Is Sulfuric Acid (H₂SO₄) a Strong or Weak Acid?
Is Sulfuric Acid (H₂SO₄) a strong or weak acid?
H2SO4 is a strong diprotic acid. The first dissociation (pKa = -3) is complete. The second dissociation (HSO4- -> SO4^2-, pKa = 1.99) is weak. The sulfate ion is stabilized by resonance across four oxygen atoms.
| Formula | H₂SO₄ |
| Name | Sulfuric Acid |
| Category | Strong acid |
| pKa | -3 |
| Conjugate | Hydrogen sulfate ion (HSO₄⁻) |
| Key Concept | Polyprotic, first dissociation |
Definition
Sulfuric acid is a strong diprotic acid - it can donate two protons. The first dissociation is complete (strong), but the second is weak.
Acidic Proton / Active Site
Both -OH hydrogens are acidic. The first proton is easily donated (pKa -3, strong acid). After losing the first H+, the remaining HSO4- is a weak acid for the second proton.
Conjugate Pair
First: H2SO4 -> HSO4- + H+. Second: HSO4- -> SO4^2- + H+. The sulfate dianion (SO4^2-) has resonance stabilization across all four oxygens.
Strength Classification
pKa1 = -3 (strong, complete dissociation). pKa2 = 1.99 (weak). Sulfuric acid is the most widely used industrial chemical and a common strong acid in chemistry courses.
See acidic protons, conjugate base overlays, and pKa labels on interactive 3D molecules.
Explore Sulfuric Acid's Acid-Base Properties in 3DRelated Topics
Is Hydrochloric Acid Strong or Weak?
Acid-base classification of HCl
Is Hydrobromic Acid Strong or Weak?
Acid-base classification of HBr
Is Acetic Acid Strong or Weak?
Compare with weak acid
Is Ammonia Strong or Weak?
Compare with weak base
Acidity Ranking
Compare acid strength between molecule pairs
Ionic vs Covalent Bonding
Understand how electronegativity affects bond character