* pH measures the concentration of hydrogen ions (H+) in a solution. This is a measure of *acidity*, not the total number of acid molecules.
* Acids dissociate in water to release hydrogen ions (H+). The strength of an acid determines how many H+ ions it releases. A strong acid like hydrochloric acid (HCl) will release almost all of its H+ ions, while a weak acid like acetic acid (CH3COOH) will only release a small percentage.
* The pH scale is logarithmic. This means that a change of one pH unit represents a tenfold change in the concentration of H+ ions. For example, a solution with a pH of 3 has ten times the concentration of H+ ions as a solution with a pH of 4.
To summarize:
* pH: Measures the concentration of H+ ions (acidity).
* Total acid molecules: Not directly measured by pH.
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