아미노산 세린 pKa 9.15 ratio 50.0 pH

아미노산 세린 pKa 9.15 ratio 50.0 pH

amino acid serine pKa 9.15 ratio 50.0 pH

 

 

The pKa of the amine group of the amino acid serine is 9.15.

A) What is the pH of a solution

where the ratio of the acidic form of serine to the basic form of serine is 50.0?

B) What is the percent dissociation of serine at the pH in part A?

 

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A)

Henderson-Hasselbalch 식

pH = pKa + log([짝염기]/[약산])

( 참고 https://ywpop.tistory.com/1926 )

 

= 9.15 + log(1 / 50.0)

= 7.45

 

 

 

B)

7.45 = 9.15 + log([A^-]/[HA])

 

log([A^-]/[HA]) = –1.70

 

[A^-]/[HA] = 10^(–1.70) = 0.01995

 

 

 

HA(aq) ⇌ H^+(aq) + A^-(aq)

HA : A^- = 1 : 1 계수비(= 몰수비) 이므로,

이온화된(감소된) HA의 몰수 = 생성된 A^-의 몰수 = x

 

 

 

처음 HA의 양을 1이라 두면, 평형에서

> HA의 양 = 1 – x

> A^-의 양 = x

 

 

 

[A^-]/[HA] = 0.01995

x / (1 – x) = 0.01995

 

x = 0.01995 – 0.01995x

 

1.01995x = 0.01995

 

x = 0.01995 / 1.01995 = 0.0196

---> 0.0196 × 100 = 1.96%