Acids and Bases
Conjugate Acid-Base Pairs
A conjugate acid-base pair differs by a single proton ( $ H^+ $ ).
- Acid: A substance that donates a proton ( $ H^+ $ ).
- Base: A substance that accepts a proton ( $ H^+ $ ).
When an acid donates a proton, it forms its conjugate base. When a base accepts a proton, it forms its conjugate acid.
$$ HA \rightleftharpoons H^+ + A^- $$
In this equation:
- $ HA $ is the acid.
- $ A^- $ is its conjugate base.
$$ B + H^+ \rightleftharpoons BH^+ $$
In this equation:
- $ B $ is the base.
- $ BH^+ $ is its conjugate acid.
Examples:
- $ HCl $ (acid) and $ Cl^- $ (conjugate base): $ HCl \rightleftharpoons H^+ + Cl^- $
- $ NH_3 $ (base) and $ NH_4^+ $ (conjugate acid): $ NH_3 + H^+ \rightleftharpoons NH_4^+ $
- $ H_2O $ can act as both an acid and a base (amphoteric):
- As an acid: $ H_2O \rightleftharpoons H^+ + OH^- $ (conjugate base is $ OH^- $ )
- As a base: $ H_2O + H^+ \rightleftharpoons H_3O^+ $ (conjugate acid is $ H_3O^+ $ )
Amphoteric Substances (Water as an Acid and Base)
Acid Strength and Conjugate Base Strength (Base Strength and Conjugate Acid Strength)