Final answer:
When the pH is below a molecule's pKa, it tends to be in its protonated form. This is seen with functional groups like amino groups in amino acids, which become protonated in acidic conditions.
Step-by-step explanation:
The pH of a solution can influence the protonation state of a molecule. When the pH of a solution is lower than the molecule's pKa, the molecule tends to be in its protonated form. This is because at a pH below the pKa, the environment is acidic enough to promote protonation, whereas at a pH above the pKa, the environment is more basic and protons are less likely to associate with the molecule, leading to a deprotonated form. Amino acids, for example, have specific functional groups that can gain or lose protons depending on the pH of their environment. Their amino (-NH2) groups get protonated to form -NH3+ under acidic conditions when the pH is below their pKa, while their carboxylic (-COOH) groups tend to lose a proton to form -COO- in basic conditions, when the pH is above their pKa.