Temperature dependence of the diffusion coefficient of 14CO2 in dilute HCI

The temperature dependence of the diffusion coefficients for 14C labeled carbon dioxide gas diffusing in dilute HCl solutions has been measured. The radioactively labeled gas was trapped as it diffused out of unstirred aqueous solutions. The diffusion curves were analyzed according to the mathematical model proposed by Hawke and Parts. The data obtained are from 10 to 20 percent higher than the literature values measured by a variety of techniques. The wide variations in these quoted values may well be due to uncontrolled variations in the pH of the solutions used. It is proposed that our results refer to the diffusion of free CO2 in water whereas almost all other workers have measured the diffusion coefficients in solutions, having a pH greater than 4.0 which are a weighted mean of D/sub CO2/, D/sub HCO3-/, and D/sub CO32-/. Values of E/sub D/ and ΔS* calculated from Eyring's transition-state theory support the decreased interaction between CO2 and water in acid solutions. (U.S.)