# Frost diagram and acidic/basic conditions.

The Frost diagram for sulfur shows the relative stability (in terms of cell potentials) of the possible aqueous oxidation states. What is the reason for the instability of higher oxidation states in the acidic regime and their stability in the basic regime ? Something I have always noticed but never been able to apply chemical intuition to.

• Negative charges aren't happy in acidic media. – Dissenter Mar 24 '15 at 16:46
• Yes, but the Frost diagram shows us the difference between the S oxidation states; degree of protonation doesn't affect that. – J. LS Mar 24 '15 at 17:14

$$\ce{HS- + 4 H2O -> 8e- + 9H+ + SO4^{-2} }$$