Oxidation and Reduction in Solution

Galvanic CELLS axe electrochemical cells in which an external electric current is produced by an internal chemical reaction.1 7 As an example, consider first the dissolution of zinc metal in a strong aqueous acid to give Zn2+ (aq) and hydrogen gas  

The electrode in the half-cell in which oxidation is occurring is said to be the anode (here, the zinc metal), whereas the other is the cathode (here, the platinum). In principle, we could connect any pair of feasible half-cells to form a galvanic cell the identity of the half-cells will determine which electrode will act as the anode, and which the cathode. The electromotive force (EMF, in volts) of the cell will depend on the identity of the half cells, the temperature and pressure, the activities of the reacting species, and the current drawn. An EMF will also be generated by a cell in which the two half cells are the chemically identical except for a difference in reactant activities (concentrations) this is called a concentration cell. 

If we choose a set of standard conditions (cf. Section 2.3) and one convenient half-cell to serve as a reference for all others, then a set of standard half-cell EMFs or standard electrode potentials E° (Appendix D)1-9 can be measured while drawing a negligible electrical current, that is, with the cell working reversibly so that the equations of reversible thermodynamics 

By international agreement, the algebraic sign of E° for a half-cell is chosen to be the same as its electrical sign relative to the SHE. This means, in effect, that we must write the half-reactions with the electrons on the left-hand side in other words, E° values are taken to be reduction potentials. Consequently, a reagent such as chlorine that is more oxidizing than aqueous H+ (— H2) under standard conditions will have a positive E° 

Note that reducing reagents (i.e., suppliers of electrons) appear on the right in a half-reaction. 

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Heteropolyacids (HPA) are the unique class of inorganic complexes. They are widely used in different areas of science in biochemistry for the precipitation of albumens and alkaloids, in medicine as anticarcinogenic agents, in industry as catalysts. HPA are well known analytical reagents for determination of phosphoms, silica and arsenic, nitrogen-containing organic compounds, oxidants and reductants in solution etc. 

Refs. [i] Levich VG (1966) Present state of the theory of oxidation and reduction in solution (bulk and electrode reactions). In DelahayP (ed) Adv electrochem electrochem eng, vol. 4. Interscience, New York, pp 249-371 [ii] Kuznetsov AM, Ulstrup J (1999) Electron transfer in chemistry and biology. Wiley, Chichester [iii] Nazmutdinov RR, Glukhov DV, Tsir-lina GA, Petrii OA, Botukhova GN (2003) J Electroanal Chem 552 261... 

The following scheme of classification has been found to work well in practice it is not a rigid one since some of the anions belong to more than one of the subdivisions, and, furthermore, it has no theoretical basis. Essentially the processes employed may be divided into (A) those involving the identification by volatile products obtained on treatment with acids, and (B) those dependent upon reactions in solution. Class (A) is subdivided into (i) gases evolved with dilute hydrochloric acid or dilute sulphuric acid, and (ii) gases or vapours evolved with concentrated sulphuric acid. Class (B) is subdivided into (i) precipitation reactions, and (ii) oxidation and reduction in solution. 

Chapter 15 Oxidation and Reduction in Solution 15.2 Manipulation and Use of Electrode Potentials 15.2.1 Example Analysis of Brass... 

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