Conjugate Acids and Bases

What does conjugate mean?

For acids and bases, conjugate means having features in common but opposite or inverse to each other.

What are conjugate acids and bases?

From the Brønsted-Lowrty acids/bases definition, a conjugate base is formed when acids donate protons, and a conjugate acid is formed when bases accept protons.

In any given dissociation of an acid (or a hydrogen addition to a base), a new species is created. This species in turn can accept protons (in the case of the acid) called a conjugate base, or a proton can be accepted (in the case of a base) called a conjugate acid. This new species is called a conjugate base (in the case of a dissociated acid) and a conjugate acid (in the case of a dissociated base):

Original form (Acid)	Dissociated/conjugate form
HCl	Cl$^{-}$, the conjugate base

Table 32.1: Acids and Bases: Examples of the conjugate form.

Original form (Base)	Dissociated/conjugate form
NaOH	Na$^{+}$, the conjugate acid

What is the relationship between the strength of an acid/base and the strength of its conjugate?

Table 32.2: Relationship between the strength of an acid/base and the strength of its conjugate.

Strong Acid	$\Longrightarrow$	Weak conjugate base
Strong Base	$\Longrightarrow$	Weak conjugate acid
Weak acid	$\Longrightarrow$	Strong conjugate base
Weak base	$\Longrightarrow$	Strong conjugate acid

How do amino acids exhibit acid-base properties?

Amino acids have a carboxyl group and an amino group, both of which can serve as weak acids or bases as seen in Figure below. The occurrence of either depends on the pH and will be discussed in more depth in the organic chemistry Amines chapter (on page ) and Amino Acids & Proteins chapter (on page ).

Figure 32.1: Glycine.