Question

Pick out incorrect statement

• A. In a electrolysis experiment, $\alpha $ -amino acids migrate at the isoelectric point towards electrodes
• B. p-aminobenzenesulphonic acid as a dipolar ion; while p-aminobenzoic acid does not
• C. Sulphanilic acid is soluble in base, but not in acid
• D. $H_{3}\overset{+}{N}CH_{2}COOH$ is more acidic than $RCH_{2}COOH$

Answer 1

Answer: (A)

A. The pH at which Anion = Cation is called isoelectric point. At isoelectric point, $\alpha $ -amino acids do not migrate when electric field is applied.
B. $-SO_{3}H$ is strongly acidic and donates $H^{+}$ to weakly basic arylamino group. ArCOOH is not acidic enough to transfer $H^{+}$ to the arylamino group.
C. In $p-H_{3}\overset{+}{N}C_{6}H_{4}SO_{3},H_{3}\overset{+}{N}$ is acid enough to transfer $H^{+}$ to bases to give the soluble anion, $p-H_{2}N-C_{6}H_{4}SO_{3}.-SO_{3}$ is too feebly basic and cannot accept $H^{+}$ from acids.
D. $\alpha \text{-}\text{H}_{3}\overset{+}{N}$ group increases acidity, because of its electron-withdrawing inductive effect.