2024 H2 Chem P1 Q26 — Nitrogen Compound Solution

The answer is A (anion).
In water, aminoethanoic acid exists mainly as the zwitterion, \(\text{H}_3\text{N}^+\text{CH}_2\text{COO}^-\); its carboxyl group is already ionised.
Adding excess \(\text{OH}^-\) removes \(\text{H}^+\) from the \(-\text{NH}_3^+\) group:
\(\text{H}_3\text{N}^+\text{CH}_2\text{COO}^- + \text{OH}^- \rightarrow \text{H}_2\text{NCH}_2\text{COO}^- + \text{H}_2\text{O}\)
So the concentration of the anion, \(\text{H}_2\text{NCH}_2\text{COO}^-\), increases.
• B is wrong: the cation, \(\text{H}_3\text{N}^+\text{CH}_2\text{COOH}\), forms when acid is added (low pH), not base.
• C is wrong: removing \(\text{H}^+\) from the zwitterion gives the anion, not the uncharged molecule \(\text{H}_2\text{NCH}_2\text{COOH}\).
• D is wrong: the zwitterion is the species being used up, so its concentration decreases.