The Group 14 Elements

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Chapter 14

• The Group 14 Elements

2
Group 14 Elements

• Carbon
• nonmetal
• Silicon and Germanium
• semimetals
• Tin and Lead
• weakly, electropositive metals

3
Group 14 Properties

• Ability to form network covalent bonding and to
  catenate

Carbon (graphite)
Dichlorodimethyltin(IV)
4
Group Trends

• Melting and boiling points

Element Melting Point (C) Boiling Point (C)
Carbon Sublimes at 4100 Sublimes at 4100
Silicon 1420 3280
Germanium 945 2850
Tin 232 2623
Lead 327 1751
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Oxidation States

• Multiple oxidation states are common
• 4 for all the elements
• covalent bonding
• CO2
• -4 for C, Si, and Ge
• covalent bonding
• CH4
• 2 for Sn and Pb
• ionic bonding
• PbF2

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Stability of Oxidation States

• Frost diagram

Most stable? Most reducing? Most oxidizing?
7
Carbon

• Three common allotropes
• Diamond
• Graphite
• Fullerenes and carbon nanotubes

8
Diamond

• Covalent network of tetrahedrally, arranged
  covalent bonds

9
Diamond History

• Graphite and diamond were thought to be two,
  different substances
• In 1814, Humphry Davy burned his wifes diamond
  to prove it was indeed carbon
• C(s) O2(g) ? CO2(g)

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Diamond

• Electrical insulator
• Very good thermal conductor
• High melting point
• 4000C

Regular diamond (cubic)
Lonsdaleite (hexagonal)
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Diamonds in Nature

• Found predominantly in Africa
• Zaire is the largest producer
• 29
• Russia
• 22
• South Africa is the largest in terms of
  gem-quality
• 17

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Diamonds in Nature

• Crater of Diamonds State Park
• Murfreesboro, Arkansas
• http//www.craterofdiamondsstatepark.com/

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Synthetic Diamonds

• Can make synthetic diamonds from graphite by
  adding heat (1600C) and pressure (5 GPa)

Tracy Hall GE
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Synthetic Diamonds

• Thin films of diamonds can be made at low
  temperatures

Diamond Jet Reactor
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Synthetic Diamonds

• New methods have become available to produce more
  gem-quality stones

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Diamond Uses

• Drill bits and saws
• Surgical knife coatings
• Computer chip coatings
• Jewlery

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Graphite

• Hexagonal layers of covalently bound carbon
• similar to benzene
• delocalized pi system

18
Graphite Layers

• Very weak interactions between the layers
• 335 pm interlayer distance
• van der Waals radius
  is 150 pm
• abab arrangment

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Graphite Properties

• Excellent conductor in two dimensions
• due to the electron delocalization
• Excellent lubricant
• sheets slide
• Absorber of gas

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Graphite Reactivity

• More thermodynamically stable than diamond
• More kinetically reactive than diamond
• Forms intercalation compounds

21
Graphite Sources

• Mining
• China
• Siberia
• North and South Korea

22
Graphite Production

• Acheson Process

2500C, 30 hours
23
Graphite Uses

• Lubricants
• Electrodes
• Lead pencils
• clay mixtures
• hard mixtures 2H
• soft mixtures HB

24
Fullerenes

• Carbon atoms arranged in a spherical or
  ellipsoidal structure
• five and six-membered rings

C70
C60, Buckminsterfullerene
25
Fullerenes

• Named after R. Buckminster Fuller

R. Buckminster Fuller (1895-1983)
Buckminster Fullers Dome 1967 Montréal Expo
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Discovery of Fullerenes

• David Huffman and Wolfgang Krätschmer
• 1982

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Discovery of Fullerenes

• Kroto, Curl, and Smalley

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Discovery of Fullerenes

• Kroto, Curl, and Smalley

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Fullerene Production

• Huffman and Krätschmer

30
Fullerene Properties

• very weak intermolecular forces
• sublime when heated
• soluble in most nonpolar solvents
• give bright colors in solution

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Fullerene Properties

• C60 crystal lattice (fcc)
• low density, 1.5 g/cm3
• non-conductors of electricity
• strong absorber of light

32
Fullerene Chemistry

• Interstitial
• superconductors

Rb3C603- superconductor
33
Fullerene Chemistry

• Metal encapsulation
• Li_at_C82
• He_at_C60

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Fullerene Chemistry

• Reaction with gases
• C60(s) 30F2(g) ? C60F60(s)

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Cluster Sizes

• Many different sizes

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Carbon Nanotubes

• Sumio Iijima
• 1991

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Nanotube Types

• Single-walled (SWNT)
• Multi-walled (MWNT)

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Nanotube Properties

• excellent conductor
• molecular storage

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Impure Carbon

• Amorphous carbon (coke)
• made by heating coal in an inert atmosphere
• mostly graphite with some hydrogen impurities

• used in iron production
• removes oxygen
• 5 x 108 tons per year

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Impure Carbon

• Carbon black
• fine, powdered carbon
• 3.65 x 109 tons annually

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Impure Carbon

• Activated carbon
• high surface area
• 103 m2/g
• removes impurities from organic reactions
• decolorizes chemicals

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Carbon Isotopes

• Three isotopes
• carbon-12 (98.89 )
• carbon-13 (1.11 )
• carbon-14 (0.0000001)
• radioactive
• t1/2 5.7 x 103 years

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14C Radioactive Dating
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Carbon Chemistry

• Two important properties
• catenation
• a bonding capacity greater than or equal to 2
• an ability of the element to bond to itself
• a kinetic inertness of the catenated compound
  toward or molecules and ions
• multiple bonding

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Catenation

• An ability of an element to bond with itself

Carbon bonds Bond energy (kJ/mol) Silicon bonds Bond energy (kJ/mol)
CC 346 SiSi 222
CO 358 SiO 452
46
Bond Energies

• Important in determining the reactivity and/or
  relative stabilities of products
• CH4(g) 4F2(g) ? CF4(g) 4HF(g)
• not
• CF4(g) 4HF(g) ? CH4(g) 4F2(g)

Bond Bond energy (kJ/mol) Bond Bond energy (kJ/mol)
CH 411 CF 485
FF 155 HF 565
47
Carbides

• Binary compounds of carbon with more
  electropositive elements
• typically hard with high melting points
• three types
• ionic
• covalent
• metallic

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Ionic Carbides

• Formed by the most electropositive elements
• alkali and alkaline earth metals
• aluminum
• Only reactive carbides
• Na2C2(s) 2H2O(l) ? 2NaOH(aq) C2H2(g)
• Al4C3(s) 12H2O(l) ? 4Al(OH)3(s) 3CH4(g)

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Covalent Carbides

• Few examples
• silicon carbide and boron carbide
• only important nonoxide ceramic
• 7 x 105 tons produced annually

SiO2(s) 3C(s) ? SiC(s) 2CO(g)
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Covalent Carbides

• Silicon carbide uses
• grinding and polishing agents
• high-temperature materials applications
• mirror backings
• body armor

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Moissanite

• SiC
• hexagonal
• similar to lonsdaelite and ZrO2

SiC
Hardness (Mohs scale) Refractive index Density (g/cm3)
C 10 2.24 3.5
SiC 9.25-9.5 2.65-2.69 3.2
ZrO2 8.5 2.15 5.8
C
ZrO2
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Metallic Carbides

• Formed with transition metals
• carbon atoms fit in the octahedral interstices in
  the metal lattice (interstitial carbides)
• close-packed structure
• 130 pm metallic radius
• shiny luster
• conduct electricity
• hard and high melting point
• chemical resistance

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Metallic Carbides

• Tungsten carbide
• 20,000 tons produced annually
• used in cutting tools

54
Metallic Carbides

• Fe3C
• cementite

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Carbon Monoxide

• Colorless, odorless gas
• Very poisonous
• 300-fold greater affinity for hemeglobin than
  oxygen

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Carbon Monoxide

• Carboncarbon triple bond
• 1070 kJ/mol
• 1.11 Å bond length

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Carbon Monoxide Production

• Incomplete combustion
• CH4(g) 2O2(g) ? CO2(g) 2H2O(l)
• CH4(g) 3/2O2(g) ? CO(g) 2H2O(l)
• Dehydration of formic acid
• HCOOH(l) H2SO4(l) ? H2O(l) CO(g) H2SO4(aq)

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Carbon Monoxide Reactivity

• With oxygen
• 2CO(g) O2(g) ? 2CO2(g)
• With halogens
• CO(g) Cl2(g) ? COCl2(g)

phosgene
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Phosgene

• blister agent

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Carbon Monoxide Reactivity

• With sulfur
• CO(g) S(s) ? COS(g)
• As a reducing agent
• Fe2O3(s) 3CO(g) ? 2Fe(l) 3CO2(g)

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Carbon Monoxide Reactivity

• With hydrogen
• CO(g) 2H2(g) ? CH3OH(g)
• OXO process
• CO(g) C2H4(g) H2(g) ? C2H5CHO(g)
• 10 million tons of chemicals synthesized using a
  similar process

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Carbon Monoxide Reactivity

• With transition metals
• highly toxic
• used for preparation of other transition metal
  complexes
• Mo(s) 6CO(g) ? Mo(CO)6(s)

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Carbon Dioxide

• Dense, colorless, odorless gas
• low reactivity
• will not combust
• 2Ca(s) CO2(g) ? 2CaO(s) C(s)

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Carbon Dioxide

• No liquid phase at atmospheric pressure
• sublimes

Water
Carbon Dioxide
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Carbon Dioxide Use

• 40 million tons in the U.S. annually
• 50 in refrigerant applications
• 25 in the soft drink industry
• 25 in the aerosol, life raft, and
  fire-extinguishing industries

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Carbon Dioxide Sources

• Byproduct of manufacturing processes
• ammonia, molten metals, cement, sugar
  fermentation
• Reaction of an acid with a carbonate
• 2HCl(aq) CaCO3(s) ? CaCl2(aq) H2O(l) CO2(g)

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Carbon Dioxide Testing

• Limewater test
• CO2(g) Ca(OH)2(aq) ? CaCO3(s) H2O(l)
• CO2(g) CaCO3(s) H2O(l) ? Ca2(aq) 2HCO3-(aq)

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Carbonic Acid

• Used to carbonate soft drinks
• H2CO3(aq) H2O(l) ? H3O(aq) HCO3-(aq)
• HCO3-(aq) H2O(l) ? H3O(aq) CO32-(aq)

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Carbon Dioxide Reactivity

• With bases
• 2KOH(aq) CO2(g) ? K2CO3(aq) H2O(l)
• K2CO3(aq) CO2(g) H2O(l) ? 2KHCO3(aq)

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Introduction

• A supercritical fluid (SCF) is any substance at a
  temperature and pressure above its critical
  values
• Critical temperature of a compound is defined as
  the temperature above which a pure, gaseous
  component cannot be liquefied regardless of the
  pressure applied.
• Critical pressure is defined as the vapor
  pressure of the gas at the critical temperature.

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Introduction

• The temperature and pressure at which the gas and
  liquid phases become identical is the critical
  point.
• In the supercritical environment only one phase
  exists.
• The fluid, as it is termed, is neither a gas nor
  a liquid and is best described as intermediate to
  the two extremes.
• This phase retains the solvent power common to
  liquids as well as the transport properties
  common to gases.

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Table 1. Comparison of physical and transport
properties of gases, liquids and SCFs.  
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What does scCO2 look like?

• Here we can see the seperate phases of carbon
  dioxide. The meniscus is easily observed.

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What does scCO2 look like?

• With an increase in temperature the meniscus
  begins to diminish.

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What does scCO2 look like?

• Increasing the temperature further causes the gas
  and liquid densities to become more similar. The
  meniscus is less easily observed but still
  evident.

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What does scCO2 look like?

• Once the critical temperature and pressure have
  been reached the two distinct phases of liquid
  and gas are no longer visible. The meniscus can
  no longer be seen. One homogenous phase called
  the "supercritical fluid" phase occurs which
  shows properties of both liquids and gases.

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Extraction and Chromatography

• 1970s were first used commercially
• to decaffeinate coffee
• Media have been used successfully to extract
  analytes from a variety of complex compounds
  through manipulation of system pressure and
  temperature.
• By comparison, conventional methods (e.g.,
  Soxhlet extraction and vacuum isolation) are more
  complicated and time and energy intensive.

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Extraction and Chromatography

• The limiting property of sc-CO2 is that it is
  only capable of dissolving nonpolar organic-based
  solutes.
• The addition of small amounts of a cosolvent such
  as acetone has been shown to significantly
  improve the solubility of relatively polar
  solutes.

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Micelle Formation

• Solubility of ionic compounds such as aqueous
  metal salts has been enhanced through inverse
  micelle formation using fluorinated surfactants.

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Extraction

• SCF extraction has also been applied to
  environmental remediation such as removing
  organics from water and soil.
• To extract metal contaminants, a chelating agent
  is commonly added to the fluid, with the soluble
  metal complex being removed from the SCF
  following system depressurization.

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Other Uses for scCO2

• Catalysis
• Materials synthesis
• Chemical vapor deposition (CVD)

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The Greenhouse Effect

• Radiation trapping

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Molecular Vibrations

• Only heteronuclear, polyatomic molecules absorb
  infrared energy
• dinitrogen, dioxygen, and argon do not

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Earths Infrared Spectrum
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Sources of Carbon Dioxide

• Volcanoes
• Burning of vegetation
• Burning of fossil fuels

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Carbon Dioxide Levels
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Kyoto Protocol

• Results of a meeting of 161 countries in 1998 on
  greenhouse emissions
• Aims
• reduce the emmissions of carbon dioxide, methane,
  dinitrogen oxide, hydrofluorocarbons,
  perfluorocarbons, and sulfur hexafluoride
• reduce emissions by 5 of those in 1990

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Kyoto Protocol

• Solutions to the problem
• place a greater dependence upon the generation of
  power from non-carbon-based fuels
• wind, water, and nuclear power
• use carbon resources in a more efficient manner
• hybrid-fuel passenger vehicles
• biodiesel fuels

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Kyoto Protocol

• Other solutions
• if an industrialized nation helps a devloping
  country reduce its emissions, then that
  industrialized country can count part of the
  benefits towards its own reduction goal
• emission-reduction credits are tradable like
  stocks
• removing greenhouse gases by increasing forestry
  can also be credited

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Kyoto Protocol

• Signed by all nations except the U.S.
• U.S. produces 25 of the worlds emissions

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Carbon Dioxide Sequestration

• Storage of emitted carbon dioxide
• increasing photosynthetic absorption
• planting trees
• iron enrichment in seawater
• developing chemical technology to convert carbon
  dioxide into useful products
• limited due to quantities produced and energy
  needed

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Carbon Dioxide Sequestration

• Storage of emitted carbon dioxide
• storing the gas in underground geological
  formations
• separating CO2 from methane in natural gas
• pumping CO2 into oceans

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Carbon Dioxide Sequestration

• Pumping into oceans
• will greatly decrease the pH of the oceans
• CO2(aq) H2O(l) ? H3O(aq) HCO3-(aq)
• CO2(aq) CO32-(aq) ? 2 HCO3-(aq)

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Hydrogen Carbonates

• Prepared by reaction of the carbonate with carbon
  dioxide and water
• CaCO3(s) CO2(aq) H2O(l) ? Ca(HCO3)2(aq)
• All hydrogen carbonates decompose to the
  carbonate upon heating
• Ca(HCO3)2(aq) ? CaCO3(s) CO2(aq) H2O(l)

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Hydrogen Carbonates

• Amphoteric
• HCO3-(aq) H(aq) ? CO2(g) H2O(l)
• HCO3-(aq) OH-(aq) ? CO32-(aq) H2O(l)

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Carbonates

• Basic in solution due to hydrolysis
• CO32-(aq) H2O(l) ? HCO3-(aq) OH-(aq)
• washing soda

102
Carbonates

• bonding

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Carbonates

• Molecular orbitals
• 1 total pi bond
• 1/3 per oxygen atom

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Carbonates

• Properties
• most insoluble
• except alkali metal and ammonium carbonates
• most decompose upon heating to give the oxide
• CaCO3(s) heat ? CaO(s) CO2(g)
• for weakly electropositive metals,
• Ag2CO3(s) heat ? Ag2O(s) CO2(g)
• Ag2O(s) heat ? 2Ag(s) 1/2O2(g)

105
Carbon Disulfide

• Sulfur analogue of carbon dioxide
• colorless, highly flammable, low-boiling
• sweet smell when pure, foul when not
• highly toxic
• CH4(g) 4S(l) heat ? CS2(g) 2H2S(g)
• used in the production of cellophane, rayon
  polymers, and carbon tetrachloride
• 1 million tons annually

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Carbonyl Sulfide

• SCO, or COS
• most abundant sulfur-containing gas in the
  atmosphere
• 5 x 106 tons
• low reactivity
• only sulfur-containing gas to penetrate the
  stratosphere

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Carbon Tetrahalides

• Carbon tetrahedrally bound to four halogen
  molecules
• properties are dependent upon the dispersion
  forces present
• CF4 is a colorless gas
• CCl4 is a dense, oily liquid
• CBr4 is a pale, yellow solid
• CI4 is a bright, red solid

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Carbon Tetrachloride

• good, nonpolar solvent
• very carcinogenic
• was used in fire extinguishers
• oxidized to form poisonous carbonyl chloride,
  COCl2
• greenhouse gas and ozone depleter

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Carbon Tetrachloride

• Production
• FeCl3 catalyzed reaction
• CS2(g) 3Cl2(g) ? CCl4(g) S2Cl2(l)
• CS2(g) 2S2Cl2(l) heat ? CCl4(g) 6S(s)
• reaction of methane with chlorine
• CH4(g) 4Cl2(g) ? CCl4(l) 4HCl(g)

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Carbon Tetrachloride

• Reactivity
• very inert
• CCl4(l) 3H2O(l) ? H2CO3(aq) 4HCl(g)
• ?G -380 kJ/mol
• SiCl4(l) 3H2O(l) ? H2SiO3(aq) 4HCl(g)
• ?G -289 kJ/mol

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Chlorofluorocarbons

• First prepared in 1928 by GM chemist Thomas
  Midgley, Jr.
• CCl2F2
• very good refrigerant
• completely unreactive
• nontoxic

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Chlorofluorocarbons

• Nomenclature
• The first digit represents the number of carbon
  atoms minus one
• The second digit represents the number of
  hydrogen atoms plus one
• The third digit represents the number of fluorine
  atoms
• Structural isomers are distinguished by a,b,
  etc

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Chlorofluorocarbons

• Nomenclature

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Chlorofluorocarbons

• Ozone depleters
• Cl O3 ? O2 ClO
• ClO ? Cl O
• Cl O3 ? O2 ClO
• ClO O ? Cl O2

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CFC Alternatives

• HFC-134a
• CF3CH2F
• costly to produce
• current equipment needs to be replaced
• greenhouse gas

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Methane

• CH4
• colorless, odorless gas
• only detectable by addition of impurities
• major source of thermal energy (natural gas)
• CH4(g) 2O2(g) ? CO2(g) 2H2O(g)
• fastest growing gas in the atmosphere
• cattle and sheep by-products

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Cyanides

• HCN
• toxic but useful
• over 1 million tons annually
• Almond-like odor
• liquid at room temperature due to hydrogen bonding

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HCN Production

• Degussa Process
• CH4(g) NH3(g) Pt ? HCN(g) 3H2(g)
• Andrussow Process
• 2CH4(g) 2NH3(g) 3O2(g) ? 2HCN(g) 6H2O(g)

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Andrussow Process
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Hydrogen Cyanide

• Acidic in water
• HCN(aq) H2O(l) ? H3O(aq) CN-(aq)
• Neutralization produces sodium cyanide
• HCN(aq) NaOH(aq) ? H2O (l) NaCN(aq)
• used in the extraction of gold and silver from
  ores

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Hydrogen Cyanide Uses

• 70 in polymer production
• Nylon
• Melamine
• Acrylic plastics
• 15 in NaCN production

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Hydrogen Cyanide History

• The Peoples Temple

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Hydrogen Cyanide Gas Chambers

• 2NaCN(aq) H2SO4(aq) ? Na2SO4(aq) 2HCN(g)