What is pka value for sodium bicarbonate?

There are two answers: bicarbonate has two pKa's - because bicarbonate can gain a proton to become carbonic acid or lose a proton to become carbonate. Two reactions; two pKa's. The pKa for bicarbonate carbonic acid reaction is 6.4 The pKa for bicarbonate carbonate reaction is 10.3 Both pKa's are temperature sensitive.