An acidified solution of 0 . 05   M   Zn 2 + is saturated with 0 . 1   M   H 2 S . What is the minimum molar concentration ( M ) of H + required to prevent the precipitation of ZnS ? Use K sp ( ZnS ) = 1 . 25 × 10 - 22 and overall dissociation constant of H 2 S ,   K NET = K 1 K 2 = 1 × 10 - 21
A. A
For ZnS K sp ( ZnS ) = Zn 2 + × S 2 - = 1 . 25 × 10 - 22 = 0 . 05 × S 2 - = 1 . 25 × 10 - 22 S 2 - = 25 × 10 - 22 For H 2 S H 2 S 0 .1   M ⇌ 2 H + + S 2 − 25 × 10 − 22 K a = H ' S 2 - H 2 S = 1 × 10 - 21 = H + 2 × 25 × 10 - 22 0 . 1 = 1 × 10 - 21 H + 2 = 1 25 H + = 1 5 H + = 0 . 2   M
Related: Chemistry — Ionic Equilibrium · All PYQ Banks