Final answer:
Phenylalanine is the stronger acid than tryptophan because it has a lower pKa value of 1.83, compared to tryptophan's pKa of 2.83.
Step-by-step explanation:
To determine which is the stronger acid between phenylalanine and tryptophan, you can look at their respective pKa values. The pKa is a quantitative measure of acid strength; thus, the lower the pKa value, the stronger the acid. Phenylalanine has a pKa of 1.83, and tryptophan has a pKa of 2.83, indicating that phenylalanine is the stronger acid compared to tryptophan.
It’s also important to understand why phenylalanine with a lower pKa is stronger than tryptophan. Acid strength can be affected by the stability of the conjugate base, where more stable conjugate bases result from stronger acids. Factors affecting the conjugate base's stability include the electronegativity and size of the atom carrying the acidic proton.