Carbonic acid and lactic acids are two of the most important simple carboxylic acids present in our blood. While the chemistry and biochemistry of lactic acid is well known and well understood it is not so with carbonic acid which stilll remains largely an  illusive chemical compound due to its rapid decomposition in aqueous solutions to CO2 and H2O.We have measured the relative basicity of the  bicarbonate and lactate anions by constructing a reactive series of the reaction R1*OH + -OOR2 = R1*O- + HOOR2 where R1*OH is a suitable photoacid and the proton acceptor is the anion of a naturally occuring acid in the blood system.We have found out by a way of direct comparison that the lactate anion is a stronger base than the bicarbonate anion placing the pKa of the carbonic acid below  the known pKa value of lactic acid. Using free-energy correlations the pKa of carbonic acid was found to be 3.48� 0.1 in support of previous measurements by Adamczyk et al. (K. Adamczyk, M. Pr�mont-Schwarz, D. Pines, E. Pines and E. T. J. Nibbering. Real-time observation of carbonic acid formation in aqueous solution, Science, 326 (2009) 1690) but in odd with some other measurements which pointed out to carbonic acid   beeing a weaker acid.

Carbonic acid is stronger acid than lactic acid

248th National Meeting (2014)

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