Chapter 17, Problem 9E

Interpretation Introduction

Interpretation:

The conjugate base of $\text{HF}$, and ${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}$, and the conjugate acid of ${\text{NO}}_2^{-}$, and ${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}$ is to be stated.

Concept introduction:

According to Brønsted theory of acids and bases, a substance that donates hydrogen ions $\left({\text{H}}^{\text{+}}\right)$ to any other substance is known as an acid. On the other hand, a substance that accepts hydrogen ions $\left({\text{H}}^{\text{+}}\right)$ is known as base. The species that remains after donating proton by a bronsted acid is known as its conjugate base.

Answer to Problem 9E

The conjugate acid of ${\text{NO}}_2^{-}$, and ${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}$ is ${\text{HNO}}_{\text{2}}$ and ${\text{H}}_3{\text{PO}}_4$ respectively. The conjugate base of $\text{HF}$, and ${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}$ is ${\text{F}}^{-}$ and ${\text{HPO}}_{\text{4}}^{2-}$ respectively.

Explanation of Solution

The conjugate base of $\text{HF}$ is formed when an ${\text{H}}^{+}$ ion is removed from it as shown below.

$\begin{array}{l}\text{HF}\to {\text{F}}^{-}+{\text{H}}^{+}\\ \text{Acid}\text{Conjugate}\text{base}\end{array}$

Therefore, the conjugate base of $\text{HF}$ is ${\text{F}}^{-}$.

The conjugate base of ${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}$ is formed when an ${\text{H}}^{+}$ ion is removed from it as shown below.

$\begin{array}{l}{\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}\to {\text{HPO}}_{\text{4}}^{2-}+{\text{H}}^{+}\\ \text{Acid}\text{Conjugate}\text{base}\end{array}$

Therefore, the conjugate base of ${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}$ is ${\text{HPO}}_{\text{4}}^{2-}$.

The conjugate acid of ${\text{NO}}_2^{-}$ is formed when an ${\text{H}}^{+}$ ion is added to it as shown below.

$\begin{array}{l}{\text{NO}}_2^{-}+{\text{H}}^{+}\to {\text{HNO}}_{\text{2}}\\ \text{Base}\text{Conjugate}\text{acid}\end{array}$

Therefore, the conjugate acid of ${\text{NO}}_2^{-}$ is ${\text{HNO}}_{\text{2}}$.

The conjugate acid of ${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}$ is formed when an ${\text{H}}^{+}$ ion is added to it as shown below.

$\begin{array}{l}{\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}{\text{+H}}^{+}\to {\text{H}}_3{\text{PO}}_4\\ \text{Base}\text{Conjugate}\text{acid}\end{array}$

Therefore, the conjugate acid of ${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}$ is ${\text{H}}_3{\text{PO}}_4$.

Conclusion

The conjugate base of $\text{HF}$, and ${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}$.is ${\text{F}}^{-}$ and ${\text{HPO}}_{\text{4}}^{2-}$ respectively. The conjugate acid of ${\text{NO}}_2^{-}$, and ${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{-}$ is ${\text{HNO}}_{\text{2}}$ and ${\text{H}}_3{\text{PO}}_4$ respectively.