pKa Calculator

Your details

A positive number, often very small (e.g. 1.8 x 10^-5 for acetic acid).
Populates Ka or pKa with a well-known reference value.
pKaVery weak acid
5.745
Ka0.0000018
Percent dissociation at half-equivalence50%
[H+] concentration0.000002mol/L
5.745
Strong acid<0Mod. strong0-2Weak acid2-5Very weak5-10Extremely weak10+

Ka = 1.800e-6 converts to pKa = 5.745.

  • pKa and Ka move in opposite directions: a lower pKa means a larger Ka and a stronger acid.
  • Each one-unit drop in pKa represents a tenfold increase in Ka, because the scale is logarithmic.
  • A pKa of 5.74 places this below pH 7, so the acid donates protons fairly readily in water.

Next stepAt a pH equal to the pKa (5.74), the acid is exactly 50% dissociated. This is the ideal pH for a buffer centered on this acid.

 = Powered by OnlyCalculators