Lecture 7

Chapters 11 and 12

Chemistry of Earth

Core – thought to contain largely iron with some nickel, essentially inaccessible

Mantle – mostly silicate, few useful materials that are not readily available on the crust

Crust – often called the lithosphere, One half of all atoms in this layer are oxygen, next most abundant is silicon, then hydrogen

Elemental Composition of the Outer Portion of the EarthElement Symbol Percentage

of AtomsPercent by

Mass

Oxygen O 53.3 49.5

Silicon Si 15.9 25.7

Hydrogen H 15.1 0.9

Aluminium Al 4.8 7.5

Sodium Na 1.8 2.6

Iron Fe 1.5 4.7

Calcium Ca 1.5 3.4

Magnesium Mg 1.4 1.9

Potassium K 1.0 2.4

All others -- 3.7 1.4

Lithosphere: Organic and Inorganic

• Composed mainly of silicate minerals, oxide minerals, carbonate minerals, and sulfide minerals

• Thousands of mineral compounds compose the inorganic portion of the lithosphere

• Organic portion of the lithosphere includes all living things, their waste, decomposition products and fossilized materials

Silicates

• Basic structure unit of the silicate is an SiO4 tetrahedron

• May exist singly or joined in a variety of ways

Silicate Examples

• Quartz – pure SiO2 , because each silicon

atom is surrounded by four oxygen , it still assumes a tetrahedral structure,– Pure quartz is colourless, however various

impurities produce amethyst (purple), citrine (yellow), rose quartz (pink) and smoky quartz (gray to black)

– Some of these quartz crystals are used gems

• Micas – composed of SiO4 arranged in two dimensional sheet like arrays

– Easily cleaved into thin transparent sheets, once used for glass panels in stoves and lanterns

Asbestos – generic term for fibrous silicates. Composed of a double chain of tetrahedrals.

---Excellent thermal insulator, widely used for heating ducts, furnaces, steam pipes, protective clothing for firefighters. No longer in use due to carcinogenic properties

Modified Silicates

• Ceramics – made from clay composed of aluminum silicate. Mixed with water the clay can be shaped. Firing leaves a hard, porous material.

• When porous is not desired, various salts are added to the surface and heated to form a glass like matrix.

• Particles partially melt and fuse together

• Glass –made by heating a mixture of sand (silicon dioxide), sodium carbonate, and limestone (calcium carbonate)

• Mixture melts to a homogeneous liquid, and cools becoming hard and transparent.

• Properties of glass result from an irregular arrangement in the 3-D structure of SiO4 tetrahedral.

• When glass is heated, the weaker bonds break first and the glass gradually softens

• Modifying the proportions of ingredients, or substituting oxides of different metals for limestone allow different types of glass to be made

Types of Glass

• Soda Glass – made from calcium silicate and sodium silicate, used to make windows and all flat glass

• Borosilicate Glass – contains boron oxide along with small amount of sodium oxide and aluminum oxide, capable of withstanding temperatures up to 800 degrees Celsius, used in cooking and lab-ware

• Fiber Glass – produced by dropping molten glass on to a rotating disc. The glass flies off the disc forming fibers. Used to make components for cars, airplanes, boats, etc.

Metals and Ores

• Copper - first metal to be separated by early smelting technologies, heating copper carbonate or copper sulfide to produce Cu metal– Unreactive with water, or dilute acids– Extensively used in alloys

• Bronze – alloy copper and tin• Brass – alloy of copper and zinc• Copper coinage – alloy of copper, tin and nickel• Silver coinage – alloy of copper and nickel

Purification of Iron

• Iron ore, coke, limestone added to blast furnace

• Limestone combines with silicate impurities and forms molten slag which floats on top of the molten iron

• Molten iron is drawn out the bottom.

• Product is called pig iron

• Can be easily cast into molds hence it is also called cast iron

Production of Steel • Cast iron is brittle and has many impurities, so most is

converted to steel • Wrought Iron is the purest form of commercial iron. It

is produced by heating impure iron with limestone. This increases purity to about 95.5% creating a strong, malleable and ductile form of iron

• Steel is produced by the “Basic Oxygen Process” in which pressurized oxygen and lime are added to molten iron. These reacts with impurities such as phosphorus, silicon, and excess carbon which are poured off as slag.

• Two types of steel: carbon steel, alloy steel

Alloy Steel – a mixture containing up to 50% of one or more

other metals • Stainless Steels contain chromium and nickel.

These metals make it harder and corrosion resistant • Tool Steels contain tungsten and manganese which

improve hardness and heat resistance. Used for rock drills, cutting edges etc.

• Silicon Steels are used in the construction of electrical equipment such as electric motors, generators, and transformers

Carbon Steels• Contain up to 1.5 % carbon and accounts for 90% of

steel production• Hardness of carbon steel increases with carbon content• Mild steel is malleable and ductile, useful when load

bearing is not a primary consideration

Type % Carbon UsesMild 0.2 Wire, pipes, nuts, bolts

Medium 0.3-0.6 Beams and girders

High 0.6-1.5 Drill bits, knives, hammers

Aluminum

• Most abundant metal on earth’s crust• Exist as tightly bound ions in nature, requiring a

great deal of energy to extract in a two step process1. Crush and mix with caustic soda (NaOH), solution crystallizes out aluminum hydroxide called alumina2. Electrolysis separates aluminum and oxygen

• Process requires huge amounts of energy, only economical if energy is cheap

Aluminum Properties

• light yet strong, strength to weight ratio is higher than any other commercial metals

• resists corrosion, when exposed to air, forms a thin film of aluminum oxide, providing protection from oxygen

• highly reflective, commonly used in roofing to insulate buildings

• Non-toxic, used in making food, and brewing equipment

Costs of Production

• Silicates, especially glass produce solid wastes that do not decompose over time. Only choice is recycling.

• Purification of ores leaves chemical pollutant behind (cyanide from processing of gold)

• All silicates, metals, and ores exist in finite amounts and will run out

• Some metals (copper, gold) can only be found in ores with very low percentage composition. Limits economic viability

The Three R’s

• Reduce – the best current method, involves lessening the amount of throw-away garbage being used

• Reuse – make items durable enough to withstand repeated use

• Recycle – requires energy, but saves materials from being lost

Reuse

• It takes 6300J of energy to make one non-returnable 500 ml bottle

• It takes 8300J to make one reusable bottle

• The returnable bottle is used 12.5 times on average before it is broken

• Equates to 660 J per bottle (10% of the energy used to make one non-returnable)

Recycle

• It takes 5% as much energy to recycle new aluminum cans from old ones, than it does to make them from aluminum ore

• Using a ton of scrap steel to make new iron and steel saves 1.5 tons of iron ore and 0.3 tons of coal. It also results in 74% savings in energy, an 86% reduction in air pollution, and a 76% reduction in water pollution

Earth’s Atmosphere

• Consists of a mixture of gases which lies within 30 km of earth’s surface

• Divided into layers, troposphere in which we live, stratosphere where ozone exists, mesosphere, and thermosphere

• Dry air by volume contains 78% nitrogen, 21% oxygen, and 1% argon

Nitrogen

• Important component of many organic chemicals• Exists as diatomic N2 which cannot be used by plants or

animals• Requires fixing, which can occur via certain types of

bacteria, industrially or lighting.• Bacteria convert N2 to nitrates• Lightning forces N2 to react with O2 forming NO and

NO2

• Industrially fixed in the manufacturing of fertilizers

Nitrogen Cycle

Oxygen Cycle

Pollution

• A chemical in the wrong place (i.e. ozone)• May be a result of an atmospheric inversion

– Normally air close to the ground is warmest, cooling with increases in altitude

– If cool air gets trapped beneath a blanket of warm air, condition is known as atmospheric inversion

– No vertical air movement, results in the trapping of pollutants in the cooler section near the ground

Industrial Smog

• Characterized by the presence of smoke, fog, sulfur dioxide, and particulate matter such as ash and soot

• Burning of coal causes the most industrial smog

Chemistry of Smog

• High grade coal is mainly carbon, with as much as 3% sulfur

• Carbon combines with oxygen to produce carbon dioxide and carbon monoxide

• Sulfur combines with oxygen to produce sulfur dioxide, a serious respiratory irritant

• Sulfur dioxide reacts further with oxygen to form sulfur trioxide and then with water to form sulfuric acid

Particulate Matter

• Industrial smog is characterized by high levels of particulate matter (PM), with the largest particle visible as smoke or dust

• PM consists mainly of unburned carbon (soot) and minerals found in coal that do not burn

• These minerals are carried aloft with the intense thermal updraft created by the fire. This fly ash blankets everything around and contributes to respiratory problems

Dealing With Industrial Smog

• Main goal of reducing industrial smog pollution involves removal of PM

1. Electrostatic Precipitator – induces electric charges on the particles which are attracted to oppositely charged plates and deposited

2. Wet Scrubber – removes PM by passing stack gases through water. The water is sprayed in a fine mist. The waste water must then be treated

• Sulfur must be removed prior to combustion

Photochemical Smog

• Unlike industrial smog which accompanies cold, damp air, photochemical smog usually occurs during warm dry sunny weather

• Main culprits are unburned hydrocarbons and nitrogen oxides from automobiles

Carbon Monoxide

• Produced when a hydrocarbon burns with insufficient oxygen

• Largest contribution comes from motor vehicles (cigarette smoke also has high levels)

• Nonirritating, colourless, odourless, tasteless gas which binds to hemoglobin preventing the proper transport of oxygen by the bloodstream

• Only a local problem, CO does not exist for a significant amount of time (more than a week)

Nitrogen Oxides

• Produced by automobile exhaust, and power plants burning fossil fuels

• Nitrogen combines with oxygen producing nitrogen dioxide, an amber coloured gas.

- NO2 absorbs a photon to break down into nitric oxide and a reactive oxygen atoms. Reactive oxygen combine with O2 forming ozone which reacts with hydrocarbons forming aldehydes

• Nitrogen oxides lead to smog formation. These gases also contribute to the fading and discolouration of fabrics, and acid rain.

Volatile Organic Compounds

• (VOC’s) sources include gasoline vapours, combustion products of fuels, and aerosols.

• Many VOC’s are hydrocarbons

• Hydrocarbons can pollute without burning

• Alkenes combine with oxygen to produce aldehydes, having foul irritating odours

Solutions to Photochemical Smog

• Principle culprits are nitrogen oxides, hydrocarbons, and sunlight, a reduction in any of these would reduce the smog

• Reduction of hydrocarbons requires industry to switch solvents, and/or modify existing systems

• Nitrogen oxides may be reduced by lowering the operating temperature of an engine

• Operating at a higher fuel to air mixture lowers the NO2 levels but raises carbon oxides

Ozone

• Form of oxygen consisting of O3

• Natural component in the stratosphere, shielding earth from life-destroying UV radiation

• Also a component of photochemical smog, inhaled it is toxic and dangerous

O2 + UV Radiation 2 O + 2 O2 2 O3

Degradation of the Ozone Layer

• Excess ozone in the troposphere and too little ozone in the stratosphere threaten our health

• Ozone layer has been thinning 0.5% /yr since 1978• Mainly as a result of CFC use• CFC have been used as dispersion agents, foaming

agents and refrigerants. At room temp they are gases or liquids, insoluble in water and inert towards most other substances

• Inertness allows these to persist in the environment

Impact of CFC’s

CF2Cl2 + UV light CF2Cl. + Cl.

Cl. + O3 ClO. + O2

ClO. + O3 O2 + Cl.

- occurs in the stratosphere, Cl. is recycled, allowing one molecule of CFC to degrade many molecules of ozone

Acid Rain

• Sulfur oxides convert to sulfuric acid• Nitrogen oxides convert to nitric acid• Acid rain is defined as rain with a pH of less than 5.6• Rain with pH of 2.1 has been reported• Acids corrode metals and stone buildings forming

salts and hydrogen gas• Salts are soluble in water, and wash away• Acid rain also has a dramatic impact on plant life,

altering the soil composition

Greenhouse Effect

• Carbon dioxide, methane, water, and CFC’s are all greenhouse gases

• Prevent heat from radiation into space