Polarographic Study of Zn(II)- Thiocyanate System

Chemical Laboratories, Agra College, Agra

Manuscript received 26 March 1979, accepted 30 November 7979

Polarographic behaviour of Zn(II) in the presence of increasing [thiocyanate] has been studied at a constant ionic strength μ=2 (NaNO₂). The reduction has been found to be diffusion controlled and quasi-reversible E_1/2 of Zn(II) gets shifted to more negative potentials with increasing [thiocyanate] thereby showing complex formation. The reversible half-wave potential, (E^r_1/2) and the kinetic parameters of the electrode process have been evaluated by Gellings method. Zn(II) forms three successive complexes : [Zn(CNS)]⁺, [Zn(CNS)₂] and [Zn(CNS)₅]^- and not four as reported by earlier workers¹. Stability constants of the three complexes are ß₁ =3, ß₂, =4 and ß₃ =10. The percentage distribution of Zn(II) in its various forms as a function of ligand concentration has also been presented.