At what pH is the amino acid glycine with a K_a of 2.51 × 10^-10 sixty-six (66%)percent dissociated? A)9.60 B)9.89 C)10.10 D)10.60

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For an amino acid like glycine to be 66% dissociated, it means that the pH is at a point where the concentration of the dissociated form is twice that of the undissociated form. This is because at 66% dissociation, 2/3 of the molecules are dissociated, leaving 1/3 undissociated, giving a ratio of 2:1. This situation corresponds to the Henderson-Hasselbalch equation, which is pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the dissociated form and [HA] is the concentration of the undissociated form. When [A-] is twice [HA], log([A-]/[HA]) = log(2) = 0.3. Given that the pKa (which is the -log of the given dissociation constant, KS) is 9.60 (since pKa = -log(2.51 × 10^-10)), the pH at which glycine is 66% dissociated is 9.60 + 0.3 = 9.90, which rounds to 9.89.

At What PH Is the Amino Acid Glycine with a Ka

At What PH Is the Amino Acid Glycine with a K_a