1. Overview of Some Chemistry in Natural Waters Gases dissolve according to Henry’s law: K H =[X(aq)]/P X ; X=O 2, CO 2, H 2 S, SO 2, etc.  Oxidation-Reduction, Acid-Base, Anaerobic digestion According to pH, can get leaching (dissolution) of various species from soil or rock.

2. Dissolved Oxygen: At 25°C, Henry’s law gives 8.7 mg/l, or 8.7 ppm. Note: This is small, changes greatly with temperature; thermal pollution can lower it significantly. In acid: O 2 + 4H + + 4e -  2 H 2 O In base: O 2 + 2 H 2 O + 4e -  4OH - General example for oxidation of organics: C n H 2n O m + kO 2  nCO 2 + nH 2 O Measure of organic content in water: Biochemical Oxygen Demand (BOD) (Microbial action) Chemical Oxygen Demand (COD) (Na 2 Cr 2 O 7 / H 2 SO 4 ) Total Organic Carbon (Typ. ~1 mg/l, 1 ppm C, in ground water) Dissolved Organic Carbon (Typ. ~5 ppm in surface waters)

3. The pE scale: Analogous to pH; measure of extent to which waters are reducing in nature. pE=-log[e - ] effective, i.e. -log of the activity of e -. Low pE=strongly reducing (more e - s available) High pE=weakly reducing (fewer e - s available)

5. Alkalinity: A measure of the actual concentration of the basic anions in solution as carbonate. total alkalinity = 2[CO 3 2- ]+[HCO 3 - ]+[OH - ]-[H + ] For total alkalinity, the titration is done to Methyl Orange endpoint, pH = 4. For Carbonate only (i.e., no HCO 3 - ), the titration is done to the phenolphthalein endpoint, pH = 8 to 9 -- “phenolphthalein alkalinity.”

6. Hardness: Measures the total concentration of Ca 2+ and Mg 2+ ions. Titrate with ethylenediaminetetraacetic acid (EDTA) Find the total number of moles of Ca 2+ and Mg 2+ ions, then convert to mass per liter of CaCO 3 that would have the same number of ions. For example, if [Ca 2+ ]+[Mg 2+ ]=0.0010 M then, since m.w. CaCO 3 = 100 g/mol, the hardness value is 0.001  100 = 100 mg /l.