University:
York University
Course:
CHEM 1001 | Chemical Dynamics
Academic year:

2022
Views:

148

Pages:

3
Author:

Niklas

Chapter 11 04/32/2022 04/25/2022 Electrolysis drive non-spontaneous reactions by applying electrical energy electrolysis cell contains two electrodes in a liquid solution or in a molten salt anode is where oxidation occurs anions migrate towards anode cathode is where reduction occurs cations migrate towards cathode Commercial applications of electrolysis Electrolysis of water H₂ and O₂ produced in a 2:1 stoichiometry Corrosion current (corrosion rate) depends on pH, presence of O₂, and H₂O oxidation: Fe → Fe²⁺ + 2e⁻; Fe²⁺ → Fe³⁺ + e⁻ reduction: O₂ + 4H⁺ + 4e⁻ → 2H₂O; 2H⁺ + 2e⁻ → H₂ (pH dependent) precipitation: Fe³⁺ + 3OH⁻ → Fe(OH)₃ → Fe₂O₃·xH₂O (rust) pH dependence: E = E₀ - (0.0592/n)log(1/[H⁺]³)^m difference in E values is constant (1.231 V) pH dependence of electrochemical reactions Corrosion horizontal line: reduction reaction vertical line: acid-base reaction Differential aeration corrosion mechanism rust in contact with air iron corrodes in the anaerobic region (not protected by surface oxide) Fe(s) → Fe²⁺ + 2e⁻ oxygen is reduced in the aerated region O₂ + 4H⁺ + 4e⁻ → 2H₂O [Diagram of a corrosion cell] rust precipitates at the water-metal interface (drying pattern on frying pan) Corrosion protection by passivation passivation by rust (hydrated Fe₂O₃) slows down Fe corrosion but doesn't stop it pitting corrosion occurs by differential aeration alloying Fe with Cr (stainless steel) passivates iron by forming a surface Cr₂O₃ layer Cathodic protection of iron Fe can be protected against corrosion by using a sacrificial anode anode is a metal more easily oxidized than Fe, more negative in series, and doesn't explode in H₂O O₂ reduction still happens on the Fe surface, but Zn is corroded instead of Fe