JOURNAL OF
CHEMICAL EDUCATION
AN OXIDATION-REDUCTION SCALE EDWIN S. HODGE Davidson College, Davidson. North Carolina
THE CONCEPTION of oxidation and reduction as applied to the change in valence states is diicult for some students in both the beginning and analytical chemistry courses to grasp. The writer has found the
Is-SCALE SHOWING STATES 08 THE IMPORTANT E L E ~ N T S
OXIDAT~ON-REDUCTION TION OP
OXIDA-
accompanying chart a help in explaining this fundamental principle of inorganic chemistry. A few of the more important elements having several valences have been shown on the chart. An element in
its free state with a zero charge is placed on the zero lme. At other proper points the element is noted with the number of charges which it cames in its most common compounds. We have quite a few elements with four or five states when the zero state is included, and certainly this state should be counted. The table is by no means complete or exhaustive, but is only given here as a suggestion of one method of approach in teaching this prinaple. Any movement upward on the scale, regardless of what the change may he, is oxidation. Likewise any movement downward, regardless of the position, is called reduction. Take, for example, the element sulfur. In its free state it has zero valence, while in the compound HnS it has the valence of minus 2. The reaction of Has with KMnO, will give precipitated sulfur in the free state, hence oxidation is the result. If free sulfur is treated again, by burning, for instance, Son will be the product, and we have further oxidation, the sulfur acquiring a valence of plus 4. If on further treatment SO8 is formed from Son, the valence of sulfur becomes plus 6. In many cases the changes here indicated are well-known reactions either in the laboratory or in industrial processes. Other elements could have been used, but those listed were taken as perhaps the most representative of each group.
