Using the acid dissociation constants for alanine (K_a1 = 5.1 × 10−³ and K_a2 = 1.8 × 10−¹⁰),calculate the [Z]/[A−] ratio at pH 11.50.(Z = Zwitterion,A− = deprotonated anion)

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At pH = 11.50, the amino group (pKa1 = 5.1) will be deprotonated, and the carboxyl group (pKa2 = 1.8) will still be protonated. Therefore, the alanine will have a net negative charge. However, at this pH, there will still be some alanine molecules that have lost a proton from the carboxyl group, but not from the amino group, resulting in a zwitterion (a molecule with both positive and negative charges). The [Z]/[A-] ratio can be calculated using the Henderson-Hasselbalch equation:
[Z]/[A-] = 10^(pKa1 - pH)/10^(pH - pKa2) = 10^(5.1 - 11.5)/10^(11.5 - 1.8) = 1.8 × 10^-2.
Therefore, the correct answer is C.

Using the Acid Dissociation Constants for Alanine (Ka1 = 5

Using the Acid Dissociation Constants for Alanine (K_a1 = 5