Is Hydrochloric Acid (HCl) a Strong or Weak Acid?
Is Hydrochloric Acid (HCl) a strong or weak acid?
HCl is a strong acid that dissociates completely in water. The H-Cl bond is weak enough that the proton is fully donated to water, producing H3O+ and Cl-.
| Formula | HCl |
| Name | Hydrochloric Acid |
| Category | Strong acid |
| pKa | -7 |
| Conjugate | Chloride ion (Cl⁻) |
| Key Concept | Strong acid baseline |
Definition
HCl is a Bronsted-Lowry acid - it donates a proton (H+) to water. As a strong acid, it dissociates completely: every HCl molecule gives up its proton.
Acidic Proton / Active Site
The hydrogen atom bonded to chlorine is the acidic proton. Chlorine is highly electronegative, making this H easily donated.
Conjugate Pair
When HCl donates its proton, it becomes Cl- (chloride ion). This is the conjugate base. The conjugate base of a strong acid is extremely weak - Cl- has no tendency to accept a proton back.
Strength Classification
HCl has a pKa of -7, meaning it dissociates completely. Any acid with pKa < -1.74 is considered strong. There are only 7 common strong acids.
See acidic protons, conjugate base overlays, and pKa labels on interactive 3D molecules.
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