Chapter 17, Problem 65E

Interpretation Introduction

Interpretation:

Whether a Brønsted-Lowry acid-base reaction between ${\text{OH}}^{-}$ and ${\text{NH}}_{\text{3}}$ is possible or not is to be predicted. If the reaction does not take place, then the reason for the same is to be stated. If the reaction takes place, then the corresponding reaction is to be stated.

Concept introduction:

According to Brønsted-Lowry theory, acids are the substances, which when added to water, donate ${\text{H}}^{\text{+}}$ ions and bases are substances, which when added to water, accept ${\text{H}}^{\text{+}}$ ions.

Answer to Problem 65E

Yes, a Brønsted-Lowry acid-base reaction between ${\text{OH}}^{-}$ and ${\text{NH}}_{\text{3}}$ is possible. The corresponding reaction is shown below.

${\text{OH}}^{-}+{\text{NH}}_{\text{3}}\to {\text{H}}_{\text{2}}\text{O}+{\text{NH}}_{\text{2}}{}^{-}$

In the reaction given above, ${\text{H}}_{\text{2}}\text{O}$ molecule is the conjugate acid of the Brønsted base ${\text{OH}}^{-}$ and the ${\text{NH}}_{\text{2}}{}^{-}$ ion is the conjugate base of the Brønsted acid ${\text{NH}}_{\text{3}}$.

${\text{OH}}^{-}+{\text{NH}}_{\text{3}}\to {\text{O}}^{2-}+{\text{NH}}_{\text{4}}{}^{+}$

In the reaction given above, ${\text{NH}}_{\text{4}}{}^{+}$ ion is the conjugate acid of the Brønsted base ${\text{NH}}_{\text{3}}$ and the ${\text{O}}^{2-}$ ion is the conjugate base of the Brønsted acid ${\text{OH}}^{-}$.

Explanation of Solution

According to Brønsted-Lowry theory, the substances from which an ${\text{H}}^{\text{+}}$ ion, that is a proton, can be removed are known as acids and the substances that are capable of removing an ${\text{H}}^{\text{+}}$ ion from another compound are known as bases.

The compound ${\text{NH}}_{\text{3}}$ possesses an ${\text{H}}^{\text{+}}$ ion, that is a proton. The hydroxide ion $\left({\text{OH}}^{-}\right)$ has the capability to remove the ${\text{H}}^{\text{+}}$ ion from ${\text{NH}}_{\text{3}}$. Therefore, ${\text{NH}}_{\text{3}}$ acts as the Brønsted acid and ${\text{OH}}^{-}$ acts as the Brønsted base. The corresponding chemical reaction is given below.

${\text{OH}}^{-}+{\text{NH}}_{\text{3}}\to {\text{H}}_{\text{2}}\text{O}+{\text{NH}}_{\text{2}}{}^{-}$

In the above reaction, ${\text{H}}_{\text{2}}\text{O}$ molecule is the conjugate acid of the Brønsted base ${\text{OH}}^{-}$ and the ${\text{NH}}_{\text{2}}{}^{-}$ ion is the conjugate base of the Brønsted acid ${\text{NH}}_{\text{3}}$.

It can also be considered that the ${\text{OH}}^{-}$ ion has an ${\text{H}}^{\text{+}}$ ion and the ${\text{NH}}_{\text{3}}$ molecule possesses a lone pair of electrons. The ${\text{NH}}_{\text{3}}$ molecule has the capability to remove the ${\text{H}}^{\text{+}}$ ion from ${\text{OH}}^{-}$ ion. Therefore, ${\text{NH}}_{\text{3}}$ acts as the Brønsted base and ${\text{OH}}^{-}$ acts as the Brønsted acid. The corresponding chemical reaction is given below.

${\text{OH}}^{-}+{\text{NH}}_{\text{3}}\to {\text{O}}^{2-}+{\text{NH}}_{\text{4}}{}^{+}$

In the above reaction, ${\text{NH}}_{\text{4}}{}^{+}$ ion is the conjugate acid of the Brønsted base ${\text{NH}}_{\text{3}}$ and the ${\text{O}}^{2-}$ ion is the conjugate base of the Brønsted acid ${\text{OH}}^{-}$.

Conclusion

Yes, a Brønsted-Lowry acid-base reaction between ${\text{OH}}^{-}$ and ${\text{NH}}_{\text{3}}$ is possible.

The reaction in which ${\text{H}}_{\text{2}}\text{O}$ molecule acts as the conjugate acid of the Brønsted base ${\text{OH}}^{-}$ and ${\text{NH}}_{\text{2}}{}^{-}$ ion as the conjugate base of the Brønsted acid ${\text{NH}}_{\text{3}}$ is shown below.

${\text{OH}}^{-}+{\text{NH}}_{\text{3}}\to {\text{H}}_{\text{2}}\text{O}+{\text{NH}}_{\text{2}}{}^{-}$

The reaction in which ${\text{NH}}_{\text{4}}{}^{+}$ ion acts as the conjugate acid of the Brønsted base ${\text{NH}}_{\text{3}}$ and ${\text{O}}^{2-}$ ion as the conjugate base of the Brønsted acid ${\text{OH}}^{-}$ is shown below.

${\text{OH}}^{-}+{\text{NH}}_{\text{3}}\to {\text{O}}^{2-}+{\text{NH}}_{\text{4}}{}^{+}$