Answer to Question #48517 in Inorganic Chemistry for Claire

Question

Please could you calculate the partial pressure of H2S at pH7, 105 bar pressure at 30 ppm S−2

My attempt so far:

H2S+H2O↽⇀H3O++HS−

HS−+H2O↽⇀H3O++S2−

With K1=9.1×10−8 and K2=1.3×10−18 respectively

pH=7 -> [H3O+]=10−7 and 30 ppm S2− -> [S2−]=9.36×10−4

I worked out the equilibrium equation and found that [HS−]=9.36×10−4, which when plugged into the first equation implies [H2S] is also 9.36×10−4 because of the very small values of K. Is this correct so far, or have I missed something? It’s been a long time since my chemistry classes!