Chapter 6, Problem 6A.1AST

(a)

Interpretation Introduction

Interpretation:

The conjugate acid of ${\text{OH}}^{-}$ has to be given.

Concept Introduction:

Conjugate acid of a base has one more proton than its base.  Simply add a proton to the base to get its conjugate acid.

Conjugate base of an acid has one less proton than its acid.  Simply remove a proton from the acid to get its conjugate base.

Explanation of Solution

The given base is ${\text{OH}}^{-}.$

    ${\text{OH}}^{\text{-}}\stackrel{\text{accepts}{\text{H}}^{\text{+}}}{\to }{\text{H}}_{\text{2}}\text{O}$

Now, add a proton to the given base to get its conjugate acid.  Then, the conjugate acid of the given base is ${\text{H}}_{\text{2}}\text{O}\text{.}$

(b)

Interpretation Introduction

Interpretation:

The conjugate base of ${\text{HPO}}_{\text{4}}{}^{2-}$ has to be given.

Concept Introduction:

Refer to part (a).

Explanation of Solution

The given acid is ${\text{HPO}}_{\text{4}}{}^{2-}$

  ${\text{HPO}}_{\text{4}}{}^{2-}\stackrel{\text{donates}{\text{H}}^{\text{+}}}{\to }{\text{PO}}_{\text{4}}{}^{2-}$

Now, remove a proton from the given acid to get its conjugate base.  Then, the conjugate base of the given acid is ${\text{PO}}_{\text{4}}{}^{2-}.$