Henderson–Hasselbalch식. Ka of the amino acid glutamine

Henderson–Hasselbalch식. Ka of the amino acid glutamine

 

 

Use Henderson–Hasselbalch equation to determine the Ka of the amino acid glutamine if it is 33.0% dissociated at pH = 8.82.

 

What is the Ka of the amino acid glutamine if it is 33.0% dissociated at pH = 8.82?

 

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percent dissociation = {[HA]_dissociated / [HA]_initial} × 100

 

In a buffer solution,

[HA]_dissociated = [A^-]

 

[HA]_initial = [HA]_dissociated + [HA]

= [A^-] + [HA]

 

pH = pKa + log{[A^-]/[HA]}

( [HA], [A^-]는 평형에서의 농도. )
( 즉, [HA]는 평형에서 이온화 안 된 약산의 농도임. )
( 가령, 이온화되기 전에 약산이 100개 있었다면,
( 33.0개 이온화되고, 67.0개 이온화 안 된 것임.)

 

8.82 = pKa + log(33.0/67.0)

8.82 = pKa – 0.308

pKa = 9.128

Ka = 10^(-9.128) = 7.45×10^-10

 

 

답: 7.45×10^-10