Weak and strong acids in the surface waters of the tovdal region in S. Norway

Abstract

The concentrations of weak and strong acids in surface waters of the Tovdal region of southern Norway were measured during a spring snow-melt period. The determinations were made by the pH titration method due to Gran. The strong acid concentrations in Tovdal river water varied between 3 and 11 μeq 1 −1, while the weak acid concentrations were between 62 and 106 μeq 1 −1 and the contribution of the weak acids to the hydrogen ion concentration ranged between 10 and 60%. The pH of the river water varied from 4.9 to 5.0 and in the absence of excess strong acid, the weak acids would have produced a pH of 5.2–5.3. The concentration of weak acids and their contribution to the hydrogen ion concentration were least during the period of most rapid thaw. No direct evidence of the nature of the weak acids was obtained, but routine chemical analysis data suggested that inorganic species derived from aluminium and silicon accounted for 40–60 μeq 1 −1, while 20–50 μeq 1 −1 were attributable to humic and fulvic acids. The titration characteristics of the weak acids could be approximated closely by a polybasic acid with a first ionization constant in the range 10 −6 to 5 × 10 −7 and less well defined weaker ionizations. Measurements on old snow containing coniferous tree litter and on melt water from a rocky barren contained weak acid concentrations comparable to the riverwater, indicating that only slight contact with vegetable matter or the ground is required to obtain significant concentrations of weak acids.