Bases = Anti-Acids. The process is called neutralization (neither acidic nor basic) O H 3 2H 2

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1 Bases = Anti-Acids Example: HCl(aq) + H 2 (l) à H 3 + (aq) + Cl - (aq) NaH(aq) à Na + (aq) + H - (aq) H 3 + (aq) + H - (aq) à 2H 2 (l) Net: HCl(aq) + NaH(aq) à Na + (aq) + Cl - (aq) + H 2 (l) The process is called neutralization (neither acidic nor basic) How much hydronium ion is in a neutral solution? [H 3 + ][H - ]=1x10-14 at 25 C 2H 2 H H Concentration in Molar (M) of hydronium ion times the concentration in Molar (M) of hydroxide ion is a constant in water solution. If [H 3 + ] goes up, [H - ] goes down; if [H - ] goes up [H 3 + ] goes down. In a neutral solution [H 3 + ] = [H - ] = 1x10-7 if [H 3 + ] > [H - ] acidic solution: if [H 3 + ]=1x10-4 then [H - ]=1x10-10 if [H 3 + ] < [H - ] basic solution: if [H 3 + ]=1x10-9 then [H - ]=1x10-5 acidic basic

2 [H3 + ]/[H - ]/ph/ph [H 3 + ] x [H - ] = 1 x (a constant) definition of ph: ph = -log[h 3 + ] H 3 + = 10 ph ph<7 acidic ph>7 basic ph=7 neutral [H 3 + ] > [H - ] [H 3 + ] < [H - ] [H 3 + ] = [H - ] ph = -log[h - ] ph+ph=14 If [H 3 + ] = 1 x 10-3 then [H - ] =??? 1 x acidic? yes If [H 3 + ] = 1 x 10-8 then [H - ] =??? 1 x 10-6 acidic? no If [H - ] = 1 x 10-5 then [H 3 + ] =??? 1 x 10-9 acidic? no If [H - ] = 1 x then [H 3 + ] =??? 1 x 10-4 acidic? yes If ph=5 then ph=??? 9 acidic? yes If ph=7 then ph=??? 7 acidic? no If ph=8 then ph=??? 6 acidic? no If ph=3 then ph=??? 11 acidic? no 27

3 ph of Common Substances lower ph à higher [H 3 + ] à more acidic [H 3 + ] Litmus paper ph indicator: red = acidic blue = basic

4 ph of Rain, Normal and therwise [H 3 + ] Rain condenses from water vapor in the atmosphere so atmospheric gases will be dissolved in the water: An equilibrium is established between carbon dioxide and water: C 2 + H 2 H 2 C 3 H C H H 2 C 2 + H 2 H HC 3-3 HC H 2 3 H C 3 2- this leads to a ph 5.6 solution

5 ph of US Rain (2005) expected ph: ~5.6 due to dissolved C 2 Where does extra acidity come from?

6 Sources of Extra Acidity Remember: S 2 is formed when coal is burned S 2 (g) + H 2 (l) à H 2 S 3 (aq) H 2 S 3 (aq) + H 2 (l) à H 3 + (aq) + HS 3- (aq) Sulfurous acid S 3 (g) + H 2 (l) à H 2 S 4 (aq) H 2 S 4 (aq) + H 2 (l) à H 3 + (aq) + HS 4- (aq) HS 4- (aq) + H 2 (l) à H 3 + (aq) + S 4 2- (aq) Sulfuric acid hydrogen sulfate ion sulfate ion Remember: N 2 formed when any combustion occurs (from N 2 in air) 4N 2 (g) + 2H 2 (l) + 2 (g) à 4HN 3 (aq) HN 3 (aq) + H 2 (l) à H 3 + (aq) + N 3- (aq) Nitric acid nitrate ion

7 Deposition of Nitrate and Sulfate Dry deposition solid (pollutant) particles dispersed in the atmosphere, eventually settle back to the ground Wet deposition solid particles dissolved in rain, return to the ground via precipitation Nitrate Sulfate Burning coal (Chapter 4): 2C 135 H 96 9 NS à 270C H 2 + 2N 2 + 2S 2 In atmosphere: 2S 2 (g) + 2 (g) à 2S 3 (g) S 4 2 and N 3 from coal combustion; N 3 also from automobile traffic

8 How Much S 2 is Produced? US consumption of coal: Smelting ore NiS + 2 à Ni + S 2 US emissions, x10 9 short tons 2.13x1010 J 1 short ton = 2.45x1019 J=24.5 EJ S 2 generation from coal combustion (assumes no mitigation): burning coal 1.15x10 9 short ton 2C 135 H 96 9 NS à 270C H 2 + 2N 2 + 2S 2 Molar mass: C 135 H 96 9 NS: 135x x1.0+9x = g/mol kg 1 short ton 1000 g 1 mole Coal 1 kg g Coal 1 mole S 2 1 mole Coal 64.1 g S 2 = 3.51x10 13 g S 2 1 mole S 2 = 3.9x10 7 short ton assumes no mitigation

9 Acid Rain, West Coast Style Very little S 2 in Los Angeles, nevertheless the rain can be very acidic... US Sources of N x (2003) In Unit 2.2: Nitrogen (N 2 ) not very reactive but is 78% of air and does react at high temperatures N N + N N à 2N 2N + 2 à 2N 2 slow in air but accelerated by VC (volatile organic compounds) & H VC + H à A A + 2 à A A + N à A + N 2 A, A, and A produced from oxidation of VC N 2 (g) + H (g) à HN 3 (g) HN 3 (g) + H 2 (l) à H 3 + (aq) + N 3- (aq)

10 US Emissions of S x and N x Emissions in millions of short tons More difficult to estimate emissions of N x than S x (less centralized emission points for the former) Note: for S 2, we estimated 39 million short tons (?) 1970s: catalytic converters introduced (S removed from gasoline) 1990: Clean air act amendments

11 in billions of kg Note we estimated 35x10 9 kg for US without emission controls

12 Impacts of Acid Rain 4Fe(s) + 22(g) + 8H3+(aq) à 4Fe2+(aq) + 12H2(l) 4Fe2+(aq) + 2(g) + 12H2(l) à 2Fe23(s) + 8H3+(aq) Net: 4Fe(s) + 32(g) à 2Fe23(s) rust acid is catalytic

13 Impacts of Acid Rain CaC 3 (s) + 2H 3 + (aq) à Ca 2+ (aq) + C 2 (g) + 3H 2 (l) Marble contains both magnesium carbonate and calcium carbonate

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15 Environmental/Biological Effects of Acidification R Remember: triglyceride H 2 C R CH CH 2 R + 3 CH 3 H Lye or Catalyst H CH H 2 C CH 2 H H + 3 R CH 3 C H N R C C N C C H N H R H 3 + or H - + H 2 N C C C H H + N C C H N R H protein R H

16 S x and N x Reduction via Clean Coal Technology CCT: clean coal technology Fig. 6.28

17 Review 42

18 Summary Composition of the atmosphere is pretty vital to life Components are mostly pretty simple gases in ppt-pph concentrations N 2, 2, Ar, C 2 Pollutants are found in ppb-ppm concentrations criteria (regulated) pollutants: C, N 2, 3, S 2, Pb, PM x C 2 is not a pollutant direct (out of the tailpipe ) versus indirect pollutants Knowledge of chemical nomenclature important forms of matter (especially compounds vs mixtures) prefixes for naming compounds (N 2 is not the same thing as N 2!) Balancing chemical reactions leads to insight on fighting pollution e.g. complete vs incomplete combustion e.g. catalytic conversion of C to C 2 Pollutants can be reduced, but never removed entirely balancing the costs against the benefits (e.g. are we really going to give up all of our cars? can we?) need to assess the risk involved in our behaviors

19 Unit 2.3 Summary Concepts definitions of acids and bases acids produce hydronium when dissolved in aqueous solutions bases produce hydroxide when dissolved in aqueous solutions acid-base equilibria and neutralization acid + base à salt + water [H 3 + ] * [H - ] = 1 x (a constant) definition of ph ph = -log[h 3 + ] nitrogen cycle Questions to organize your thoughts: Which substances are acidic? Which are basic? How do we find out (measure)? How do acid-base equilibria work? What are the sources of extra acidity in rain? What are the biological and/or environmental consequences of acid rain? How does the nitrogen cycle work, how do people impact the amounts of nitrogencontaining compounds, and what are the consequences? What are the ways we might reduce sources of acid rain? 44

20 Bonding Recap Covalent bond equal sharing of electrons between two atoms example: N 2, :N N:, :N:::N: Polar covalent bond unequal sharing of electrons between two atoms element with the higher electronegativity (EN) holds the electron pair more closely example: H 2 covalent compound: atoms present in fixed proportions, bonding between atoms is of the (polar) covalent flavor Ionic bond electrostatic interaction between a cation (+) and an anion ( ) polyatomic ions: two or more ions are covalently bound together; that species carries a positive or negative charge ionic compound: ions are present in fixed proportions and arranged in a regular geometric pattern; ions break apart when dissolved Hydrogen bond intermolecular interaction between polar species partial positive charge on H; partial negative charge on other atom (N,, F)

21 Unit 2.2 Summary Concepts electronegativity è polar bonds è polar molecules (sometimes) hydrogen bonding: effects on melting and boiling points; effects on solubility ions and ionic compounds anions (-) cations (+) polyatomic ions concentration terms ppm = mg solute /L H 2 ppb = µg solute /L H 2 molarity (M) = mol solute/l solution Questions to organize your thoughts: What makes water an unusual compound? What is our water used for? How is our drinking water purified? What are safe levels of minerals and/or contaminants? 46