Question

Many of the communities around Oxford rely on wells for drinking water, and the aquifers this water comes from typically contain a large amount of iron sulfide. A common type of bacteria produces dissolved H₂S. H₂S is a weak acid, and the dissolved H₂S exists in equilibrium with HS^- and S^2-.

(a)If the total concentration of dissolved sulfur (

Answer 1

H2S + H2O -> HS^- + H3O⁺ Ka1 = [HS-] * [H3O+]₁ / [H2S]    [HS-] = [H3O] because it is produced in the same amount

HS- + H2O -> S2- + H3O+ Ka2 = [S2-] * [H3O+]₂ / [HS-]     [S2-] = [H3O+]

Ka1+ Ka2 = [S2-] * [H3O+]² / [H2S] = [H3O+]³ /[H2S]

[H2S] = [H3O+]³ / (Ka1+Ka2)    [H3O+] = 10^-pH = 10^-7

[H2S] = (10^-7)³ / (1.1*10^-7 + 1.3*10^-13) = 9.1*10^-15

Ka1 = [HS-] * [H3O+]₁ / [H2S] ->because H3O is the same as HS- -> Ka1 = [HS-]² / [H2S]

[HS-] = = 3.2*10^-11

[sulfur] = 1*10^-5 = [H2S] +[HS-] + [S2-] -> [S2-] = 1*10^-5 -[H2S] - [HS] = 9.9*10^-6