“Save the whales. Collect the whole set” “Plan to be spontaneous tomorrow”

1. “Save the whales. Collect the whole set” “Plan to be spontaneous tomorrow” “Ambition is a poor excuse for not having enough sense to be lazy” “Life is too short not to be in a hurry”

2. U6220: Environmental Chem. & Tox.Thursday, June 16 2004 • Announcement: http://www.columbia.edu/itc/sipa/envp/louchouarn/courses/ • Solutions • Acid-Bases: • Carbonate systems • Alkalinity • The legacy of acid-rain in a changing climate

3. Basic Chemistry Review Polarity of molecules The C-H bond is one of the most common in organic compounds. The electronegativity difference between these two atoms is 0.4 (weakly polar). The electronegativity difference in the O-H bond, however, is 1.4 (polar bond) Dipole bonding results from polar substances in a polar solution (solubility) Apolar molecules will tend to have low solubility in polar solutions

4. The Water (“Mickey Mouse”) Molecule Water: H2O! How simple can that be? Dipole (slightly charged at each end!)  Uneven charge  Hydrogen bonds! Higher energy requirement for change of state (i.e. to “separate” Mickey and Minnie!)

5. Basic Chemistry Review Solubility Solubility of compounds in water (or any other liquid/solvent) influences their dispersal and fate in the environment (water exists in liquid form on land, under land, and in the atmosphere). Solution of an ionic compound in a polar solvent (ie. NaCl in water).

6. C) Basic Chemistry Review Solubility Solubility of nonpolar compounds in nonpolar solvents: “like” dissolves “like” NaCl will NOT dissolve in hexane But PCBs, oil, etc, will! Solubility of nonpolar solutes in water decreases with size of solute

7. Basic Chemistry Review Partition behavior Partition coefficient: Ratio of a concentrations of a chemical in two different phases  organic pollutants - PCBs, PAHs – and lipids how solutes behave with respect to two solvents (polar vs. non polar) The partition coefficient is constant for a given solute and two specific solvents (under constant environmental conditions: T & P) Partition coefficient is dependent on: Polarity of solute Its molecular weight Relationship to the polarity of solvents

8. Basic Chemistry Review Partition behavior Octanol (CH3-(CH2)7-OH)/water partition (imitates lipid/water partition) [C]o = [C]w  Kow Kow = [C]o/[C]w As Kow increases, the “lipophilicity” of a chemical increases Kow for various homologous series is related to molecular surface area  size

9. Solutions

10. Solutions Molarity (M) Moles of solute/Liters of solutions Mass per Volume (g/L) mass of solute/Liters of solutions Mass per Mass (ppm) mass of solute/mass of solutions (g/g) Mass per Mass per Volume (ppmv) percent volume solute/volume of solution

11. Solution Equilibria and Acids Aquatic equilibria are important in environmental processes At equilibrium: aA + bB  cC + dD Kc = [C]c[D]d/[A]a[B]b Where Kc is the equilibrium constant and the right hand of the equation, the equilibrium quotient, is the ratio of products to reactants Le Chatelier Principle (useful indications of shifts in equilibrium): “When a system in equilibrium is subjected to change, the system will alter in such a way as to lessen the effect of that change”  Adding product ‘C’ to the system will make the rxn shift to the left (consumption of ‘C’ and ‘D’) and the position of the equilibrium changes (Kc remains unchanged)

12. Dissociation of water and the pH scale 2H2O H3O+ + OH- or H2O H+ + OH- where Kw = ([H+][OH-]/[H2O])eq Where [H2O] is equal to unity (pure substances) Kw = ([H+][OH- ])eq

13. Dissociation of water and the pH scale Kw = ([H+][OH-]/[H2O])eq Experimental determination shows that Kw = 1.8x10-16 mol/liter (at 25ºC) It is conventional to omit the concentration of water from this K expression. Why? [H2O]eq = 55.5 Molar Why? Kw = 10-14 Why?

14. Dissociation of water and the pH scale Kw = ([H+][OH- ])eq Experimental determination shows that Kw = 10-14 (at 25ºC) log Kw = log 10-14 log Kw = -14  log 10 • log Kw = 14 • pKw = -log Kw So pKw = 14 [H+][OH-] = 1x10-14 and [H+] = [OH-] = 1x10-7 So pH of natural waters = -log [H+] = -log 10-7 = 7

15. Dissociation of water and the pH scale Kw = [H+][OH- ] And for any acid (HB) in solution HB  H+ + B- (Henderson-Hasselbach equation)

16. Dissociation of water and the pH scale For water log Kw = log [H+]+ log [OH-] - log Kw = - log [H+]- log [OH-] pKa = pH + pOH and pH + pOH = 14 For other acids: Ka = [H+][A- ]/[HA] HCl H+ + Cl- where pKa = -3 CH3COOH + H2O CH3COO- + H+ Ka = ([CH3COO-]+[H+])/[CH3COOH] = 10-4.76 pKa = ? pKa = 4.76

17. Dissociation of water and the pH scale For other acids: Ka = [H+][A- ]/[HA] HCl  H+ + Cl- where pKa = - log Ka or Ka = 10-pKa

18. Single variable diagrams Speciation of metals: Species distribution based on environmental conditions What is the most abundant species of iron in natural waters?

19. pH and minerals pH and mineral surface charge The “point of zero charge” (PZC) is point at which a surface charge changes sign pHpzc will influence sorption capacity of minerals (and organic substances) in natural environments

20. Single Variable Diagrams: pH What is the most abundant species of arsenic in natural waters? How does pH influence As distribution?

21. Carbonate system - Acids in the environment CO2(aq) + H2O = H2CO3º (total CO2(aq) + H2CO3) KCO2 = [H2CO3 º]/[PCO2] = 10-1.47 First dissociation step for carbonic acid: K1 = [H+][HCO3- ]/[H2CO3] = 10-6.35 Second dissociation step for carbonic acid: K2 = [H+][CO32- ]/[HCO3-] = 10-10.33

22. Carbonate system - Acids in the environment Dominant carbonate species are related to K1 and K2 H2CO3 dominates below pH = pK1 = 6.35 HCO3-dominates between pH = pK1 = 6.35 & pH = pK2 = 10.33 CO32-dominates above pH = pK2 = 10.33

23. Alkalinity Alkalinity is a measure of the ability of a water body to neutralize acids and is very important in predicting the extent of acidification in natural waters (i.e. lakes and rivers) Alkalinity = [OH-] + [HCO3-] + 2[CO32-] - [H+] ANC = [OH-] + [HCO3-] + 2[CO32-] + [B(OH)4-] + [H3SiO4-] + 2[HPO42-] + [HS-] + [NOM-]- [H+] - 3[Fe3+] - … Contribution of all these species tends to be minimal in natural fresh waters (concentrations are too small. With the exception of NOM!). The alkalinity tends then to be equal to ANC  only proton accepting species, present in substantial concentration, are carbonates and/or hydroxyl ion.

24. Alkalinity Alkalinity is a capacity factor measure of the ability of a water sample to sustain reaction with added acid or base pH is an intensity factor measure of the concentration of protons (acids) immediately available for reaction Buffer capacity: is the capacity of a solution (or water-rock system) to resist pH change when mixed with a more acid or alkaline water (rock)

25. Alkalinity Titration: “a procedure for determining the amount of acid (or base) in a solution by determining the volume of base (or acid) of known concentration that will completely react with it” Acidification of a lake in a natural setting is analogous to a macro-scale titration and lakes are sometimes termed “buffered”, “transitional”, and “acidic” depending on their position on the titration curve:

26. Alkalinity An alternative way to report alkalinity is to express it in terms of neutralization reaction between carbonate and protons and given in values of mg/L of CaCO3 (or mg/L of Ca2+) 1 mg CaCO3 = 1000 g which is 1000 g/100 g/mol = 10 mol Since each carbonate (CO32-) is capable of neutralizing two OH- ions 10 mol of CO32- is equivalent to 20 mol proton-accepting capacity (20 equivalents or eq). A sensitivity classification of water bodies may thus be expressed in terms of alkalinity using units of mol/L of proton accepting capacity (eq)

27. The legacy of acid-rain

28. Coal and Acid rain SO2 + 2OH H2SO4 2H+ + SO42- SO2 + H2O2H2SO4 2H+ + SO42- N2 + O2 2NO (>2000°C) NO + O3 NO2 + O2 NO2 + OH HNO3 H+ + NO3-

29. Acid rain The main sources of acid deposition are emissions from oil and coal-burning power plants and automobiles

30. Acid rain? In the US, seven states in the Ohio valley account for ~40% of all SO2 emissions. (emissions travel downwind to N.E.) Midwest states are the most significant emitters of NOx and NH4

31. Acid rain? In the US, SO2 emissions have been declining since about 1980 (still above background). NOx emissions have not changed

32. Acid rain? Acidity of rain is neutralized by CaCO3

33. Acid rain? Change in stream sulfate concentrations, but delayed! Yellow: wet deposition Blue: surface waters

34. Acid rain? Role of hydrodynamic forcing

35. Spatial Variability of Streamflow (U.S. North East) Large-scale spatial variability in streamflow is explained by precipitation/evaporation balance to a large extent (~90%) and additional processes to a smaller one (soil water storage, seasonality)

36. What are the seasonal predictions for N. America? Seasonal predictions of precipitation for North America. Clockwise from upper left: Winter, Spring, Fall, Summer. Coupled Model Intercomparison Project (CMIP) using 1% CO2 increase per year and the perturbations for the last 20 years of an 80 years run (Ting, pers. Comm.)

37. Drought Temporal and spatial variability

38. Temporal Variability of Streamflow For the Catskill region, the change in evapotranspiration and snowpack amount will offset any increase in precipitation that may occur.

39. What does it mean for acidified lake recovery? • Fluctuations in streamflow patterns (particularly drought incidence) has strong impact of re-acidification of lakes • Increased Al inputs (toxic to aquatic biota) • Decreased pH • Decreased acid neutralizing capacity (ANC)

40. Redox Potential (Acid Mine Drainage) Sulfate reduction: SO42-+ 2CH2O + 2H+ H2S + 2H2O + 2CO2 With the presence of Fe2+ Fe2+ + H2S  FeS + 2H+ And FeS + S  FeS2 Sulfide oxidation FeS2 + H2O + 7/2O2 Fe2+ + 2SO42- + 2H+ And FeS2 + 14Fe3+ + 8H2O  15Fe2+ + 8H2SO4 Later 4Fe2+ + O2 + 10H2O  4Fe(OH)3 + 8H+

41. Natural Organic Matter (Humic Matter) • Fulvic Acids (Fa): small fractions soluble in aqueous solution • Humic Acids (Ha): larger fractions soluble in alkaline sol. • Humin (Hu ): larger insoluble fractions

42. Delayed lake recovery • Fluctuations in streamflow patterns (particularly drought incidence) has strong impact of re-acidification of lakes • Decrease in DOC concentrations (Al3+ + flocculation) • Deeper penetration of UVB (factor of 3 in some lakes)

43. Extra slides

44. Basic Chemistry Review Covalent bonds Bonds in such compounds are formed by the sharing of e- rather than by the complete transfer of e- from one atom to another. The e- in covalent compounds exist in molecular orbitals formed by overlapping of two atomic orbitals. Sometimes, sharing two e- is not enough…

45. C) Basic Chemistry Review Electronegativity When two different atoms are joined by a covalent bond, the bonding e- are not necessarily shared equally  Atoms have different abilities to attract e-

46. Carbonate system - Acids in the environment Dominant carbonate species are related to K1 and K2 - But Why? Remember: Ka = [H+][A- ]/[HA] log Ka = log [H+]+ log ([A- ]/[HA]) -log Ka = -log [H+]- log ([A- ]/[HA]) pKa = pH - log ([A- ]/[HA])  pK1 = pH - log ([HCO3- ]/[H2CO3])

47. Carbonate system - Acids in the environment pK1 = pH - log ([HCO3- ]/[H2CO3]) At pH = pK1 pK1 - pH = - log ([HCO3- ]/[H2CO3]) 0 = - log ([HCO3- ]/[H2CO3]) 0 = - log[HCO3- ] + log[H2CO3] log[HCO3- ] = log[H2CO3] [HCO3- ] = [H2CO3]

48. What is the acidity of natural rain?

49. What is the acidity of natural rain? CO2(aq) + H2O = H2CO3º (total CO2 + H2CO3) KCO2 = [H2CO3 º]/PCO2 = 10-1.47(1) First dissociation step for carbonic acid: K1 = [H+][HCO3- ]/[H2CO3] = 10-6.35 (2) So, by combining equation (1) and (2) [H+] [HCO3- ] = K1 KCO2PCO2 (where PCO2 = 360 ppmv)

50. What is the acidity of natural rain? [H+] [HCO3- ] = KCO2K1 PCO2 (where PCO2 = 360 ppmv) Solving this yields [H+]2 = 10-1.47 x 10-6.35 x 10-3.44 [H+]2 = 1x10-11.26 pH = ? [H+] = (1x10-11.26)1/2 [H+] = 10-5.63 pH = 5.63