HSC CHEMISTRY OPTION: SHIPWRECKS, CORROSION & CONSERVATION

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1 HSC Chemistry Year 2014 Mark Pages 6 Published Feb 9, 2017 HSC CHEMISTRY OPTION: SHIPWRECKS, CORROSION & CONSERVATION By Sahar (99.1 ATAR)

2 Pwered by TCPDF ( Yur ntes authr, Sahar. Sahar achieved an ATAR f 99.1 in 2014 while attending Carlingfrd High Schl Currently studying Bachelr f Science/ Master f Optmetry at The University f New Suth Wales Achievements: Premier's Award fr All-rund Excellence in the NSW HSC (2014) First Place in Mathematics (at attended schl) Hrnsby Shire Cuncil Award fr Academic Achievement (2014) Distinguished Achievement Award in 2014 HSC Sahar says: I achieved a Band 6 in all these subjects: English Advanced (93), Mathematics (97), Mathematics Extensin 1 (92), Ecnmics (95), Bilgy (92) and Chemistry (90). Withut my ntes, I wuldn't have been able t achieve an ATAR f They are very rganised and include diagrams, graphs and tables in relevant sectins t assist learning. These ntes will help yu succeed and reach yur HSC gals!

3 Mdule 5 Shipwrecks, crrsin and cnservatin Chapter 20 The Ocean Envirnment Main ins in ceans chlride and sdium with smaller amunts f sulfate, magnesium and calcium Leaching by rainwater frm terrestrial envirnments physical and chemical weathering f rcks and sils by rainwater, rivers and undergrund water disslved minerals transprted t seas and ceans Hydrthermal vents in mid-cean ridges (magma released as tectnic plate diverge) water in cntact with magma becmes superheated leaching f minerals in surrunding rcks (slubility f salts increase at high temps) disslved minerals gradually dispersed thrughut ceans Redx reactins invlve transfer f electins (prcess f xidatin and reductin) Occurs when reactants are in direct cntact, thrugh metal/graphite cnductr r by mvement f ins in electrlyte (slutin is necessary fr reactin as ins cannt mve ut f crystal lattice when slid) Galvani experimented with frg legs t shw that muscular cntractin ccurred using static electricity Twitching ccurred when spinal crds were cnnected by cpper hks t irn railing (n static charge) Discvered that muscles twitch when tw different metals frm circuit with muscle tissue Cncluded that tissue cntained animal electricity which activated nerves in prcess Vlta develped Vltaic Pile by alternating disks f zinc and silver with each pair separated by cardbard r clth saked in cncentrated salt slutin caused rejectin f animal electricity Incrrectly believed that cntact between tw metals generated electric current Davy passed electric currents thrugh mlten salts f cmpunds allwing islatin f alkali elements (K, Na) and alkaline earth elements (Ba, Ca, Mg) decmpsitin f electrlytes Crrectly reasned that electric currents in Vltaic Pile were generated by chemical changes Faraday develped quantitative laws (laws f electrlysis) relating quantity f electric charge transferred and mass f prducts frmed during electrlytic decmpsitin reactins Used t calculate mass f materials prduced at electrdes when knwn amunt f charge is transferred Wrk emphasised imprtance f in mvement in electrlyte and chemical changes caused at electrdes Crrsin redx reactin in which a metal becmes wrn away e.g. rusting crrsin f irn Active metals crrde when expsed t xygen e.g. Mg, Ca frming metal xide (nt reactive - Ag, Pt) Water usually accelerates prcess surface xides disslve, diffuse away expsing new metal t crrde Passivating metals active metals that d nt crrde readily due t thin cating f metal xide which frms n metal s surface (prtective layer which prevents further reactin between metal and xidising agent) Strngly bnded, chemically unreactive cating refrms again if remved Aluminium resistance t crrsin negated by presence f salt (prus layer frmed) Cnditins under which rusting ccurs: - Surface which can act as ande (irn metal surface) - Surface that can act as cathde (impurity within irn) - Pathway fr flw f electrns - Pathway fr flw f ins (in case f rusting, is water) - Oxygen present (alng with water, reduced t frm hydrxide ins) Presence f salt, cntact with ther less active metals (act as cathde), acidic envirnment, impurities and stressing irn (atms less tightly bnded tgether break away mre easily) accelerate rate f rusting Main metals used t cnstruct ships since late 18 th century irn and irn allys (steel) cntains less than 2% carbn and varying amunts f ther metals Prperties: - Pure sheet irn: malleable and readily welded - Steel: harder, greater mechanical strength 1

4 Carbn steel varying amunts f carbn and small amunts f manganese, silicn, cpper (allys generally harder than pure metals different-sized atms f ther elements disrupt rderly arrangement f atms in metal lattice preventing them sliding ver each as easily ) Structural material in cean-ging ships (strength and ecnmical price) Different steels in ther parts e.g. stainless steel (resistant t rusting) fr fittings, tl steel (extra strength, hardness and resistance t wear) fr engines Steel: Cmpsitin: Prperties: Uses: Mild <0.2% C Sft and malleable. Crrdes fairly rapidly. Pipes. Nuts and blts. Rfing. Shipbuilding. Structural % C Hard and malleable. High tensile strength. Crrdes fairly rapidly. Beams and Girders. Railways. Reinfrcing fr buildings. Stainless 10-20% Cr 5-10% Ni Hard. Takes a high plish. Very resistant t crrsin. Fd prcessing machinery. Kitchen sinks and appliances. Cutlery. Surgical instruments. Razr blades. Electrlysis electrchemical prcess in which nn-spntaneus redx prcess is frced t ccur by applicatin f external current Mlten salts catin is reduced at cathde, anin frm salt xidised at ande Aqueus slutins at ande nitrate and sulfate never xidised, chlride xidised nly is relatively cncentrated, water ften xidised prducing xygen, nn-inert electrde may xidise Aqueus slutins at cathde metal ins f less reactive metals (Cu, Ag) reduced in preference t H 2 O but H 2 O reduced in preference t metal ins f reactive metals (Na, Mg, Al) Effect f cncentratin increasing cncentratin f catins r anins can alter prducts f electrlysis E.g. Electrlysing lw NaCl cncentratin causes water t be preferentially xidised ver chlride Electrlysing high NaCl cncentratin causes nly chlrine t be prduced at ande Nature f electrlyte (mlten r aqueus) mlten electrlytes with inert electrdes can yield nly ne prduct at each electrde while in aqueus slutin there is pssibility that H 2 O will be reactant at electrde Nature f electrdes (inert r active) carbn and platinum electrdes are inert as they are rarely invlved in electrlysis reactin (prvide surface fr electrn transfer) while nn-inert may partake in reactin 2

5 Pwered by TCPDF ( Histrical develpments in materials used in cnstructin f cean-ging vessels: - Earliest ships: made frm lcally available materials (e.g. animal skins, lgs) - Irn Age (750 BC): develpment f strnger tls ships made frm wden planks, cpper ally nails and fasteners replaced by irn (strnger) Wden hulls caulked (seems made watertight) but still prne t leaks and attack by marine wrms - Metals and allys first used as fittings fr wden bats (wrught irn and brnze used t make rudders, anchrs in Middle Ages) - 17 th century: lead sheeting cvered hulls t prevent marine wrms attacking wd (sft, malleable) later replaced by cpper sheeting (bicide discurages grwth f marine rganisms n hull) which was nailed with cpper nails Irn nails replaced cpper (1500 AD) caulked t prevent cntact with cpper which wuld cause galvanic crrsin f nails (cpper expensive nt used n all ships) - Brass sheeting replaced cpper (ht brass rlled t frm flexible plates, cheaper, crrded mre slwly) - Late 18 th century: sheet irn bats replaced cpper-ally bats (regular dry dcking and cleaning t remve rust and barnacles but advantageus ver wd ecnmical, nt set alight by cannns, faster) - Strng structural steel develped steel ships used (lighter, durable, versatile) Mdern methds f crrsin preventin in ships incrpratin f metals int steel t imprve prperties (e.g. Cr, Al, Ti added fr strength and t remain relatively free frm rust) Ways in which steel hulls may be prtected in marine envirnments: Crrsin resistant metals use f passivating metals (e.g. Cr which frms layer f Cr (III) xide) allyed t steel gives hull crrsin resistance (high chrmium-nickel stainless steels) Still subject t crevice crrsin in lwer O 2 envirnments (used in high O 2 envirnments abve water line since chlrides destry passivating layer) Cpper-nickel allys used fr sheathing (prtective cvering) in marine envirnments (crrsinresistant layer frms n surface) Develpment f surface allys can be prduced using laser techniques (Cr and Ni strngly bund t surface layers f steel by bmbarding surface with their ins at high temps) Steel surface frms passivating layer as Cr atms react with O 2 Al des nt frm strng passivating layer in presence f salt New paints plymer-based paints prevent steel surfaces cming int cntact with water and air Cnductive plymer paints (e.g. plyaniline) prmte frmatin f passivating layer between steel and paint Rustmaster reacts with surface f steel t frm mineral pyraurite (barrier against crrsin) Antifuling paints cntaining rganic plymers f zinc prtect ship hulls frm marine grwths that increase drag in water Sacrificial ande metal that xidises preferentially t prtect anther metal frm crrsin (need t be regularly replaced) Cathdic prtectin metal prtected frm crrsin by making it cathde in galvanic cell (electrns supplied t metal t suppress metal disslutin) Galvanising irn with layer f zinc prtects it frm rusting since zinc has mre psitive xidatin ptential allwing it t act as sacrificial ande zinc reacts with water and carbnate frming impervius layer f zinc carbnate ver irn restring prtectin Electrlyte cmpletes circuit and steel cathdically prtected Mg ande: Fe cathde: Marine envirnments lumps f zinc can be attached t hulls f ships, zinc cllars and plates used t prtect rudders and prpeller shafts Wet terrestrial envirnments magnesium andes attached t undergrund petrl strage tanks r zinc andes attached t pipelines carrying il r gas 3