Hey everyone! So I have my first inorganic lab this week (Chemistry and Qualitative Analysis of Cations) and two of the questions in the prelab are throwing me for a loop. There is a description of how to do the problems in the lab manual but it never says where the numbers come from so I'm completely lost. The problem is:
At what pH will FeS begin to precipitate if the Fe2+ ion concentration is 0.1M and the H2S concentration is 0.01M? Show all calculations to support your answer.
I know that I have to do a [k1a][k2a]. I have Ka1 = [H30+][HS-]/[H2S]. The manual gives me the answer as 1.0x10-7. There are no numbers though or anything so I'm really confused as how it gets the number. I have Ka2 = [H30+][S2-]/[HS-2].
As I said before I think I have the right approach to this but I have no idea where the numbers would come from, if anyone could shed a little insight, it would be wonderful.