Chapter 8, Problem 8.1P

(a)

Interpretation Introduction

Interpretation:

The conjugate acid-base pairs for the reversible reaction of formic acid with cyanide ion have to be identified.

Concept Introduction:

Bronsted-Lowry acid: According to Brønsted-Lowry theory, an acid is a proton donor.

Bronsted-Lowry base: According to Brønsted-Lowry theory, a base is a proton acceptor.

When a Brønsted-Lowry acid donates a proton to a Brønsted-Lowry base, the base that

accepts the proton becomes a conjugate acid.  Contrastingly, the acid that donated the

proton becomes a conjugate base.

    $\begin{array}{l}\text{HX}\text{+}\text{Y}\rightleftharpoons {\text{HY}}^{\text{+}}\text{+}{\text{X}}^{\text{-}}\\ \text{Acid}\text{Base}\text{Conjugate}\text{acid}\text{Conjugate}\text{base}\\ \\ {\text{HY}}^{\text{+}}\text{and}\text{Y}\text{are}\text{Conjugate}\text{acid-base}\text{pair}\\ \\ \text{HX}\text{and}{\text{X}}^{\text{-}}\text{are}\text{Conjugate}\text{acid-base}\text{pair}\end{array}$

Explanation of Solution

Since formic acid is a Bronsted-Lowry acid, it donates proton when it reacts with cyanide ion.  The chemical reaction of formic acid with cyanide and conjugate acid-base pairs are given by

    $\begin{array}{l}{\text{CN}}^{\text{-}}\text{+}\text{HCOOH}\rightleftharpoons \text{HCN}\text{+}{\text{HCO}}_{\text{2}}{}^{\text{-}}\\ \\ \text{HCOOH}\text{and}{\text{HCO}}_{\text{2}}{}^{\text{-}}\text{conjugate}\text{acid-base}\text{pair}\\ \\ \text{HCN}\text{and}{\text{CN}}^{\text{-}}\text{conjugate}\text{acid-base}\text{pair}\end{array}$

(b)

Interpretation Introduction

Interpretation:

The conjugate acid-base pairs for the reversible reaction of methyl amine with water have to be identified.

Concept Introduction:

Refer to part (a).

Explanation of Solution

Since methyl phosphate ion is a Bronsted-Lowry base, it accepts proton when it reacts with water.  The chemical reaction between phosphate ion and water and conjugate acid-base pairs are given by

    $\begin{array}{l}{\text{PO}}_{\text{4}}{}^{\text{3-}}\text{+}{\text{H}}_{\text{2}}\text{O}\rightleftharpoons {\text{HPO}}_{\text{4}}{}^{\text{2-}}\text{+}{\text{OH}}^{\text{-}}\\ \\ {\text{PO}}_{\text{4}}{}^{\text{3-}}\text{and}{\text{HPO}}_{\text{4}}{}^{\text{2-}}\text{are}\text{conjugate acid-base pair}\\ \\ {\text{H}}_{\text{2}}\text{O}\text{and}{\text{OH}}^{\text{-}}\text{are}\text{conjugate acid-base pair}\end{array}$

(c)

Interpretation Introduction

Interpretation:

The conjugate acid-base pairs for the reversible reaction of sulphite ion with hydroxide ion have to be identified.

Concept Introduction:

Refer to part (a).

Explanation of Solution

Since sulphate ion is a Bronsted-Lowry acid, it donates proton when it reacts with hydroxide.  The chemical reaction between sulphite ion with hydroxide ion and conjugate acid-base pairs are given by

    $\begin{array}{l}{\text{HSO}}_3{}^{\text{-}}\text{+}{\text{OH}}^{\text{-}}\rightleftharpoons {\text{SO}}_3{}^{\text{2-}}\text{+}{\text{H}}_{\text{2}}\text{O}\\ \\ {\text{PO}}_{\text{4}}{}^{\text{3-}}\text{and}{\text{HPO}}_{\text{4}}{}^{\text{2-}}\text{are}\text{conjugate acid-base pair}\\ \\ {\text{H}}_{\text{2}}\text{O}\text{and}{\text{OH}}^{\text{-}}\text{are}\text{conjugate acid-base pair}\end{array}$