Is Nitric Acid (HNO₃) a Strong or Weak Acid?
Is Nitric Acid (HNO₃) a strong or weak acid?
HNO3 is a strong acid. Its conjugate base (NO3-) is extremely stable because the negative charge is delocalized across three equivalent oxygen atoms via resonance.
| Formula | HNO₃ |
| Name | Nitric Acid |
| Category | Strong acid |
| pKa | -1.4 |
| Conjugate | Nitrate ion (NO₃⁻) |
| Key Concept | Resonance-stabilized conjugate base |
Definition
Nitric acid is a strong monoprotic acid. It donates its -OH proton completely to water.
Acidic Proton / Active Site
The hydrogen on the -OH group is the acidic proton. The N-O-H bond breaks to release H+.
Conjugate Pair
HNO3 -> NO3- + H+. The nitrate ion has three equivalent resonance structures, spreading the charge equally across all three oxygens. This exceptional stability is why HNO3 is a strong acid.
Strength Classification
pKa = -1.4. HNO3 dissociates completely. The resonance stabilization of NO3- (3 equivalent structures) makes the conjugate base so stable that the equilibrium lies entirely to the right.
See acidic protons, conjugate base overlays, and pKa labels on interactive 3D molecules.
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