An aqueous solution of a metal bromide M B r 2 0 . 05 M is saturated with H 2 S . What is the minimum pH at which MS will precipitate? K s p for M S = 6 . 0 × 10 - 21 . Concentration of saturated H 2 S = 0 . 1 M ; K 1 = 10 - 7 and K 2 = 1 . 3 × 10 - 13 for H 2 S . [Report your answer by rounding it upto nearset whole number]

Step-by-step solution

For the precipitation of MS form a solution of M B r 2 by passing H 2 S K sp MS = M 2 + S 2 − or 6 × 10 - 21 = 0 . 05 S 2 - or S 2 - = 1 . 2 × 10 - 19 M i.e. precipitation of MS will start when H 2 S provides 1 . 2 × 10 - 19 M ion of S 2 - For H 2 S ⇌ 2 H + + S 2 − K = K 1 × K 2 = [ H + ] 2 [ S 2 - ] [ H 2 S ] or 10 - 7 × 1 . 3 × 10 - 13 = [ H + ] 2 [ 1 . 2 × 10 - 19 ] 0 . 1 or H + = 1 . 04 × 10 - 1 ∴ pH=0.9826