Chemistry - an illustrated guide to science (794128), страница 19
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Thenail is exposed to water but notoxygen and does not ru st.● Tube B: Anhydrous calcium chlorideremoves moisture from the air. Thenail is exposed to oxygen but notwater and does not rust.● Tube C: The nail is exposed to bothwater and oxygen, and rust formson it.2 Chemical process● Ironatoms are oxidized to form firstiron(II) ions, Fe2+ , and then iron(III)ions, Fe3+ , present in rust, Fe2O3.xH2O.● Oxygen is reduced and combined withwater to form hydroxide ion s, OH- .3 Rust preventionmagnesium blocksmethods of rust preventioninvolve stopping iron or, morecommonly, steel from coming intocontact with water and/or oxygen inair. These methods include painting,greasing, coating in plastic, coating inzinc (galvan izin g), and coating in tin.● Sacrificial protection involves boltingblocks of a more reactive metal, suchas m agn esiu m , to a steel structure.The magnesium will oxidize morereadily than the iron and will thus“sacrifice itself” in order to preventiron from rusting.© Diagram Visual Information Ltd.● Most110PATTERNS—METALSKey wordsanodecathodeelectrolyteslagCopper smelting andconverting1 Matte smelting1 Matte smeltingsmelting is used to produce aliquid sulfide phase (matte) containingas much copper as possible, and animmiscible liquid slag, which containsvirtually no copper.● Copper sulfide ores, such aschalcopyrite ( CuFeS2) are mixed withsand and blown into the flash furnace:gas exit● Mattesand and oreconcentratesand and oreconcentrate4CuFeS2(s) + 5O2(g) + 2SiO2(s) ➞2Cu2S.FeS(l) + 2FeSiO3(l) + 4SO2(g)matteslag● Asthe iron content of the matte fallsto about 1 percent, copper starts toform.
This product is called “blistercopper” and is 98–99.5 percent pure.It is porous and brittle and requiresfurther refining to be commerciallyuseful.● Blister copper is melted to drive offsulfur dioxide, and air is blownthrough it to remove any sulfur.
Theimpure copper is cast into an odes forelectro-refining.oxygenoxygenslagslag2 Electro-refining2 Electro-refining● Inelectro-refining, a large impurecopper anode and a small pure coppercathode are suspended in anelectrolyte consisting of copper(II)sulfate solution and sulfuric acid.● At the anode, copper atoms areoxidized to copper ions and pass intosolution.
The anode graduallybecomes smaller:+–anodecathodesolution ofcopper (II)sulfate andsulfuric acidCu(s) ➞ Cu2+ (aq) + 2e● At© Diagram Visual Information Ltd.the cathode, copper ions areremoved from solution as they arereduced to copper atoms. The cathodegradually becomes larger:mattematteimpurecopperanodepurecoppercathodeCu2+ (aq) + 2e- ➞ Cu(s)● Impuritiesthat are insoluble in theelectrolyte fall to the bottom of thecell. These may include gold, silver,platinum, and tin, and in somecircumstances may be more valuablethan the copper produced.impurities (including gold,silver, platinum, and tin)111Reactions of copperPATTERNS—METALSKey wordsCu2+doubly ionized copperDilute acidshydrochloric acidnitric acidoxidation stateoxidizing agentsulfuric acidtransition metalsReactions of copper● CopperConcentrated nitricor sulfuric acidDissolvedH+ (aq)CuOCuHeat in airat 800°CCu2 Oblack copperred, insolubleHeat in airoxidecopper oxideabove 1,000°Cis a tran sition m etal.
Itsnormal oxidation state is copper(II),Cu2+ , but it also forms some copper(I),Cu+ , compounds. Copper is a relativelyunreactive metal. It does not reactwith dilute strong acids, water, orsteam.● When heated in air at 800°C, copper isoxidized to black copper(II) oxide:2Cu(s) + O2(g) ➞ 2CuO(s)At temperatures over 1,000°C, redcopper(I) oxide is formed:4Cu(s) + O2(g) ➞ 2Cu2O(s)Both oxides react with dilute acids toform copper(II) salts.● When heated in chlorine, copperforms brown copper(II) chloride.ConcentratedhydrochloricacidAir(slowtarnishing)Cu(s) + Cl 2(g) ➞ CuCl 2(s)● Whitecopper(I) chloride also existsand can be made by strongly heatingcopper(II) chloride:DilutestrongacidsCuCO3.Cu(OH) 2green patinaHeatin drychlorineno reactionCuCl2brown copper chlorideCuClwhite,insolublecopperchlorideIt is also formed by the reaction ofcopper(II) oxide with concentratedhydrochloric acid via an complex ion,[ CuCl 2] - .
When a solution containingthis ion is poured into water,copper(I) chloride is precipitated.● Copper tarnishes slowly in air, formingbasic copper(II) carbonate, acompound of copper(II) carbonate,and copper(II) hydroxide,CuCO3.Cu(OH) 2. It is this compoundthat produces the green coloration,referred to as patina, on weatheredcopper.● Copper reacts with both concentratednitric and concentrated su lfu ric acid.Both of these concentrated acids arepowerful oxidizin g agen ts and reactwith copper in a different way than adilute acid reacts with a metal.
Copperdoes not react with dilute acids.With concentrated sulfuric acid:Cu(s) + 2H2SO4 (l) ➞CuSO4 (aq) + 2H2O(l) + SO2(g)With concentrated n itric acid:Cu(s) + 4HNO3 ➞Cu(NO3) 2(aq) + 2H2O(l) + 2NO2(g)© Diagram Visual Information Ltd.2CuCl 2(s) ➞ 2CuCl(s) + Cl 2(g)112PATTERNS—METALSKey wordsaluminumamphotericcarbonatecopperhydroxideironoxidation stateoxidetransition metalsvalencyReaction summary:aluminum, iron, andcopperAluminumReactivity● Alu m in u mis the most reactive andcopper is least reactive of the threemetals.● All three metals react directly withnon-metals.Oxideshas one oxide, Al 2O3, whichis am photeric and thus reacts withboth acids and alkalis.
Iron has threeoxides: FeO, Fe2O3, and Fe3O4 . Copperhas two: Cu2O and CuO. All metaloxides react with dilute acids to formsalts and water.PreparationElectrolysis of aluminum oxideAl 3+ + 3e– → Al at cathodeReaction of elements4Al + 3O2 → 2Al 2 O3 oxide layer formed2Al + 3Cl 2 → Al 2 Cl 62Al + 3H2SO4 → Al 2 (SO4 ) 3 + 3H2OxideAl 2O3 + 3H2SO4 → Al 2(SO4 ) 3 + 3H2OAl 2O3(s) + 2NaOH(aq) → Na[Al(OH) 4 ] (aq)HydroxideAlCl 3 + 3NaOH → Al(OH) 3 + 3NaClAl(OH) 3 + 3HCl → AlCl 3 + 3H2 OAl(OH) 3(s) + NaOH(aq) → 2Na[Al(OH) 4 ] (aq) (amphoteric)● AluminumCarbonateNot formedChange of valencyOnly on oxidationIronPreparationChemical reduction in blast furnaceFe2O3 + 3CO → 2Fe + 3CO2Reaction of elements2Fe + 2H2O + O2 → 2Fe(OH) 2 rustFe + 2HCl → FeCl 2 + H2Hydroxides● Aluminumhydroxide, like aluminumoxide, is amphoteric.
Iron forms twohydroxides by the addition of sodiumhydroxide solution to solutions of itssalts. Iron(II) salts produce a dirtygreen precipitate of iron(II) hydroxide,while iron(III) salts produce a redbrown precipitate of iron(III)hydroxide. Copper(II) hydroxideforms as a blue precipitate whensodium hydroxide is added to asolution of a copper salt.● All metal hydroxides react with alkalisto give metal salts and water.2Fe + 3Cl 2 → 2FeCl 3Fe + S → FeSFe + H2SO4 → FeSO4 + H2OxideFeO + H2SO4 → FeSO4 + H2OFe2O3 + 3H2SO4 → Fe2(SO4 ) 3 + 3H2OHydroxideFeCl 2 + 2NaOH → Fe(OH) 2 + 2NaClFeCl 3 + 3NaOH → Fe(OH) 3 + 3NaClFe(OH) 2 + 2HCl → FeCl 2 + 2H2OFe(OH) 3 + 3HCl → FeCl 3 + 3H2OCarbonateUnstable to heat.
FeCO3 → FeO + CO2FeCO3 + H2SO4 → FeSO4 + CO2 + H2OChange of valency3+–2Fe2+(aq) + Cl 2(g) → 2Fe (aq) + 2Cl (aq)Carbonates© Diagram Visual Information Ltd.● Aluminumand iron(III) do not formcarbon ates. Iron(II) carbonate andcopper(II) carbonate decompose onheating to the corresponding metaloxide with the loss of carbon dioxidegas. The carbonates also react withdilute acids to forms metal salts,carbon dioxide, and water.Valency● Aluminumis in group 3 of the periodictable and exhibits only one oxidationstate, + 3, in its compounds. Iron andcopper are both tran sition m etals andexhibit two oxidation states in theircompounds.CopperPreparationThermal decomposition in furnaceairCu2S → 2Cu + SO2Reaction of elements2Cu + O2 → 2CuOCu + Cl 2 → CuCl 22Cu + S → Cu2SCuCl 2 + H2SO4 → no reaction with dilute acidCu + 2H2SO4 → CuSO4 + SO2 + 2H2O with conc.
acidOxideCuO + H2 SO4 → CuSO4 + H2OHydroxideCuCl 2 + 2NaOH → Cu(OH) 2 + 2NaClCu(OH) 2 + 2HCl → CuCl 2 + 2H2OCarbonateUnstable to heat. CuCO3 → CuO + CO2CuCO3 + H2 SO4 → CuSO4 + CO2 + H2OChange of valency++––2Cu2+(aq) + 2l (aq) → 2Cu (aq) + l 2(s) then Cu (aq) + l (aq) → Cul (s)113The extraction of metalsfrom their oresMetal (Date of discovery)Ranked from highest tolowest in reactivity seriesMain ore from whichit is obtainedMain method ofextractionPATTERNS—METALSKey wordselectrolysisorereactivity seriesreductionExtraction of metals● TheSodium (1807)Rock saltElectrolysis ofGroup 1NaClmolten NaClMagnesium (1808)MagnesiteElectrolysis ofGroup 2MgCO3 and Mg2+molten MgCl 2ions in seawaterAluminum (1827)BauxiteElectrolysis of Al 2O3Group 3Al 2O3.2H2Oin molten cryolite(Na3AIF6 )Zinc (1746)Zinc blendeHeat sulfide in air ➞Transition metalZnSoxide.
Dissolve oxidein H2SO4 , electrolyzeIron (ancient)HematiteReduce Fe2O3 withTransition metalFe2O3carbon monoxideTin (ancient)TinstoneReduce SnO2 withGroup 4SnO2carbonLead (ancient)GalenaHeat sulfide in air ➞Group 4PbSoxide. Reduce oxideease with which a metal isobtained from its ore is directly relatedto its position in the reactivity seriesof metals.Electrolytic reduction● Allof the group 1 and group 2 metalsand aluminum from group 3 arereactive metals and in the upper halfof the reactivity series. They cannot beobtained from their ores by chemicalredu ction , i.e., by heating the ore witha reducing agent such as carbonmonoxide or carbon.
These metals canonly be obtained by electrolyticreduction or electrolysis.● Consequently, it was impossible toobtain these metals before thediscovery and development ofelectricity at the end of the eighteenthcentury. All of these metals were firstmade in the early years of thenineteenth century, several by Englishchemist Sir Humphrey Davy.Heatingwith carbonCopper (ancient)Copper pyritesControlled heatingTransition metalCuFeS2with correct amount(CuS + FeS)of air ➞ Cu + SO2Mercury (ancient)CinnabarHeat in air ➞Transition metalHgSHg + SO2oxide and iron oxide are reducedby heating with carbon monoxide.Although zinc can be obtained bychemical reduction, approximately 80percent of the world’s annualproduction is, in fact, obtained byelectrolysis.● All of the metals from iron and belowin the reactivity series are relativelyeasy to obtain from their ores byheating.● Iron is obtained by reduction withcarbon monoxide● Tin is obtained by reduction withcarbon● Lead is obtained by heating leadsulfide in air to produce an oxide,which is then reduced with carbon.● Copper is obtained by controlledheating with the correct amount of air● Mercury is obtained by heating in air.© Diagram Visual Information Ltd.● Zinc114PATTERNS—METALSKey wordsoxidereactivityreactivity seriesReactivity summaryReactivity summary:metalsK NaCaMgAlZnPtAu1272PbPbO436AgAg2O61120 4CuCuO311Pt——AlAl 2O31114HgHgO182AuAu2O354ZnZnO697FeFe2O3548form oxides(e.g.,Na2O) inlimited suppliesof O2, butperoxides(e.g., Na2O2)with excess O2burn withdecreasingvigor toform oxidesReaction with oxygenHeat evolved whenmetal reacts with 1mole of O2 to formoxide shown / kJKK2 O723CaCaONaNa2O832MgMgOat the top of thereactivity series readily burn inoxygen.
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