The dissociation constants of carbonic acid in seawater at salinities 5 to 45 and temperatures 0 to 45°C

Abstract

The pK1∗ and pK2∗ for the dissociation of carbonic acid in seawater have been determined from 0 to 45°C and S = 5 to 45. The values of pK1∗ have been determined from emf measurements for the cell: Pt](1 − X)H2 + XCO2|NaHCO3, CO2 in synthetic seawater|AgC1; Ag where X is the mole fraction of CO2 in the gas. The values of pK2∗ have been determined from emf measurements on the cell: Pt, H2(g, 1 atm)|Na2CO3, NaHCO3 in synthethic seawater|AgC1; Ag The results have been fitted to the equations: lnK∗1 = 2.83655 − 2307.1266/T − 1.5529413 lnT + (−0.20760841 − 4.0484/T)S0.5 + 0.08468345S − 0.00654208S1 InK∗2 = −9.226508 − 3351.6106/T− 0.2005743 lnT + (−0.106901773 − 23.9722/T)S0.5 + 0.1130822S − 0.00846934S1.5 where T is the temperature in K, S is the salinity, and the standard deviations of the fits are σ = 0.0048 in lnK1∗ and σ = 0.0070 in lnK2∗. Our new results are in good agreement at S = 35 (±0.002 in pK1∗and ±0.005 in pK2∗) from 0 to 45°C with the earlier results of Goyet and Poisson (1989). Since our measurements are more precise than the earlier measurements due to the use of the Pt, H2|AgCl, Ag electrode system, we feel that our equations should be used to calculate the components of the carbonate system in seawater.