IIT JEE , AIEEE Forum - Chemistry , Physical Chemistry

iitaspirant10

A solution contains 0.1M H₂S and 0.3 M HCl

Find concentration of S₂^- and HS^- ions

given, K_a1 and K_a2

iitaspirant10

ps reply

dev_22oct

dear your question is not complete. bt i knw that this is rorkee 1992 problem.

H₂S--------> H⁺ + HS^- K_a1= 10^-7

HS---------> H⁺ + S^2- K_a2 =1.3 x10^-13

HCl----> H⁺ + Cl^-

now due to common ion effect the dissociation of H₂S is suppressed and the [H⁺] in the solution is due to HCl

K_a1 = [H⁺][HS^-]

---------------

[H₂S]

10^-7 =[0.3][HS^-]/[0.1]

Therefore [HS^-]= 3.3 x10^-8 M

Ka₂ =[H⁺] [S^2-]/[HS^-]

K_a1 x K_a2=[H⁺]²[S²]/[H₂S]

Placing Ka1 and Ka2 in the obove expression we get [S^2-] as 1.4x10^-20 M