The Geysers Geothermal field in Sonoma County has soils containing cinnabar [HgS(s)] because it is an old mercury mining district. You measure roughly 10-7 atm of H2S(g) in soil gases and the pH of the soils is quite acid (pH=3.2) because of the production of sulfuric acid by sulfide-oxidizing bacteria.
a) What would the concentration (or activity) of Hg2+(aq) be in the solution if equilibrium existed between the water in soil pores, the gas and cinnabar?