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Lecture 2

Lecture 2. The Air We Breathe 4/6/2005. Scientific Notation (add’l info: Appendix 2 in text). Number X 10 Power. (between 1 and 10) More technically: 1 < Number < 10. Any negative or positive integer … … 10 -3 = 0.001 10 -2 = 0.01 10 -1 = 0.1 10 0 = 1 10 1 = 10

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Lecture 2

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  1. Lecture 2 The Air We Breathe 4/6/2005

  2. Scientific Notation (add’l info: Appendix 2 in text) Number X 10Power (between 1 and 10) More technically: 1 < Number < 10 Any negative or positive integer … … 10-3 = 0.001 10-2 = 0.01 10-1 = 0.1 100 = 1 101 = 10 102 = 100 103 = 1000 104 = 10000 … … Greater than or equal to Less than

  3. Anything with a constant composition Variable assortment of atoms, molecules or both Chemical combination of 2 or more elements Cannot be broken down into anything else by chemical process

  4. Microscopic View of Matter Always a molecule Atom: Smallest unit of an element that can exist stably (always an element) Molecule: Combination of a fixed number of atoms in a certain spatial arrangement (can be element or compound)

  5. Composition of Air • Nitrogen (78%) N2 • • Oxygen (21%) O2 • • Other • Argon (0.9%) Ar • Carbon dioxide (0.0375%) CO2 • Water vapor (0 - 4%) H2O • Pollutants (natural and artificial) • – carbon monoxide CO • – sulfur dioxide SO2 • – nitrogen oxides NO • – hydrocarbons • – ozone O3

  6. Formulas (blue) - N (red) - O • Nitrogen (78%) N2 • • Oxygen (21%) O2 • • Other • Argon (0.9%) Ar • Carbon dioxide (0.0375%) CO2 • Water vapor (0 - 5%) H2O • Pollutants (natural and artificial) • – carbon monoxide CO • – sulfur dioxide SO2 • – nitrogen oxides NOx • – hydrocarbons ? • – ozone O3 (black) - C (grey) - H Green - S

  7. Formulas (naming 2-element compounds) More metallic Prefix for # of atoms + Less metallic + ide Sodium chlorine + ide =chloride Carbon di oxygen + ide = dioxide Note: Prefixes are often omitted when the compound is unambiguous

  8. Air as a Mixture Formula for a mixture: Indicate the components joined by +’s Air: N2 + O2 + Ar + other gases • Homogeneous (same combination) at small distance scales • Heterogeneous (different comb.) at large distance scales – Changes over regions (weather) – Downwind of a fire: less O2, more H2O and CO2 – City vs. country – Lightning in thunderstorms makes NO and NO2 from N2 and O2 – Pollutants (downwind of a factory, near the 405)

  9. Atmospheric pressure: how hard the atmosphere “pushes” on you The more air above you, the higher the pressure. The higher you go in the atmosphere the “thinner” (i.e. less dense) the air. Air is still 21% oxygen, there is just less air.

  10. Air Pollution Limits

  11. Combustion (burning of hydrocarbons) Where do the pollutants come from? Carbon monoxide comes from burning of carbon compounds with insufficient oxygen. Chemical reactions are shown by equations: CH4 + 2O2 CO2 + 2H2O 2CH4 + 3O2 2CO + 4H2O

  12. Balancing Chemical Equations: Rule 1 • The number and types (symbols) of all elements on both sides must be the same. CH4 + 2O2 CO2 + 2H2O 1 C on both sides, 4 H on both sides, 4 O on both sides Rule 2 • Once you have written down the reactants (things on the left) and products (things on the right) correctly, you can’t change them! You can only change the coefficients (numbers in front). O2 + H2 H2O O2 + 2H2 2H2O • If no coefficient is present, assume it’s 1 unbalanced balanced

  13. Carbon Monoxide Why is carbon monoxide a pollutant? • Molecule in the blood called hemoglobin • Hemoglobin (Hb) binds and transports oxygen from lungs to tissues for metabolism O2 + Hb Hb-O2 (binding, lungs) Hb-O2 Hb + O2 (release, tissues) • Carbon monoxide binds to hemoglobin thousands of times more strongly than oxygen does CO + Hb Hb-CO – No Hb available to bind oxygen, so tissues can’t burn food!

  14. What can be done to reduce carbon monoxide? • • Gasoline additives (oxygenates) to increase amount of oxygen, the higher oxygen levels cause carbon to burn to CO2 rather than CO • – MTBE • • Oxygen-containing compound • • Very strong smelling • • Possible carcinogen? • – Ethanol • • Very popular in Midwest • • Producing pure ethanol consumes more energy than it saves • • Catalytic converters: promote complete burning to CO2 • 2CO + O2 2CO2 • Also reduce nitrogen oxide emissions

  15. Other Pollutants Sulfur dioxide (SO2) • Comes from burning sulfur S + O2 SO2 • Present as an impurity in coal (0.2-2%) and oil • Causes serious lung irritation at 10ppm • Acid rain Nitrogen oxides (NOx) • NO, NO2, N2O4, N2O5, N2O • Lung irritant, acid rain, tropospheric ozone • Some comes from lightning (biological nitrogen) • More comes from hot car engines N2 + O2 2NO 2NO + O2 NO2 • Run engines at a lower temperature – More CO, unburned hydrocarbons • Catalytic converter, that just reverses equation above – Produces more SO2

  16. Homework problems due 4/15/05 Chemistry in Context -- Chapter 1: #9, 14, 17, 21, 30, 39 Pick up handout for Problem #14

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