Chemistry - an illustrated guide to science (794128), страница 26
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They are the only knownallotrope of carbon that can bedissolved.●BuckminsterfullereneThis form of carbon is composed of 60carbon atoms bonded together in apolyhedral structure composed ofpentagons and hexagons. Themolecules are made when an electricarc is struck between graphiteelectrodes in an inert atmosphere.This method also produces smallamounts of other fullerenes that haveless symmetrical molecular structures,such as C70 .● Buckminsterfullerene was firstidentified in 1985 and named after thearchitect Richard Buckminster Fullerbecause of the resemblance of itsstructure to the geodesic dome.● The substance is a yellow crystallinesolid that is soluble in benzene, anorganic solvent.● It is possible to trap metal ions withinthe C60 sphere. Some of thesestructures are semiconductors.●NanotubesNanotubes, first identified in 1991, arelong thin cylinders of carbon closed ateither end with caps containingpentagonal rings.● Nanotubes have a very broad range ofelectronic, thermal, and structuralproperties that change depending onthe kind of nanotube (defined by itsdiameter, length, and twist).●© Diagram Visual Information Ltd.Nanotube150CHEMISTRY OF CARBONThe carbon cycleKey wordsatmospherecarboncarbon cyclechlorophyllglucoseabphotosynthesisrespirationThe carbon cycleCarbon is the fourth most abundantelement in the Universe.● The total amount of carbon on planetEarth is fixed.
The same carbon atomshave been used in countless othermolecules since Earth began. Thecarbon cycle is the complex set ofprocesses through which all carbonatoms rotate.● Carbon exists in Earth’s atm osphereprimarily as carbon dioxide.● All green plants contain chlorophyll, apigment that gives them theircharacteristic color. Duringphotosyn thesis, chlorophyll trapsenergy from sunlight and uses it toconvert carbon dioxide and water intoglu cose and oxygen.● Carbon is transferred from greenplants to animals when animals eatplants or other animals.● All animals and plants need energy todrive their various metabolicprocesses. This energy is provided byrespiration . During this process,glucose reacts with oxygen to formcarbon dioxide and water.
These wasteproducts are subsequently releasedinto the atmosphere. In essence,respiration is the opposite process tophotosynthesis.● When plants and animals die, theirbodies decompose. In the presence ofair, the carbon they contain becomescarbon dioxide, which is released intothe atmosphere.● When plants and animals decay in theabsence of air, carbon cannot beconverted into carbon dioxide.Instead, it remains and forms fossilfuels such as coal, crude oil, andnatural gas.● When fossil fuels are burned, thecarbon they contain becomes carbondioxide and is released into theatmosphere.© Diagram Visual Information Ltd.●RespirationPhotosynthesisglucose+ oxygen → carbon + water + energydioxidesunlightcarbon+ waterglucose+ oxygendioxidechlorophyllC6 H12O8(aq) + 60 2(g) → 6CO2(g) + 6H2O(I)6CO2(g) + 6H20 (I) → C6 H12O6(aq) + 6O2(g)cdegfabcdefgcarbon dioxide in the airsunlightplants take in carbon dioxide and give out oxygenanimals take in oxygen, eat plants and vegetables, and breath out CO2death and decaycarbon compounds (e.g., in oil and coal)burning fuel produces CO2151Laboratory preparationof carbon oxides1 Preparation of carbon dioxideCHEMISTRY OF CARBONKey wordscarbonatecarbon dioxidecarbon monoxidecCarbon oxides●dabThe most common forms of carbonoxides are carbon dioxide, which isinstrumental in the carbon cycle, andcarbon m on oxide, a colorless,odorless gas that is the result of theincomplete combustion of fuels.
Theycan be prepared in the laboratoryusing the following techniques.1 Carbon dioxide2 Preparation of dry carbon dioxide●eCarbon dioxide is formed when ametal carbon ate reacts with a diluteacid:metal carbonate + dilute acid ➞metal salt + carbon dioxide + water●When calcium carbonate (marblechips) reacts with dilute hydrochloricacid:CaCO3(s) + 2HCl(aq) ➞CaCl 2(aq) + CO2(g) + H2O(l)●3 Preparation of carbon monoxide2 Dry carbon dioxide●jgHOOC-COOH(l) ——————————➞CO2(g) + CO(g) + H2O(l)h●fghijconcentrated sulfuric acidethanedioic (oxalic) acid crystals and concentrated sulfuric acidheatconcentrated potassium hydroxide solutioncarbon monoxideCarbon monoxide is formed by thedehydration of ethanedioic (oxalic)acid using concentrated sulfuric acid:conc. sulfuric acidimarble chipsdilute hydrochloric acidcarbon dioxidewatercarbon dioxideCarbon dioxide can be dried bypassing it through concentratedsulfuric acid and collected bydownward delivery (upwarddisplacement) because it is denserthan air.3 Carbon monoxide●abcdeCarbon dioxide is not very soluble inwater, so it can be convenientlycollected over water.Acid residues and carbon dioxide areremoved by passing the gas through apotassium hydroxide solution.
Carbonmonoxide can be collected over waterbecause it is only slightly soluble.© Diagram Visual Information Ltd.ef152CHEMISTRY OF CARBONKey wordsfractionaldistillationhydrocarbonThe fractional distillationof crude oil1 Fractional distillation of crude oildeFractional distillationFraction al distillation is one ofseveral processes used to refine crudeoil. Refining converts crude oil into arange of useful products.● Crude oil is a complex mixture ofhydrocarbon s.
During fractionaldistillation, this mixture is separatedinto a series of fractions (components)on the basis of boiling point.● The crude oil is passed through afurnace, where it is heated to 400°Cand turns mostly into vapor. The gasespass into a distillation column withinwhich there is a gradation oftemperature. The column is hottest atthe bottom and coolest at the top.● Hydrocarbons with the highest boilingpoints are the first to condense at thebottom of the column, along with anyremaining liquid residue from thecrude oil. This fraction providesbitumen for use in road building.● Rising up the column, other fractionscondense out: first diesel oil, thenkerosene, and finally gasoline.
All ofthese fractions are used as fuels.● The hydrocarbons with the lowestboiling points remain as gases and riseto the top of the column. This fractionis used as a fuel in the refinery.● The hydrocarbon vapor moves up thecolumn through a series of bubblecaps. At each level, the hydrocarbonvapor passes through condensedhydrocarbon liquid. This helps toensure a good separation into thevarious fractions.© Diagram Visual Information Ltd.●cfgbha2 Crude oil composition (percent yields and uses of oil)i18%j11.5%kli21%j13%k20 %l46%ij21%15%18%52.5%kl21%43%Crude oil composition●Crude oil varies in composition,depending on where it was obtained.Fractional distillation of different crudeoils provides different proportions ofthe various fractions.Arabianheavyabcdefcrude oilheaterbubble caprefinery gasgasoline (110 °C)kerosine (180 °C)IranianheavyghijklArabianlightdiesel oil (260 °C)residue — bitumen tar (40 0 °C)gasoline and chemical feedstockkerosinegas oilfuel oil153Other refining processesCHEMISTRY OF CARBONKey words1 Other refining processesalkanealkenecatalytic crackingfractionaldistillationfractional distillationisomerizationpolymerizationreformingresidfining1 Other processes●reformingcatalyticcrackingpolymerizationresidfining2 Isomerization2 IsomerizationCH3—CH2—CH2—CH2—CH2—CH3CH3—CH2—CH2—CH—CH3●CH3pentane2-methylbutaneIsomerization changes the shape ofhydrocarbon molecules.
For example,pentane is converted into 2methlybutane.3 Reforming3 ReformingDehydration●CH3CH3CHCCH2CH2CHCHCH2CH2CHCH+CH23H2CHmethylcyclohexane4 Catalytic crackingmethylbenzeneCyclization●CH3CHCH3—CH2—CH2—CH2—CH2—CH2—CH3CH2CH2heptaneCH2CH2CH2methylcyclohexaneOctane ➞ propane and pent-1-eneCH3CH2CH2CH2CH2CH2CH2CH3 ➞ CH3CH2CH3 + CH3CH2CH2CH=CH2propanepent-1-ene5 PolymerizationTwo propene molecules combine to form hexeneCH3CH= CH2 + CH3CH=CH2 ➞ CH3CH2CH2CH2CH=CH2propenepropenehex-1-eneIn general, smaller hydrocarbonmolecules, such as those in gasoline,are in greater demand than largerones. Catalytic cracking redresses thisbalance by breaking (cracking) largealkane molecules into smaller alkan eand alken e molecules.5 Polymerization●4 Catalytic crackingoctaneReforming converts straight chainmolecules into branched molecules inorder to improve the efficiency ofgasoline.
One type of reaction involvesthe dehydration of saturatedcompounds to unsaturatedcompounds. Another involves thecyclization of hydrocarbons.Polymerization combines smallmolecules to form larger moleculesthat can be used to make variousproducts.Residfining●Resifining is the process used on theresidue fraction to convert it intousable products. It also removesimpurities that would damage thecatalyst used in catalytic cracking.© Diagram Visual Information Ltd.isomerizationOther refining processes are used tomodify the products of fraction aldistillation .
These includeisom erization , reform in g, catalyticcrackin g, polym erization , andresidfin in g.154CHEMISTRY OF CARBONKey wordsalkanealkenealkynebondcarboncatenationvan der Waalsforces1 Catenation●Carbon has the ability to form longchains of carbon atoms in itscompounds. This is called caten ation .2 Melting and boilingpointsForces of attraction, called van derWaals forces, exist between molecules.As molecular size increases, there ismore overlap between the molecules,and the intermolecular forces ofattraction increase.● In order to melt and to boil, the forcesof attraction between molecules mustbe overcome. The greater theseforces, the more energy is needed.This is reflected in a steady increase inmelting point and boiling point asmolecules increase in size.Carbon chains1 CatenationChain length238H HH H HH H H H H H H HH C C HH C C C HH C C C C C C C C HH HH H HH H H H H H H H2 Melting and boiling points of some chains3Chain length●3 Types of bondsA carbon atom may form one, two, orthree bon ds with another carbon atomin its compounds.
These bonds aredescribed as single bonds ( C–C),double bonds ( C=C), and triple bonds( C!C).● Alkan es contain only carbon–carbonsingle bonds.● Alken es contain a carbon–carbondouble bond.● Alkyn es contain a carbon–carbon triplebond.● Alkanes, alkenes, and alkynes are allhydrocarbons since they consist onlyof hydrogen and carbon atoms.16H H HH H H H H HH C C C HH C C C C C C HH H HC3H8H H H H H HC6 H14m.p./ °C–187–94b.p./ °C–4169287H HH C C HCCH HAlkanesSingle bondHHC CHHAlkenesCDouble bondH C C HAlkynesCCTriple bondC16 H34183 Types of bonds●© Diagram Visual Information Ltd.6C155Naming hydrocarbonsCHEMISTRY OF CARBON1 Chain length gives first part of nameChain lengthFirst part of nameKey wordsC1C2C3C4C5C6meth-eth-prop-but-pent-hex-alkanealkenealkynefunctional grouphydrocarbonNaming hydrocarbons●2 Functional group gives second part of nameAlkaneFunctional groupAlkeneAlkyneC CC C-ene-yneH1 Chain lengthC H●HSecond partof nameThe name of a hydrocarbon indicatesthe number of carbon atoms in themolecule and what sort ofcarbon–carbon bonds is present.-aneThe first part of name is determinedby the number of carbon atoms in themolecule.
The same prefixes are usedfor all groups of organic compounds.2 Functional groupThe second part of the name isdetermined by the type ofcarbon–carbon bonds present. Eachfu n ction al grou p has a unique suffix.● The position of the functional group ina carbon chain is identified bynumbering the carbon atoms in thecarbon chain.●3 Examples of organic compound namesMoleculeChain lengthHFunctional groupNameHH C H1meth-C H-anemethane3 Examples of compoundnamesThe first two examples in the diagramare alkan es.
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