The dissociation constant for a previously uncharacterized racemic acid discovered in a meteor have been determined to be pk1=2.0, pk2=3.5, pk3=6.3, pk4=8.0, pk5=9.8, and pk7 = 10.9. A. What carboxyl or functional group would you expect to be associated with each dissociation?

ANSWER:

pK_a is the log of dissociation constant of an acid. Suppose an acid is HA.

HA will dissociate to à H⁺ + A^–

A strong acid will dissociate fast and will have a higher dissociation constant (K_a).

pK_a = -log₁₀ (K_a)………………..(1)

Using the above equation, it is clear that for a lower pKa, Ka value is higher; so, the strong acid will have low pK_a.

Therefore, pk1, pk2, and pk3 are carboxyl groups (i.e. acidic groups); pK4, pK5, and pK7 are amino groups (basic groups).

Plz. note that amino acids have either carboxyl or amino groups associated with their dissociation, nothing else.