Refer to the Integrative Example. Assume that the disproportionation of S₂O₃^2– is no longer spontaneous when the partial pressure of SO₂(g) above a solution with [S₂O₃^2–] = 1 M has dropped to 1 x 10^–6 atm. Show that this condition is reached while the solution is still acidic.

Integrative Example

For use in analytical chemistry, sodium thiosulfate solutions must be carefully prepared. In particular, the solutions must be kept from becoming acidic. In strongly acidic solutions, thiosulfate ion disproportionates into SO₂(g) and S₈(s).

Show that the disproportionation of S₂O₃^2–(aq) is spontaneous for standard-state conditions in acidic solution, but not in basic solution.