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. $H_3\stackrel{+}{N}C{H}_{2}COOH$ is more acidic than $RC{H}_{2}COOH$

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. $-S{O}_{3}H$ 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 $p-H_3\stackrel{+}{N}{C}_6{H}_{4}S{O}_3,H_3\stackrel{+}{N}$ is acid enough to transfer $H^{+}$ to bases to give the soluble anion, $p-H_{2}N-C_6{H}_{4}S{O}_3.-S{O}_3$ is too feebly basic and cannot accept $H^{+}$ from acids.
D. $\alpha \text{-}{\text{H}}_3\stackrel{+}{N}$ group increases acidity, because of its electron-withdrawing inductive effect.