Chapter 16, Problem 6A

Interpretation Introduction

Interpretation: The ion formed when an acid is dissolved in water and the relationship of this ion to water itself needs to be determined.

Concept introduction: An ${\text{H}}^{\text{+}}$ ion is transferred from the $\text{HCl}$ molecule to the water molecule to form ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$ , which is called the hydronium ion.

Answer to Problem 6A

Hydronium ion is formed when acid is dissolved in water and it is a conjugate acid for water itself.

Explanation of Solution

According to the Brønsted−Lowry model, the general reaction that occurs when an acid is dissolved in water can best be represented as an acid (HA) donating a proton to a water molecule to form a new acid (the conjugateacid) and a new base (the conjugate base). $\begin{array}{l}\text{HA}\left(\text{aq}\right)+{\text{H}}_{\text{2}}\text{O}\left(\text{l}\right)\to {\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\left(\text{aq}\right)+{\text{A}}^{\text{-}}\left(\text{aq}\right)\\ \text{Acid}\text{Base}\text{Conjugate}\text{Conjugate}\\ \text{acid}\text{base}\end{array}$

This model emphasizes the significant role of the polar water molecule in pulling the proton from the acid.

Conclusion

The (aq) means the substance is hydrated-it has water molecules clustered around it.