Chapter 16, Problem 5A

Interpretation Introduction

Interpretation: A Brønsted−Lowry acid that forms its conjugate base when dissolved in water and the role of water in this process, are to be determined.

Concept introduction:

Conjugate base: The remaining substance when a proton is lost from an acid is known as conjugate base.

Answer to Problem 5A

The conjugate base is species that remains when an acid molecule lost a proton. In the presence of an acid, water act as a base because it accepts the proton.

Explanation of Solution

According to the Brønsted−Lowry model, when a Bronsted-Lowry acid is dissolved in water, it donates its proton to water molecule and itself gets converted into conjugate base.

The reaction is represented as follows:

  $\text{HCl}\left(\text{aq}\right)+{\text{H}}_{\text{2}}\text{O}\left(\text{l}\right)\to {\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\left(\text{aq}\right)+{\text{Cl}}^{\text{-}}\left(\text{aq}\right)$

In this case, $\text{HCl}$ is an acid that loses an ${\text{H}}^{\text{+}}$ ion to form ${\text{Cl}}^{\text{-}}$ , its conjugate base. On the other hand, ${\text{H}}_{\text{2}}\text{O}$ (behaving as a base) gains an ${\text{H}}^{\text{+}}$ ion to form ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ (the conjugate acid).

Conclusion

In the Brønsted−Lowry model, an acid is a proton ( ${\text{H}}^{\text{+}}$ ) donor and a base is a proton acceptor.