An aqueous solution contains 0.10 M H2S and 0.20 M HCl . If the equilibrium constants for the formation of HS- from H2S is 1.0 × 10-7 and that of S2- from HS- ions is 1.2 × 10-13 then the concentration of S2- ions in aqueous solution is -

Question

An aqueous solution contains 0.10 M H2S and 0.20 M HCl . If the equilibrium constants for the formation of HS- from H2S is 1.0 × 10-7 and that of S2- from HS- ions is 1.2 × 10-13 then the concentration of S2- ions in aqueous solution is - (A) 5 × 10-8 (B) 3 × 10-20 (C) 6 × 10-21 (D) 5 × 10-19

Tardigrade Admin · Accepted Answer

In presence of external H +, H 2 S leftharpoons 2 H ++ S 2-, K a 1 ⋅ K a 2= K eq ∴ ([ H +]2[ S 2-]/[ H 2 S ])=1 × 10-7 × 1.2 × 10-13 ([0.2]2[ S 2-]/[0.1])=1.2 × 10-20 [ S 2-]=3 × 10-20

$5 \times 1 0^{- 8}$

$3 \times 1 0^{- 20}$

$6 \times 1 0^{- 21}$

$5 \times 1 0^{- 19}$

Q. An aqueous solution contains 0.10MH2​S and 0.20MHCl . If the equilibrium constants for the formation of HS− from H2​S is 1.0×10−7 and that of S2− from HS− ions is 1.2×10−13 then the concentration of S2− ions in aqueous solution is -

5×10−8

3×10−20

6×10−21

5×10−19

In presence of external H+, H2​S⇌2H++S2−,Ka1​​⋅Ka2​​=Keq​ ∴[H2​S][H+]2[S2−]​=1×10−7×1.2×10−13 [0.1][0.2]2[S2−]​=1.2×10−20 [S2−]=3×10−20

$5 \times 1 0^{- 8}$

$3 \times 1 0^{- 20}$

$6 \times 1 0^{- 21}$

$5 \times 1 0^{- 19}$