Chapter 18, Problem 69A

Identify the conjugate acid-base pairs in the reaction of ${\text{H}}_3{\text{PO}}_4$ with water.

Interpretation Introduction

Interpretation:

The conjugate acid-base pairs in given reaction is to be identified.

Concept introduction:

The concept of conjugate acid-base pair is given by Bronsted-Lowry.

According to it,

Acid is a substance which donate hydrogen ion and Base is a substance which accept hydrogen ion.

When acid donates $H^{+}$, the species form is conjugate base and when base accepts $H^{+}$, the species form is conjugate acid.

Answer to Problem 69A

Conjugate acid: $H_3{O}^{+}$

Conjugate base: $H_{2}P{O}_4{}^{-}$

Explanation of Solution

The equation is:

$H_{3}P{O}_4+H_{2}O\rightleftharpoons H_{2}P{O}_4{}^{-}+H_3{O}^{+}$

Phophoric acid donates hydrogen ions to form $H_{2}P{O}_4{}^{-}$ ion. So $H_{2}P{O}_4{}^{-}$ is conjugate base.

Water accepts proton to form $H_3{O}^{+}$ so $H_3{O}^{+}$ is conjugate acid.