Answer:
a. 8.3= pKa of the aminoacid
b. Cysteine
Explanation:
The pH of an acid can be obtained using the H-H equation:
pH = pKa + log [A-] / [HA]
Where pH is the pH of the buffer = 7.0
pKa is the pka of the conjugate acid = ?
[A-] / [HA] is the ratio between conjugate base and conjugate acid. As the ratio of conjugate acid to conjugate base = 20:1, the [A-] / [HA] = 1/20
Replacing:
7 = pKa + log 1/20
7 = pKa - 1.30
7+1.30 = 8.3 = pKa of the aminoacid
The only aminoacid with a side chain with pKa = 8.3 is:
Cysteine. Allowing its identification.
