Question

The first ionization constant of H₂S is 9.1 × 10 ^–8 . Calculate the concentration of HS^– ion in its 0.1 M solution. How will this concentration be affected if the solution is 0.1 M in HCl also? If the second dissociation constant of H₂S is 1.2 × 10^–13, calculate the concentration of S^2– under both conditions. 

Answer 1

(i) To calculate the concentration of HS– ion: 

Case I (in the absence of HCl): 

Let the concentration of HS– be x M. 

Case II (in the presence of HCl): 

In the presence of 0.1 M of HCl, let [ HS^-]  be y M

To calculate the concentration of [S^2-] 

Case I (in the absence of 0.1 M HCl): 

Case II (in the presence of 0.1 M HCl): 

Again, let the concentration of HS– be X' M. 

  (From first ionization, case II) 

                                          (From HCl, case II)