A.C. polarographic study of d.c. polarographic non-additive diffusion current phenomena and underlying fast homogeneous redox reactions
✍ Scribed by H. Yamaoka
- Book ID
- 104149009
- Publisher
- Elsevier Science
- Year
- 1972
- Weight
- 556 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0022-0728
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✦ Synopsis
When two (or more) reducible species are present, the total d.c. polarographic limiting diffusion current is not always equal to the sum of the limiting diffusion currents of the individual species (the so-called "non-additive", "concealed" or "latent" diffusion current phenomena) ~ 4. It has been postulated that the non-additivity of diffusion currents can occur as a result of a very fast homogeneous redox reaction in the diffusion layer between one reducible species and the product resulting from the reduction of another, when the species have significantly different diffusion coefficients 4. For the majority of polarographically reducible species and their reduction products, however, the magnitude of diffusion coefficients is of the same order under comparable working conditions (see e.9. ref. 1, p. 144). Hence the non-additivity phenomena are usually more or less overshadowed by experimental errors inherent in the conventional d.c. polarographic technique.
A.c. polarographic technique has recently been recognized by the present author as a method free from the shortcomings of d.c. technique for the study of nonadditivity phenomena and the underlying fast homogeneous redox reactions responsible for them. In the following this will be demonstrated for a limited number of cases. Redox couples whose kinetic data in homogeneous media are available have been used as pilot ions. 2. EXPERIMENTAL 2.1. Reagents C0(NH3)63, Co(NH3)5H203 and Co(NH3)sC1 2 were prepared by recrystallization of commercial salts (in chloride form ; Hopkin and Williams) from aqueous HCI04 solution. [Co(NH3)5F ] (C104)2 was prepared by a standard procedure 5. The blue stock solution of VO(CIO4)z was prepared from NH4VO 3 (B.D.H.) by reducing with S02 gas (I.C.I.) and boiling out the excess 6. Eu-(C104)3 was prepared by dissolving Eu203 (Fluka) in aqueous HCI04 solution. Commercial [Cr(H 20)6 ] (C104)3 (K.E.K.), anhydrous Fe(Cl04)3 (Alfa), Ka[Fe(CN)6 ] (Merck), Pb(ClO4)z (Alfa), NaCl04 (Fluka) and HCI04 (RdH) were used. All chemicals used were of analytical grade and were not further purified. Doubly-distilled water was used throughout.