ABSTRACT
The electronic structure of the atoms of sulfur, selenium, tellurium, and polonium is close to that of the inert gases following them in the periodic chart. The standard potentials of sulfur were for the most part calculated thermodynamically rather than found in direct experiments. Many redox systems of sulfur are irreversible. Since sulfur dissolves in excessive sulfide to form polysulfides, it has proved impossible to measure the standard potential of this system experimentally. Thus in 1 M solution sulfuric acid is a poor oxidant which is far weaker than sulfurous acid. However, concentrated sulfuric acid, especially when heated, is a stronger oxidant than sulfurous acid. A more detailed consideration of redox properties of the sulfate-sulfite couple must evidently allow also for the changes in the properties of second redox system, which interacts with the sulfate-sulfite system when one passes from standard conditions to the solutions in concentrated sulfuric acid.
