[sjbyrne]

I have 2.4x10^-2 M Na2S.  The reaction is (I think) Na2S + H2O --> H2S + NaOH.  The Ka value for H2S is 9.5x10^-8.  I would know how to solve this reaction if I had the Ka value of Na2S [Ka=x^2/(2.4x10^-2)] but when I have the Ka value for H2S I am not sure.  I would think that I would still use x^2/(2.4x10^-2) because Ka is for the equilibrium and it is still products over reactants, but I tried that and just tried substituting the Ka value of H2S in instead of the Ka value of Na2S and came up with 5.7x10^-5 to be x (which is also the concentration of OH) but I am told is incorrect.  I feel like it might be something to do with the fact that I have NaOH instead of just OH-. How do I solve this problem?

[Borek]

1. What is the question?

2. You don't have NaOH, you don't have Na₂S - it is all happening in water, so all is dissociated first. Go net ionic.

3. No such thing as Ka of Na₂S, Ka is an acid dissociation constant.