Aquatic Chemistry 367 Civil and Environmental Engineering Meeting time: MWF 11:00-11:50am Meeting room: Abbott Auditorium in Pancoe Pavillion Instructor: Jean-Francois Gaillard jf-gaillard@northwestern.edu Grader: Amy Dahl a-dahl@northwestern.edu 11/8/2018

Species in water Soluble Species Soluble Species Suspended Particles Small Complexes Small Complexes Particles Particles • • Colloidal, aggregates Colloidal, aggregates e.g., e.g., Inorganic Inorganic • • Oxides (Al, Fe, Mn, Si) Oxides (Al, Fe, Mn, Si) Metal Complex Metal Complex • • Adsorption: surface Adsorption: surface Me(CO Me(CO ) ) y y - - complexation complexation 3 3 n n Hydrated Ion Me n+ (H 2 O) n • • Co Co - - entrainment entrainment Hydrated Hydrated Ion Ion Me Me n+ n+ (H (H O) O) 2 2 n n Living Organisms Living Organisms • • Intra/extra Intra/extra - - cellular cellular Complexes with Complexes with • • Oligoelements Oligoelements Macromolecules Macromolecules • • Toxicity Toxicity e.g., Fulvic Acid e.g., Fulvic Acid • • Defense Mechanisms Defense Mechanisms Sediments Sediments! 11/8/2018 e.g., amorphous or crystalline solids (precipitates and mineral formation) e.g., amorphous or crystalline solids

Species in water Dissolved ions: Particulate Major Cations (Ca2+, Na+, Mg2+, K+, Fe2+ or Fe3+) Trace elements (Zn2+, Cr3+, Cu2+, Cd2+) Anions (HCO3-, F-, Cl-, NO3-, SO42-) Non-charged (SiO) Organic molecules (humic substances) http://www.ar.wroc.pl/~weber/kwasy2.htm Particulate Organic matter Clays Oxides 11/8/2018

Chemical Reactions Acid-base chemistry Coordination chemistry H2CO3  H+ + HCO3- Coordination chemistry Hg2+ + Cl-  HgCl+ Precipitation and dissolution ZnS(s)  Zn2+ + S2- Redox reactions 4Fe2+ + O2 +4H+  4Fe3+ + 2H2O 11/8/2018

Thermodynamic explanation Assumes equilibrium of a reaction is reached Simplifies solving mathematical expressions of chemical systems Use an equilibrium constant, K, to describe ratio of products to reactants: aA + bB  cC +dD K = [C]c[D]d/[A]a[B]b 11/8/2018

Chemical Accounting - Concentration Mass concentration Mass of substance/volume of solution mg/L or mg/L Mass of substance/mass of solution mg/kg = ppm or mg/kg = ppb When 1ml = 1g (density = 1): 1 mg/L = 1 ppm and 1 mg/L = 1 ppb 11/8/2018

Chemical Accounting - Concentration Molar concentration (M) – MOST IMPORTANT!!! Molarity = moles of solute per volume solution in liters Molality = moles of solute per mass of solvent in kg 11/8/2018

Chemical Accounting - Concentration Normal concentration (N) 1N = 1 equivalent per liter Based on ion charge Ca2+ + CO32-  CaCO3(s) 2 equivalents per mol Ca2+ Based on Acid-base reaction H3PO4  3H+ + PO43- 3 equivalents per mol H3PO4 Based on Redox reaction 4Fe2+ + O2 +4H+  4Fe3+ + 2H2O 4 equivalents per mol O2 11/8/2018

Chemical Accounting Calculating concentrations of all species in a system based on: Mass conservation of all chemical elements Reactions occurring in system Now we will have an EXAMPLE! 11/8/2018

Rules for tableau method Components must be independent: no component should be expressible as a function of other components Reactions much also be independent: no reaction may be obtained as a linear combination of others Number of components equals number of species minus the number of chemical reactions: NC = NS – NR H2O and H+ should always be chosen as components Electroneutrality Condition All positive charges must equal negative charges 11/8/2018