What is the Difference Between Conjugate Acid and Conjugate Base?

The difference between a conjugate acid and a conjugate base lies in the presence or absence of a proton (H⁺) in their structures. In the Brønsted–Lowry definition of acids and bases, a conjugate acid is formed when a proton is added to a base, and a conjugate base is formed when a proton is removed from an acid.

Here are the key differences between conjugate acids and conjugate bases:

1. Formation: A conjugate acid is formed when an acid donates a proton to a base, while a conjugate base is formed when an acid loses a proton during a chemical reaction.
2. Structure: A conjugate acid contains one more H atom and one more + charge than the base that formed it. In contrast, a conjugate base contains one less H atom and one more - charge than the acid that formed it.
3. Reactivity: The strength of an acid is inversely proportional to the strength of its conjugate base. Similarly, the strength of a base is inversely proportional to the strength of its conjugate acid.

For example, during the reaction of bicarbonate ions with water to create carbonic acid and hydroxide ions:

$$HCO3^- + H2O \longrightarrow H2CO3 + OH^-$$

• Bicarbonate ions (HCO₃⁻) are the base, and after gaining a proton from water, they become carbonic acid (H₂CO₃), which is the conjugate acid of HCO₃⁻.
• Water (H₂O) is the acid in this reaction, and after donating a proton to bicarbonate ions, it becomes the hydroxide ion (OH⁻), which is the conjugate base of H₂O.

Identifying conjugate acid-base pairs is essential in understanding the reactivity of acids and bases in various chemical reactions.

Comparative Table: Conjugate Acid vs Conjugate Base

The difference between a conjugate acid and a conjugate base can be understood through the Brønsted-Lowry theory of acids and bases. A conjugate acid is formed when a proton is added to a base, and a conjugate base is formed when a proton is removed from an acid. Here is a table summarizing the differences between conjugate acids and conjugate bases:

In a reaction, an acid donates a proton to a base, forming a conjugate acid and a conjugate base. For example, in the reaction between hydrofluoric acid (HF) and water (H2O), HF donates a proton to H2O, forming fluoride ion (F-) as the conjugate base and hydrofluoric acid (HF) as the conjugate acid.