The Hydrogen-Ion Concentration of Natural Waters, I. the Relation OfpH To The Pressure Of Carbon Dioxide

Abstract

1. The Henderson-Hasselbalch equation is shown to be entirely applicable to natural waters. 2. The value of pK₁' is dependent on the normal concentration of the metallic kations present in the solution, including those derived from any neutral salts. The relation between pK₁' and this concentration can be represented by a straight line for concentrations up to 1.0 normal. The equation which expresses this relation is pK₁' = 6.52 - 0.53 3√c,where c is the normal concentration of metallic kations. 3. Methods for measuring accurately the pH by colorimetric methods are given. From the pH thus measured the pressure of carbon dioxide with which the solution is in equilibrium can be calculated with great accuracy. 4. By combining the results obtained the pH (corrected, if necessary for salt error by the curve on p. 56) of a solution of bicarbonates of normal concentration (Bik) as determined by the method described on p. 51, is related to the pressure of CO₂ in mm. Hg (pCO₂ with which the solution is in equilibrium by the equation pH = 10.70 - 0.53 8√c + log Bik/pCO₂. 5. Bicarbonates are transformed into carbonates at a very slow rate when the pressure of carbon dioxide in the solution is reduced. The slow rate at which this process occurs accounts for many natural waters having larger amounts of calcium and magnesium bicarbonates held in solution than can be accounted for by the pressure of carbon dioxide with which the solution is in equilibrium.