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IMG_0001_NEW_0037 - Iflayer get scratched Zn oxidised...

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TODAY'S LECTURE: "Electrochemistry" . Corrosion prevention . Electrolysis . Commercialelectrolytic processes Eledtrolysis Electrolysis : force current through a cell to produce a chemical change for which the cell potential is negative Use electrical energy to make a non- spontaneous process occur Example: for the redox reaction Cu -+ Crf* + 2e Zn2* + 2{ -+ Zn _E: _(+0.34 E" : -0.76Y Cu * Zrf* -+ Cu2' Not spontaneous + potential > 1.10 V + Zn Enr: -1.10 V need to apply a electrical for redox reaction to occur CNN Electrolvtic cell Steel Gorrosion Prevention Steel: alloy: Fe + C (0.02 - 1.7%) + Mg, S, P, Si ... Rusting of steel = rusting of iron Fe _+ Fd* + 2e- _8": _(_0.44 V) Methods for preventing steel corrosion: . Coatings: paint, metal plating . Sacrificial coating - Zncoating: galvanizing -+ Zinc oxide layer
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Unformatted text preview: - Iflayer get scratched: Zn oxidised rather than Fe Zn _+ Zrf+ + 2e_ _6" : _(_0.76 V) . Stainless steel > 10.5 Yo Cr thin layer impewious to HrO and O, (air) CrrOr: passivation layer -+ much higher E" . Cathodic protection Connect more active metal to protect steel- Example: Mg or tudk\.r ;:':Hr,":fllhm agent than .i,* i***r, Cr + Or(air) -+ CrrO, Quantitative Electrolysis How much product it produced if the current is passed for a certain time? 4 Step calculation: Step 1: Current measured in Amperes (Amps) I Amo: I Coulomb of charee oer second . Coulombs of charge : amps x seconds = 9 r. " Step 2: Moles of electrons : Coulombs of charge Charge on I mole of e-s Charge on I mole of e-s : I Faraday Quantity ofcharge (Coulombs) Grams of product...
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