Equilibrium approaches to natural water systems—Part 2

The apparent equilibrium constant, K ₁ ^′ , for the first acidity constant of carbonic acid has been determined in a lake water of 1.6 mM ionic strength in the temperature interval 4–18°C. The experimental method used comprises pH measurements in situ (NBS scale) with a probe and an IR-method for the selective determination of H₂CO₃] and HCO ₃ ^? ] in water samples. In the temperature interval studied the results can be described by the equation logK ₁ ^′ =126.39?6320.81/T?19.5682 ln T and are in agreement with the values of K ₁ ^′ obtained by the empirical equation presented by Millero 15]. This experimental agreement justifies thermodynamic calculations in the carbonate system based on field data. Also the experimental method described can be used to evaluate the acid-base balance of organic rich natural waters.