An aqueous solution contains 0 . 10 M H 2 S and 0 . 20 M HCl . If the equilibrium constant for the formation of HS - from H 2 S is 1.0 × 10 - 7 and that of S 2 - from HS - ions is 1.2 × 10 - 13 , then, the concentration of S 2 - ions in the aqueous solution is:

Step-by-step solution

HCl → H + + Cl - 0 . 2 + x + y 0 . 2 H 2 S ⇌ H + + HS - 0 . 1 - x 0 . 2 + x + y x - y ;   K a 1 = 10 - 7 HS - → H + + S 2 - x - y 0 . 2 + x + y y ;   K a 2 = 1 . 2 × 10 - 13 H + = 0 . 2 + x + y M = 0 . 2 M K a 1 = H + HS - H 2 S = 0 . 2 × HS - 0 . 1 - x = 0 . 2 HS - 0 . 1 ( x = negligible) HS - = K a 1 × 0 . 1 0 . 2 = 1 2 × 10 - 7 K a 2 = H + S 2 - HS - = 0 . 2   M S 2 - 1 2 × 10 - 7 S 2 - = K a 2 × 1 2 × 10 - 7 0 . 2 = 1 . 2 × 10 - 13 ×