Multiple Choice
What is the percent dissociation of glycine if the solution has a pH of 8.60 and a pKa of 9.60?
17. Acid and Base Equilibrium
pH of Weak Acids
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At what pH is the side chain of lysine 35% ionized?
A
pH 10.5
B
pH 11.0
C
pH 12.0
D
pH 9.0
Verified step by step guidance1
Understand that the ionization of the side chain of lysine is related to its pKa value. Lysine has a side chain with a pKa around 10.5, which is important for calculating the degree of ionization.
Use the Henderson-Hasselbalch equation to relate the pH, pKa, and the degree of ionization. The equation is:
Recognize that 35% ionization means that 35% of the lysine side chains are in the deprotonated form (A-), and 65% are in the protonated form (HA). Therefore, the ratio [A-]/[HA] is 0.35/0.65.
Substitute the values into the Henderson-Hasselbalch equation:
Calculate the logarithmic term and add it to the pKa value to find the pH at which the side chain of lysine is 35% ionized.
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