A solution contains 0.1M H_2S and 0.3M HCI. If K_a and K_(a2) for H_2 S are 1 xx 10^(-7) and 1.3 xx 10^(-13) respectively, calculate concentration of HS^- and S^- in the mixture.

A solution contains 0.1M H_2S and 0.3M HCI. If K_a and K_(a2) for H_2

1.	A solution contains 0.1M H_2S and 0.3M HCI. If K_a and K_(a2) for H_2 S are 1 xx 10^(-7) and 1.3 xx 10^(-13) respectively, calculate concentration of HS^- and S^- in the mixture.
Answer» SOLUTION :First ionisation, step 1 `,H_2 ShArr H^(+) +HS^(-) """ K_a = 1 xx 10^(-7)` Second ionisation, step 2,`HS^(-)hArr H^(+)+s^(2-) "" K_(a_2) = 3 xx 10^(-13)` Presence of HCI supresses the dissociation of `H_2 S` due to common ion effect of `H^(+)`. For step `1,1 xx 10^(-7)= ([H^+][HS^(-)])/( [H_2 S])=(0.3[HS^(-)])/( 0.1)` Cocentrationof `HS^(-) `,`[HS^(-)])= 3.3 xx 10^(-8)mol L^(-1)` or step` 2,1,.3 xx 10^(-13) = ([H^+] [S^(2-)])/([HS^(-)]) = ( 0.3 [S^(2-)])/(3.3 xx 10^(-8))` concentrationof `s^(2-) , [S^(2-)] = 1.43 xx 10^(-20) mol L^(-1)`