How can I calculate the pH of an acid?

1 Answer
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