The formula for the conjugate base of NH4+ is NH3.
Understanding Conjugate Bases in Brønsted-Lowry Theory
In chemistry, specifically under the Brønsted-Lowry definition of acids and bases, a conjugate acid-base pair is formed when an acid donates a proton (H⁺). The species that remains after the acid has lost its proton is called its conjugate base. Conversely, when a base accepts a proton, it forms its conjugate acid.
Key principles:
- Acid: A proton (H⁺) donor.
- Base: A proton (H⁺) acceptor.
- Conjugate Base: Formed when an acid loses a proton.
- Conjugate Acid: Formed when a base gains a proton.
Deriving the Conjugate Base of Ammonium Ion (NH4+)
The ammonium ion, NH4+, acts as a Brønsted-Lowry acid because it can donate a proton (H⁺). When NH4+ donates a proton, its chemical structure changes, resulting in a new, uncharged molecule: ammonia.
Consider the dissociation of NH4+ in water:
NH4⁺(aq) ⇌ H⁺(aq) + NH3(aq)
In this reversible reaction:
- NH4+ is the acid, donating a proton.
- NH3 is the resulting species after NH4+ loses a proton, making it the conjugate base of NH4+.
This relationship is fundamental in understanding the behavior of ammonium salts in aqueous solutions, where NH4+ can slightly acidify the solution by donating protons.
Characteristics of the Conjugate Pair
| Aspect | NH4+ (Ammonium Ion) | NH3 (Ammonia) |
|---|---|---|
| Role | Brønsted-Lowry Acid | Brønsted-Lowry Base |
| Charge | +1 (Cation) | 0 (Neutral Molecule) |
| Protons | Contains 4 hydrogen atoms | Contains 3 hydrogen atoms |
| Behavior | Proton donor | Proton acceptor |
Ammonia (NH3) is a common weak base, widely used in various industrial and household applications. Its ability to accept a proton to form NH4+ makes it crucial in buffer systems, which resist changes in pH.
