KEY2CHEM

Acid-Base Chemistry

An acid can be defined as a substance that donates a proton (\(\require{mhchem}\ce{H+}\)) to generate hydronium ion (\(\require{mhchem}\ce{H3O+}\)) in aqueous solution. The extent of ionization (dissociation) of an acid determines whether it is classified as a strong acid (fully dissociates) or a weak acid (partially dissociates). The extent of dissociation, particularly of a weak acid, is an equilibrium process.


Example 1.

Which diagram best describes the solution that forms when \(\require{mhchem}\ce{HCl}\) () is dissolved in water (\(\require{mhchem}\ce{H2O}\), )?

 

 

 

A

B. 

C. 

 

 

Solution

B. 

 

\(\require{mhchem}\ce{HCl}\) is a strong acid, which dissociates completely into ions (\(\require{mhchem}\ce{H3O+}\) and \(\require{mhchem}\ce{Cl-}\)) when dissolved in water.


Example 2.

In a \(0.50\text{ M}\) solution of the weak acid acetic acid (\(\require{mhchem}\ce{CH3COOH}\)), which species will have the highest concentration?

 

 

 

A. \(\require{mhchem}\ce{CH3COOH}\)

B. \(\require{mhchem}\ce{H3O+}\)

C. \(\require{mhchem}\ce{OH-}\)

 

 

 

Solution

A. \(\require{mhchem}\ce{CH3COOH}\)

 

A weak acid dissociates only slightly into its ions; most of the acid exists as undissociated molecules.


Example 3.

Which statement about a strong base is true?

 

 

A. A strong base is more harmful than a weak base.

B. A strong base dissociates to a greater extent than a weak base.

C. A strong base is more concentrated than a weak base.

 

 

 

 

Solution

 

B. A strong base dissociates to a greater extent than a weak base.

 

A strong  base dissociates completely into ions while a weak base will generate a smaller than stoichiometric concentration of ions.