Question

Identify the conjugate acid-base pairs in the following reactions:

(a)${\mathbf{H}}_{\mathbf{3}}{\mathbf{NCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{NH}}_{\mathbf{3}}\mathbf{+}{\mathbf{H}}_{\mathbf{2}}\mathbf{O}\mathbf{}\mathbf{\rightleftharpoons }\mathbf{}\mathbf{}{\mathbf{H}}_{\mathbf{3}}{\mathbf{NCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{NH}}_{\mathbf{2}}\mathbf{+}{\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$

(b) Benzoicacid+ Pyridine$\mathbf{\rightleftharpoons }$ Benzoate+ Pyridinium

Short answer

(a)

${\mathrm{H}}_3{\mathrm{NCH}}_2{\mathrm{CH}}_2{\mathrm{NH}}_2$ - Conjugate base

${\mathrm{H}}_3{\mathrm{O}}^{+}$- conjugated acid

(b)

Benzoate - conjugate base

Pyridinium - conjugated acid

Step-by-step solution

Definition of Conjugate Acid Base Pairs

By gain or loss of H⁺conjugate acid-bases are related to each other.

Consider acid HA with its corresponding base${\mathbf{A}}^{\mathbf{-}}$ they are collectively known as conjugate acid-base pair since they are associated with gain or loss of proton.

Conjugate base of weak acid is a weak base.

Conjugate acid of weak base is a weak acid.

Definition of Conjugate Acid Base Pairs

(a)

Given reaction is

${\mathrm{H}}_3{\mathrm{NCH}}_2{\mathrm{CH}}_2{\mathrm{NH}}_3+{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{H}}_3{\mathrm{NCH}}_2{\mathrm{CH}}_2{\mathrm{NH}}_2+{\mathrm{H}}_3{\mathrm{O}}^{+}$

By the concept of Bronsted-Lowry acid- base, the base which accepts a proton called conjugated acid and similarly the acid which donates a proton called conjugate base.

Hence, the acid-base pair in this reaction is,

role="math" localid="1663388167770" ${\mathrm{H}}_3{\mathrm{NCH}}_2{\mathrm{CH}}_2{\mathrm{NH}}_2$- conjugate base

${\mathrm{H}}_3{\mathrm{O}}^{+}$- conjugated acid

(b)

Given reaction is

Benzoic acid+ Pyridine $\rightleftharpoons$Benzoate+ Pyridinium

By the concept of Bronsted-Lowry acid- base, the base which accepts a proton called conjugated acid and similarly the acid which donates a proton called conjugate base.

Hence, the acid-base pair in this reaction is

Benzoate - conjugate base

Pyridinium - conjugated acid