The acid dissociation constant of #"H"_2"S"# and #"HS"^-# are #10^-7# and #10^-13# respectively. The pH of 0.1 M aqueous solution of #"H"_2"S"# will be?
Disclaimer: Somewhat long answer, but the answer is not as bad as one might think!
To find the
Let's set up some equation using the
This acid will dissociate in two steps. We are given the concentration of
Then we can assume that both of these species are in a 1:1 ratio in the dissociation, allowing us to take the square root to find the concentration of both species:
Now in the second dissociation,
Same principle to find the concentration of
So the combined concentration of
So the second dissocation was so small it did not really impact the pH. I guess if this was a multiple choice exam then you only needed to look at the first dissociation and find the square root of
But it is always good to be thorough :)