If you performed the calculations correctly, it should have given you the answer. Did you use the x to find the pH, that is did you take that negative logarithm of x? Did you take the inverse log of the pKa value to obtain Ka. This is not a difficult problem at all.
I've never had to consider the autodissociation of water in calculations, unless you are dealing with a very, very, very small initial concentration of ammonium. It is ammonium right? Note that I was replying for the ammonium suggestion (in some cases you were wondering about ammonia, you know that there's a difference right?).
The "very strange pH" indicates that you've failed to solve correctly for the solution. Suggest to me an initial concentration of ammonium, and I'll tell you the pH in a jiffy. You should NOT have to take into account the autodissociation of water in most cases.
|