Introduction to Acid Strength

For Allied Health majors, understanding acid strength is about knowing how easily an acid releases its hydrogen ions (protons) into the body's environment.

1. The Strong Acids (Complete Dissociation)

Strong acids are considered "aggressive." When they hit water (or blood), they break apart 100%. In a clinical setting, these are highly corrosive.

Trend: HI > HBr > HCl >> HF

HI (Hydroiodic) & HCl (Hydrochloric): These are very strong.

Clinical Example: HCl is the primary acid in your stomach (gastric acid). It is strong enough to digest proteins, which is why chronic acid reflux can physically damage the esophagus.

2. The Mild Acids (Partial Dissociation)

Weak acids do not break apart completely. They exist in a "tug-of-war" where most molecules stay together.

Acetic Acid: Known commonly as vinegar.

Unlike HCl, we can safely consume acetic acid because it is "mild." Only a tiny fraction of its molecules release their hydrogen ions.

3. Polyprotic Acids: The Multi-Taskers

Some acids have more than one hydrogen ion to give away. They don't give them all up at once; they do it in stages.

Sulfuric Acid (H₂SO₄) - Stepwise Dissociation:

Note: The first proton is released easily (strong), but the second proton is held more tightly (weak).

Clinical Relevance: The Bicarbonate Buffer System in our blood uses Carbonic Acid (H₂CO₃), which is diprotic. This allows the body to fine-tune blood pH levels.

4. Comparing Strength with pKa

The pKa is a mathematical way to see how "tightly" an acid holds onto its hydrogen. The Rule: The lower the pKa, the stronger the acid.