A conjugate acid is formed when a base gains a proton, while a conjugate base is formed when an acid loses a proton. They are related pairs in a chemical reaction, differing by the presence or absence of a proton.
What Is Conjugate Acid?
A conjugate acid is a substance formed when a base accepts a proton (H⁺ ion) during a chemical reaction. This transformation occurs as part of the Bronsted-Lowry acid-base theory, which defines acids as proton donors and bases as proton acceptors.
For example, consider the reaction between ammonia (NH₃) and water (H₂O). In this reaction, ammonia acts as a base by accepting a proton from water:
NH₃ + H₂O → NH₄⁺ + OH⁻
In this equation, ammonia (NH₃) accepts a proton from water (H₂O) to form its conjugate acid, ammonium ion (NH₄⁺). Water, which donates a proton, becomes the conjugate base in this reaction (OH⁻). So, NH₄⁺ is the conjugate acid of NH₃, and OH⁻ is the conjugate base of H₂O. Conjugate acids and bases are essential concepts in understanding acid-base chemistry and pH.
What Is Conjugate Base?
A conjugate base is the species that remains after an acid donates a proton (H+) in a chemical reaction. It is formed by accepting the proton from the acid.
For example, consider the reaction between acetic acid (CH3COOH) and water (H2O)
CH3COOH + H2O ⇌ CH3COO- + H3O+
In this reaction, acetic acid donates a proton
Conjugate acid Vs conjugate base
The main differences between conjugate acid and conjugate base are given below:
| Characteristic | Conjugate Acid | Conjugate Base |
| Definition | Gains a proton (H+) | Loses a proton (H+) |
| Chemical Formula | HA | A- |
| Charge | Positive (+) | Negative (-) |
| Relationship to Base | Forms from a base | Transforms from an |
| acid | ||
| Higher Acidity | Lower pH (more H+) | Higher pH (less H+) |
| Strength | Strong or Weak | Strong or Weak |
| Example | HCl -> Cl- | NH4+ -> NH3 |