The ionization constant of a certain weak is 10−4. What be the [salt] to [acid] ratio if we have to prepare a buffer with pH = 5 using the acid and one of the salts?
A
1 : 10
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B
10 : 1
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C
5 : 4
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D
4 : 5
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Solution
The correct option is B 10 : 1 Given, Ka=10−4,pH=5
According to Henderson-Hasselbalch equation, pH=pKb+log[salt][acid] pH=−logKb+log[salt][acid] 5=−log10−4+log[salt][acid] 5=4+log[salt][acid] log[salt][acid]=1 [salt][acid]=antilog1=10
Hence, the [salt] to [acid] ratio is 10:1