REFERENCE SECTION: REDOX POTENTIALS Chemistry texts are often peppered with statements of the following type: 'potassium is a strong reducing agent'; 'calcium is a stronger reducing agent than magnesium'; 'acidified potassium manganate is a strong oxidizing agent'; and, 'fluorine is a stronger oxidizing agent than chlorine'. The quantitative basis for these and other related descriptions is the (continually expanding) set of physical quantities known as reduction potentials; a critical compilation of these data is: A. J. Bard et al., Standard Potentials in Aqueous Solution, Marcel Dekker, New York, 1985. Numerical values of redox potentials are rarely used in introductory courses, partly because their correct use is quite complicated: nevertheless, a selected sub-set of values - as shown in this first Table - does provide a useful point of reference. [Reductant and reducing agent are synonymous, as are oxidant and oxidizing agent.]
# These data have been obtained, under standardized conditions, using sophisticated electrochemical cells. The diagram shows the basic design of such cells; Cell 1 would be suitable for impoverished mortals, but the well-endowed (or alchemists) would surely prefer Cell 2.
Chemically, a metallic element (M) is characterized by its tendency to lose one or more electrons and form a positive ion; i.e., it is readily oxidized (Olé!): M ® Mn+ + ne-. One of several different methods of quantitatively comparing metallic character involves using oxidation potentials. In principle, these values can be determined by measuring potential differences of simple electrochemical cells. However, because published sources of reduction potentials contain data obtained under standardized conditions, it is both convenient and self-consistent to derive oxidation potentials from such sources. This derivation involved changing the sign of each value, assigning an arbitrary value of 0.00 V to a gold reference electrode, and then executing simple arithmetic.
Complete the Table below, which refers to data obtained under standard conditions (pH = 0; 298 K), by inserting the group number and period of each element and by indicating each transition metal with an asterisk.
Dr. R. Peters Contents' List
Selected Principles - Introduction (1)