Online pH calculator of Weak Acids

Weak acids show much higher pH values compared to strong acids. By using this online calculator, you can calculate pH value and H+ concentration of weak acids such as acetic acid (CH3COOH), formic (HCOOH) and more. There are lot of weak acids and their acidic strength depends on the dissociation constant value (Ka). You have to choose the weak acid and give the concentration of acid, calculator will calculate the pH value for you.

Assumptions made during the pH calculator of aqueous weak acid solution

Dissociation constant values (Ka) of weak acids are varied with the temperature and Ka values were taken at 250C temperature in this calculator. Also, assumed that, dissociation of water is negligible compared to dissociation of weak acids. If weak acid concentration is very much low such as 0.00000001 mol dm-3, pH value is approximately close to the neutral state.


Calculation steps in this calculator

  • When pH value of a dibasic weak acid is calculated, second dissociation is neglected because dissociation constant of second dissociation is much less than dissociation constant of first dissociation.If we say it in another way, second dissociation step give much less H3O+ concentration compared to H3O+ concentration given by first dissociation step.
  • Water dissociation is neglected because it is very weak than most of the weak acids.

Calculating pH of weak acid

Calculating pH of weak acid is not easy as calculating pH of a strong acid. You need to know the dissociation constant of weak acid for calculation.

Can I use this calculator for strong acids?

Strong acids readily and completely dissociates to Hydronium cations and respective anion. So, there is no important application of dissociation constant in pH calculation for strong acids as weak acids.