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How do I find the concentration of OH- in this reaction?
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Topic: How do I find the concentration of OH- in this reaction? (Read 6059 times)
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sjbyrne
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How do I find the concentration of OH- in this reaction?
«
on:
April 08, 2010, 08:07:56 PM »
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?
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Borek
Mr. pH
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Re: How do I find the concentration of OH- in this reaction?
«
Reply #1 on:
April 09, 2010, 03:15:47 AM »
1. What is the question?
2. You don't have NaOH, you don't have Na
2
S - it is all happening in water, so all is dissociated first. Go net ionic.
3. No such thing as Ka of Na
2
S, Ka is an
acid
dissociation constant.
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ChemBuddy
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How do I find the concentration of OH- in this reaction?