Calculate the pH at which the amino group of lysine is 20% dissociated. lysine side chain pka is 10.5.
9.9
I thought lysine had two amino groups.
http://en.wikipedia.org/wiki/Lysine
it does, its the ε-amino group that i was referring to
To calculate the pH at which the amino group of lysine is 20% dissociated, we need to use the Henderson-Hasselbalch equation. This equation relates the pH of a solution to the pKa and the ratio of the concentrations of the conjugate acid and base forms.
The pKa of the lysine side chain is given as 10.5, which corresponds to the dissociation constant of the amino group. We are trying to find the pH at which 20% of the amino group is dissociated, so we need to determine the ratio of the conjugate acid (dissociated form) to the conjugate base (undissociated form). Since the percentage dissociation is given, we can assume it's also the percentage of the conjugate acid.
To calculate the ratio, we can use the formula:
Conjugate Acid/Conjugate Base = 20%/80% = 1/4
Now, we can insert the known values into the Henderson-Hasselbalch equation:
pH = pKa + log(Conjugate Acid/Conjugate Base)
pH = 10.5 + log(1/4)
pH = 10.5 - log(4)
pH = 10.5 - 0.602
pH ≈ 9.898
Therefore, the pH at which the amino group of lysine is 20% dissociated is approximately 9.898.