Question
Chemistry Question on Equilibrium
An aqueous solution contains 0.10MH2S and 0.20MHCl . 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
Answer
3×10−20
Explanation
Solution
In presence of external H+,
H2S⇌2H++S2−,Ka1⋅Ka2=Keq
∴[H2S][H+]2[S2−]=1×10−7×1.2×10−13
[0.1][0.2]2[S2−]=1.2×10−20
[S2−]=3×10−20