Chapter 21, Problem 1TE

Identify the acid or base behavior of each substance in these reactions:

(a) ${\text{H}}_3{\text{O}}^{+}+{\text{Cl}}^{-}\rightleftarrows {\text{H}}_2\text{O}+\text{HCl}$

(b) ${\text{H}}_2{\text{PO}}_4+{\text{H}}_2\text{O}\rightleftarrows {\text{H}}_3{\text{O}}^{+}+{\text{HPO}}_4{}^{-}$

To determine

The acid or base behaviour of all substances in the reaction.

Answer to Problem 1TE

a) The ${\text{H}}_3{\text{O}}^{+}$, ${\text{Cl}}^{-}$, ${\text{H}}_2\text{O}$, and $\text{HCl}$ are behaving as an acid, base, base, and an acid respectively.

b)The ${\text{H}}_2{\text{PO}}_4$, ${\text{H}}_2\text{O}$, ${\text{H}}_3{\text{O}}^{+}$, and ${\text{HPO}}_4{}^{-}$ are behaving as an acid, base, acid, and base respectively.

Explanation of Solution

The acid donates the hydrogen ion/proton while the base accepts it.

a)The ${\text{H}}_3{\text{O}}^{+}$ ion gets transformed into the ${\text{H}}_2\text{O}$ molecule. It loses a hydrogen ion. So, it is behaving as an acid. The hydrogen ion is accepted by the ${\text{Cl}}^{-}$ ion. As it accepts a hydrogen ion, it is behaving as a base. For reverse reaction, the ${\text{H}}_2\text{O}$ molecule accepts a hydrogen ion to get transformed into ${\text{H}}_3{\text{O}}^{+}$, so it behaves as a base. The $\text{HCl}$ molecules donate the hydrogen ion to ${\text{H}}_2\text{O}$, so it behaves as an acid.

b)The ${\text{H}}_2{\text{PO}}_4$ molecule donates the hydrogen ion to the ${\text{H}}_2\text{O}$ molecule, so it behaves as an acid. The ${\text{H}}_2\text{O}$ molecule accepts the hydrogen ion to form ${\text{H}}_3{\text{O}}^{+}$ ion, so it behaves as a base. For reverse reaction, the ${\text{H}}_3{\text{O}}^{+}$ ion donates the hydrogen ion to ${\text{HPO}}_4{}^{-}$ ion, so it behaves as an acid. The ${\text{HPO}}_4{}^{-}$ ion accepts the hydrogen ion to form the ${\text{H}}_2{\text{PO}}_4$ molecule, so it is a base.

Conclusion:

a)Therefore, The ${\text{H}}_3{\text{O}}^{+}$, ${\text{Cl}}^{-}$, ${\text{H}}_2\text{O}$, and $\text{HCl}$ are behaving as an acid, base, base, and an acid respectively.

b)The ${\text{H}}_2{\text{PO}}_4$, ${\text{H}}_2\text{O}$, ${\text{H}}_3{\text{O}}^{+}$, and ${\text{HPO}}_4{}^{-}$ are behaving as an acid, base, acid, and base respectively.