PKa of NaHCO3

Answer 1

The pKa value for sodium bicarbonate (NaHCO3) is 10.3. This provides a measure of the acid strength of bicarbonate.

People often make the mistake of reporting the pKa value of 6.3 for bicarbonate. However, that is the pKa value of carbonic acid (not bicarbonate). It relates to the ease of the first deprotonation of carbonic acid to form bicarbonate. The pKa of bicarbonate relates to the deportation of bicarbonate to form carbonate. This distinction is important, since carbonic acid has two pKa's, the higher of which represents that second deprotonation.

Answer 2

The pKa of NaHCO3 (sodium bicarbonate) is approximately 6.4. This means that at pH values below 6.4, bicarbonate ions will tend to pick up a proton and act as a weak acid, while at pH values above 6.4, bicarbonate ions will tend to lose a proton and act as a weak base.