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Topic: pH problem  (Read 3478 times)

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Offline hvard78

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pH problem
« on: April 17, 2011, 06:18:34 PM »
The pKa value for HCN is 9.21. What molar concentration of NaCN is required to make a solution with a pH of 11.75?

I know:
pKa + pKb= 14
so pKb= 4.79
also, Kb= Kw/Ka
so Kb= 1.62*10^-5

Any help is appreciated.
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Offline scientifics

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Re: pH problem
« Reply #1 on: April 17, 2011, 10:17:02 PM »
If you look at your two components, you will see there is a common-ion. This makes it a common-ion effect problem.  What is the balanced equation? From there, you should be able to set up an ICE table.
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Offline AWK

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Re: pH problem
« Reply #2 on: April 18, 2011, 01:44:15 AM »
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Offline Borek

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Re: pH problem
« Reply #3 on: April 18, 2011, 04:09:03 AM »
Quote from: scientifics on April 17, 2011, 10:17:02 PM
If you look at your two components, you will see there is a common-ion. This makes it a common-ion effect problem.  What is the balanced equation? From there, you should be able to set up an ICE table.

There are no two components.
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Offline scientifics

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Re: pH problem
« Reply #4 on: April 18, 2011, 08:53:52 PM »
The two components are your two compounds (HCN and NaCN). Sorry for any confusion.
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