Is Carbonic Acid (H₂CO₃) a Strong or Weak Acid?
Is Carbonic Acid (H₂CO₃) a strong or weak acid?
Carbonic acid is formed when CO2 dissolves in water. It is a weak diprotic acid central to blood pH regulation. The bicarbonate/carbonic acid buffer system maintains blood pH at 7.4.
| Formula | H₂CO₃ |
| Name | Carbonic Acid |
| Category | Weak acid |
| pKa | 6.35 |
| Conjugate | Bicarbonate ion (HCO₃⁻) |
| Key Concept | Biological buffer system |
Definition
Carbonic acid forms when CO2 dissolves in water: CO2 + H2O <-> H2CO3. It is a weak acid that plays a central role in biological pH regulation.
Acidic Proton / Active Site
Both -OH hydrogens are acidic. The first dissociation (pKa 6.35) produces bicarbonate (HCO3-). The second (pKa 10.33) produces carbonate (CO3^2-).
Conjugate Pair
H2CO3 -> HCO3- + H+ (bicarbonate). In blood, the CO2/H2CO3/HCO3- system buffers pH near 7.4. Your lungs control CO2 and your kidneys control HCO3-.
Strength Classification
pKa1 = 6.35, a weak acid. It is weaker than acetic acid but stronger than water. Its biological importance far exceeds what its pKa might suggest.
See acidic protons, conjugate base overlays, and pKa labels on interactive 3D molecules.
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