Chapter 17.6, Problem 17P

Interpretation Introduction

Interpretation:

It should be explained that why aldehydes and ketones react with a weak acid like hydrogen cyanide but do not react with strong acids such as ${\text{HCl or H}}_{\text{2}}{\text{SO}}_{\text{4}}$.

Concept introduction:

Acidity of weak acids can be expressed by ${\text{pK}}_{\text{a}}$.  Smaller the ${\text{pK}}_{\text{a}}$ value, the stronger the acid.

The ${\text{pK}}_{\text{a}}$ values of given acid are as follows.

$\begin{array}{cc}{\text{pK}}_{\text{a}}& \text{Given acid}\\ \text{9}\text{.14}& \text{HCN}\\ \text{-7}\text{.0}& \text{HCl}\\ \text{-5}& {\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}\end{array}$