# How can I calculate the pH of an acid?

May 6, 2014

For strong monoprotic acids, the pH = - log [H+]

For example, HCl is a strong acid. In aqueous solutions, water solutions, the hydrogen ion dissociates from the chloride ion.
This ionization or dissociation is complete.

$$In another words, in 100 molecules of HCl, all the hydrogen ions dissociate from all of the chloride ions to form H+ ions and Cl - ions.

HCl --> H+   +  Cl -


The acid is considered monoprotic because it contains one hydrogen atom.

Since there is a 1 HCl molecule to 1 H+ ion ratio,
The concentration of the acid and the hydrogen ion are the same.

Consider a 0.1 molar HCl solution. This solution ionizes to 0.1 molar H+ ions.

Therefore, if you - log [ 0.1 ] = 1

So the pH is 1