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dnpgr16513
Joined: 14 Jun 2010
Posts: 75
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 Posted: Fri Jun 25, 2010 4:48 pm Post subject: |
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Why can't you figure out this problem with
Ka x Kb = Kw?
I assumed you could figure out the Ka, find the log of Ka, which equals pKa. pKa = pH and then after finding the pH I could subtract this from 14. When I do it I get big numbers ( even negative), but I don't know why this approach wouldn't be logical.
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jellywing_2058
Joined: 04 May 2009
Posts: 179
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| Posted: Wed Jul 07, 2010 2:18 pm Post subject: |
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You may calculate the ka, however we are looking at a basic substance CN- and I do not see why one would calculate the Ka?
In addition, once you obtain your Ka, you may obtain the pKa; however, pKa does not always equal pH as per your statement.
Moreover, pKa = pH when the conjugate base concentration equals the acid concentration as per the Henderson Hasselbach equation. So you cannot assume that pKa = pH for all scenarios. |
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