Transcript Midterm Exam Notice

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 Earth
Element
Symbol
Percentage
of Atoms
Percent 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
Uses
Mild
Medium
High
0.2
0.3-0.6
0.6-1.5
Wire, pipes, nuts, bolts
Beams and girders
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 process
1. Crush and mix with caustic soda (NaOH),
solution crystallizes out aluminum hydroxide called
alumina
2. 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 nonreturnable 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
2O
+ 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
Cl. + O3
ClO. + O3
CF2Cl. + Cl.
ClO. + O2
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