The Rate of the Dehydration of Carbonic Acid and the Effect of Ionic Strength near Neutral pH

Abstract

The spontaneous dehydration of carbonic acid has been studied at 1.6°C and at 24.8°C. The initial rate of the reaction was measured by means of a pH-stat method.

The effect of ionic strength on the rate of the reaction could be described by the equation: log k'_d = log k_d^o - pH + f_HCO3⁻· k_d' is a 1st order rate constant calculated from the experimental results obtained at a given pH and ionic strength. The value of k_d^o, the 2nd order rate constant for the formation of CO₂ from H⁺ and HCO₃^- at zero ionic strength, was found to be 0.93 · 10⁴ 1 · mole^-1 · sec^-1 at 1.6°C. The contribution from the reaction HCO₃^-→CO₂+OH^- to the total formation of CO₂ at 25°C has been found to be approx. 3 per cent at pH 7 and approx. 25 per cent at pH 8.

Key Words:

• Bicarbonates
• hydrogen-ion concentration
• carbonic anhydrase