What is the weak base ionization constant (#K_b#) for #HS^-# equal to?

1 Answer
Jul 12, 2017

Answer:

Well #pK_b=10^(14-pK_a)#............; and thus #K_b=1.25xx10^-7#............

Explanation:

Hydrogen sulfide dissociates according to the reaction......

#H_2S(aq) + H_2O rightleftharpoonsHS^(-) + H_3O^+#

Now #K_a(H_2S)=10^(-6.9)=1.25xx10^-7#, and of course #pK_a=6.9#.

In aqueous solution, we know that #pK_a+pK_b=14#

And thus #pK_b=14-pK_a=14-6.9=7.1#

#K_b=10^(-7.1)#...........#=??#

Note that the question SHOULD have quoted at least #pK_(a1)# for #H_2S#. #K_a# and #K_b# are established by measurement; you could not possibly be expected to remember them.