ouspaper, C=iα-ir/k V+v/V+cv/V, where c represents the concentration of titrants expressed in mol/l.; V, the initial volume of the solution titrated in ml.; v, the volume in ml.required before the indicator electrode reaches the given potential (-0.12 volt vs. S. C. E.. for copper (II) and-0.60 volt vs. S. C. E.. for lead (II)) ; iα, the applied constant current expressed in microamperes; ir, the residual current in microamperes at the given potential for the observed end point; and k, the sensitivity of the electrode expressed in microampere/mol/l. The results indicate that the potentiometric titration at constant current is applicable with reasonable accuracy to the determination of copper (II) and lead (II) in concentrations down to 5×10-4 mol/l.