A compound with the condensed formula HOOC–(CH ) –NH(CH ) contains both a carboxylic…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A compound with the condensed formula HOOC–(CH2)3–NH(CH3)2 contains both a carboxylic acid group and a tertiary amine group. The pKa of the carboxylic acid proton is 4.9, and the pKa of the conjugate acid of the tertiary amine (i.e., its pKb-related value) is 10.6.
Respond to the following.
(a) Identify the site that will act as the strongest Brønsted–Lowry acid and the site that will act as the strongest Brønsted–Lowry base in the molecule. Explain your choices using the given pKa values.
(b) Write the net ionic equation for the reaction of one mole of the compound with an excess of 0.10 M HCl(aq).
(c) Write the net ionic equation for the reaction of one mole of the compound with an excess of 0.10 M NaOH(aq).
(d) Predict the predominant ionic form of the compound in aqueous solution at pH 2, pH 7, and pH 12. For each pH value, justify your answer quantitatively or qualitatively in terms of the relative magnitudes of pH and the two pKa values.
(e) Discuss how intramolecular electrostatic attractions or repulsions might influence the molecule’s overall conformation at pH 7. Relate your discussion to the acid–base behavior analyzed in part (d).