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M11-P1 Materials from the Earth

M11-P1 Materials from the Earth

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M11-P1 Materials from the Earth

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  1. M11-P1 Materials from the Earth 6th International Junior Science Olympiad (IJSO) Dr. Yu-San Cheung Department of Chemistry The Chinese University of Hong Kong

  2. Natural Resources(天然資源) • Naturally occurring substances • Considered valuable in their relatively unmodified (natural) forms • Values: depending on the amount available and the demand • A commodity is generally considered a natural resource when the primary activities associated with it are extraction and purification, as opposed to creation. • Examples of natural resources: Air, water, and soil Biological resources - plants and animals Raw materials (like minerals) Space and land Energy (like wind, geothermal(地熱的), tidal(潮汐的), and solar energy)

  3. Renewable Resources(再生資源) • They can restock (renew) themselves, be used indefinitely if they are not over-harvested. • If consumed at a rate that exceeds their natural rate of replacement, the standing stock will diminish and eventually run out. • Examples of living renewable resources: • trees (forests and woodlands) and crops • fish and livestock • Examples of non-living renewable resources: • fresh water • fresh air • Flow renewable resources (or simply “flow resources”): renewable, but needing no regeneration or re-growth e.g., wind, tidal, and solar energy

  4. Non-renewable Resources (非再生資源) • A non-renewable resource is a natural resource that cannot be re-made, re-grown, or regenerated on a scale comparative to its consumption. • Fossil fuels, such as coal, petroleum, and natural gas are often considered non-renewable resources, as they do not naturally re-form at a rate that makes the way we use them sustainable.

  5. Natural Resources and Their Products • Forests: timber (for building houses, boats, decks, and furniture; and making paper) • Mines: metal products, fossil fuels, salts, jewelry, gravel (for building roads and concrete) • Aquaculture(水產養殖): fishes, shrimps, crabs, etc.

  6. Minerals and Their Chemical Components Exercise: Find out the major chemical content in various types of minerals “Periodic Chart.pdf” in

  7. Common Minerals and Their Uses Exercise: Find out the uses of some common minerals.

  8. Cement & Concrete Cement: 水泥 Concrete:混凝土 Cement: • made from limestone, calcium, silicon, iron, and aluminum, plus lesser amounts of other ingredients • When water is added to cement, a chemical process occurs as it dries, allowing it to harden. Concrete: • cement + aggregates (e.g., sand, stone) • Important and widely-used construction material • Strengthened by steel-rod skeleton • Annual production: about 6 billion tons • (~1 ton each person on the Earth) • Life: 50,000 years

  9. Recycling(循環) Recycling is the reprocessing of materials into new products. It can save energy and reduce air pollution. Exercise: Find out the environmental effects of recycling.

  10. Recycling (循環) • Aggregates and concrete Crushed and used as aggregates for new concrete • Batteries Difficulty: so many types of batteries Some old types contain mercury and cadmium Lead-acid battery (mostly used in automobiles): containing lead • Biodegradable waste • Electronics waste(recovering metals) • Various types of metals(e.g., _________________________________) • Paper • Glass • Plastic • Rubber • Textiles • Timber

  11. + + + + +      Metals In chemistry: • A metal is an element that readily loses electrons to form positive ions (cations) and the cations are surrounded by a sea of electrons • Most metals form ionic bonds with non-metals [but not always, e.g., in Pb(C2H5)4, there is Pb–CH2CH3 covalent bond] Physical properties: • Electrical conducting • Some hard, some soft, some being liquid

  12. Alloys(合金) • Alloy: a homogeneous mixture of two or more elements, at least one of the elements is a metal, the resulting mixture has metallic properties. • An alloy usually has properties (physical and chemical) different from those of its components. Example The major component of steel is iron and steel is stronger than iron. If chromium is added, we have stainless steel which can resist corrosion.

  13. Examples of Alloys • Carbon steel: iron + carbon (higher carbon content, stronger but more brittle) - Low carbon steel: ~0.05 – 0.3% carbon content - Ultra-high carbon steel : ~1 – 2% carbon content • Stainless steel: steel + chromium (> 10%) • Brass: copper + zinc (typically ~30 – 35%) • Bronze: copper + tin (typically 12%) • Rose gold: gold + copper: for jewelry 24k: 100% gold (18k: 75% gold) (k = “karat”) • Solder: Conventional: Sn60/Pb40 (60% tin + 40% lead) Lead-free: e.g., SnAgCu (tin + silver + copper); different SnAgCu compositions: different melting points

  14. Energy Resources • Solar energy • Wind energy • Water-related: hydro power pumped-storage tidal power wave power • Geothermal energy • Biomass energy • Garbage energy • Nuclear energy • Fossil fuels

  15. Generation of Electrical Energy(電能) • Electrical energy is easily transported (from power plants to individual customers) • Electrical energy is versatile • Majority of energy available from Nature: in the form of kinetic energy and heat energy • Kinetic energy  electrical energy • Heat energy  kinetic energy of steam  kinetic energy of magnet/metal  electrical energy

  16. Lenz’s Law(楞次定律)Faraday‘s Law(法拉第定律) of Induction • In effect: Changing magnetic field  electrical current /Hbase/electric/farlaw.html • That is, kinetic energy  electrical energy

  17. Turbine(渦輪機) • Flow of fluid (acting on blazes)  rotation of shaft • Kinetic energy of fluid  kinetic energy of shaft electrical energy

  18. Solar Energy(太陽能) • Energy from the Sun • The Sun is a nuclear reactor, 150 million km away. Only a small fraction of light energy and heat energy (1 part in 1010) reaches the Earth, but it is a huge amount to the Earth. Ultra-violet(UV) Visible Infra-red (IR) • Solar cell: light energy  electrical energy • Water-heating system: heat energy  heat energy of water • Solar furnaces: heat energy  heat energy of gas  kinetic energy of gas  electrical energy Increasing wavelength “light” Absorbed and becoming heat energy

  19. Exercise: How is solar energy used for heating water in Hong Kong? Example:

  20. Wind Energy(風能) • Energy from wind • Ancient application: sailing • Used since Middle Ages: windmill • Electricity generation: wind  turbine  electricity (reverse of electric fan operation) Propeller blades Gearbox & generator in housing which can be rotated to face the wind Wind Tower

  21. Hydro Power(水力) • Energy from the flow of water: (potential energy of water  kinetic energy of water  …) • Ancient application: corn grinding, sailing, war • Used nowadays to generate 20% of the world’s electricity Dam Reservoir Turbine Generator

  22. Pumped Storage Reservoirs • They are not facilities or methods to generate electrical power. They are a way of storing energy so that it can be released quickly when needed. • Demand for electrical power changes throughout the day. When the demand is low, extra power not used is wasted. • A facility is needed which can store excess energy produced, and can release the stored energy immediately. Pumped storage reservoirs can do the job. Turbines & Pumps Lower Reservoir Top Reservoir

  23. Tidal Power(潮汐能) • Tide: water movement, containing kinetic energy • Twice a day • 8 sites in Britain, generating 20% of energy needed • ~20 potential sites in the world • Largest one: northern France Tide coming in Tide going out

  24. Off-shore Station

  25. Wave Power • Wave: generated by wind on sea surface • Method: reverse of a swimming pool wave machine Air flowing in and out Water level going up and down

  26. Geothermal Energy(地熱能) • The centre of the Earth: ~6000 C hot enough to melt rock • A few km down the surface: > 250 C • Used for thousands of years in some countries for cooking and heating Power station • If hot enough to produce steam  electricity • If not: heating Cold water down Hot water down Hot region

  27. Biomass(生物量) • Energy from organisms (usually plants) • Example: burning of wood for heat and light • Extraction of fuel: ethanol by fermentation: corns / canes  cane sugar  ethanol • Biodiesel: a fuel made from vegetable oil that runs in any unmodified diesel engine. Triglycerides (三酸甘油酯) (Esters of glycerol with long-chain fatty acids)

  28. NaOH + CH3OH Glycerol Glycerol part Fatty acid portions Methyl esters of fatty acid (Biodiesel) Triglycerides  Biodiesel

  29. Biodiesel Recipe: Biodiesel from New Oil Use of Biodiesel in automobiles Example: 1994 Dodge: 100,000 miles on 100% Rapeseed (芥花籽)

  30. Garbage Energy • Burning garbage: generating heat energy, but serious pollution (e.g., dioxin) • Bacterial action: generating landfill gas (mainly methane, CH4)

  31. Basis of Nuclear Physics & Nuclear Power

  32. Testing your knowledge on: molecules, atoms, and subatomic particles • A molecule consists of two or more _____ of the same or different elements. Examples: ____________________________ • Atoms are the smallest particles of an element. • Sub-atomic particles: particles that constitute atoms. ___________ ___________ ___________ Which of these sub-atomic particles make up nuclei?

  33. Testing your knowledge on: molecules, atoms, and subatomic particles Compare the sizes of: molecules, atoms, and nuclei. Exercise (fill-in-the-blank): Isotopes are atoms of the same _______ but having different numbers of ________ in their ________.

  34. 2 H 1 12 C 6 1 H 1 13 C 6 Nuclides(核素) A nuclear species characterized by specific values of theatomic number (no. of protons) and themass number (no. of protons and neutrons) element symbol mass number atomic number

  35. Radioactive(放射性)Substances Nuclei of some atoms, e.g., 40K, are unstable. They undergo spontaneous transformation into more stable atoms. The substance is called radioactive. Such a transformation process is called radioactivedecay. It is usually accompanied by emitting particles and energy collectively called radiation.

  36. Radioactivity(放射現象) The phenomena of radioactivity was discovered in 1896. This radiation was later shown to be separable by electric (or magnetic) fields into three types: alpha (a), beta (b) and gamma (g) rays. Electric plate (positive) • ray Radioactive material +  ray –  ray Lead block Luminescent screen Electric plate (negative)

  37. Stability of Nuclides(核穩定性) • Unstable nuclei are radioactive • Nuclei consist of proton(s) & neutron(s) • (except __________) • Forces inside the nuclei: • (1) Repulsive Coulomb force: between protons • (2) Attractive nuclear force: between proton & proton, • neutron & neutron, proton & neutron • Stability depends on the balance of the two forces

  38. Radioactive Decay Products • Alpha particle (helium-4 nucleus, 4He2+) • Beta particle (electron) • Gamma ray / X-ray (electromagnetic radiation) • Neutron

  39. Interaction of Radiation with Cells • Ionization and atomic excitation causing molecular • rearrangement or formation of free radicals • Alteration of molecules leads to malfunction of • physiological processes which depend on the • chemical structure • Examples: • inhibition of cell division, denature of enzymes, mutation of • genetic materials

  40. Rate of Radioactive Decay • Half-life (t1/2): the time it takes for half of its original amount • to decay 1  ½ ¼  1/8  1/16 …. After n half-lives, 1/(2n) is left. For example, after 10 half-lives, 1/(210) = 1/1024 (about 0.1%) is left.

  41. Half-lives of Some Radionuclides Each radionuclide has a characteristic t1/2 Radionuclide 81Kr 38K 73Se 131I 60Co 137Cs 14C 129I 235U 40K Half-life 13 seconds 7.6 min 7.2 hr 8 days 5.3 yr 30 yr 5730 yr 17 million yr 703 million yr 1260 million yr

  42. Sources of Radiation Natural Radiation • cosmic rays • terrestrial radiation (including radon) • food & drinks (40K within body) Artificial Radiation • medical instruments • leakage/disposal • radioactive fallout (weapon testing) • consumer products, e.g., smoke detectors, “glow in • the dark” watches

  43. Ba n U 235 n n Kr Ba Ba n n U 235 U 235 n n n n n This neutron starts the chain reaction Kr Kr Ba n U 235 n n Kr Nuclear Fuel(核燃料) 235U + n  139Ba + 94Kr + 3n • Characteristics: • Bombarded by neutron • Chain reaction: • 1 neutron in, • 3 neutrons out. • But not every neutron can hit • an 235U nucleus. • The reaction may eventually stop.

  44. Enriched Nuclear Fuel(核燃料) • To make the chain reaction self-sustaining, • we need to use: • uranium enriched in 235U • super critical mass of the fuel • Natural uranium: 238U (99.3%) & 235U (0.7%) • Enriched: 2-3% in 235U (>85% for bomb) • Methods: centrifugation, diffusion, • and electromagnetic isotopic separation.

  45. Critical Mass(臨界質量) Critical mass: sphere of 600 kg for 15% 235U (~40 cm diameter) Higher 235U percentage: larger/smaller critical mass Neutron reflector: larger/smaller critical mass

  46. Containment Structure Steam Generator Steam Line Reactor Turbine Control Rods Generator Cooling Tower Cooling Water Condensor Pumps Neutron absorber (e.g., boron, cadmium) Nuclear Power Plant(核能發電廠)

  47. Other Nuclear Fuels Plutonium-239 & Uranium-233

  48. Nuclear Fusion(核聚變) Heavy nuclei favor fission. Light nuclei favor fusion. Examples of nuclear fusions: 2H + 3H  4He + n 2H + 2H  3He + n 2H + 2H  3H + p

  49. Human-made Nuclear Fusion In order for a nuclear fusion to occur, two nuclei must be brought close enough. But the repulsion between nuclei is huge. Nuclei must contain high enough energy. Human-made nuclear fusion: through nuclear fission in nuclear bomb

  50. Nuclear Fusion(核聚變) in Nuclear Power Plant • Nuclear fusion: more energy released than fission • But … • once started, nuclear fusion is out of controlled and cannot be stopped. • Nuclear fusion for power generation: to be developed. • Other advantages of fusions over fissions: • less hazardous products • source more available (natural abundance of 2H: 0.015%)