chapter 8 - oxidation and reduction

mnemonics for oxidation and reduction

LEO: loss of electrons is oxidation
GER: gain of electrons is reduction

oxidizing agents

cause oxidation

reducing agents

cause reduction

oxidation and reduction reactions

can be used to produce electricity

electrodes

pieces of metal where electrons are transferred

anodes

electrodes where oxidation occurs

cathodes

electrodes where reduction occurs

half-reactions

oxidation: Cu(s) → Cu²⁺(aq) + 2e^-
reduction: 2Ag⁺(aq) + 2e^- → 2Ag(s)

dry cell

Zn + 2MnO₂ + H₂O → Zn²⁺ + Zn²⁺ + Mn₂O₃ + 2OH^-

lead storage batteries

discharge: Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O
recharge: 2PbSO₄ + 2H₂O → Pb + PbO₂ + 2H₂SO₄

nickel-cadium batteries

used in portable radios and cordless appliances. use candium anodes and nickel-oxide cathodes

fuel cells

fuel is oxidized at the cathode and O₂ is reduced at the cathode. the electrons are allowed to flow through a wire and do work

rusting of iron

2Fe + O₂ + 2H₂O → Fe(OH)₂
4Fe(OH)₂ + O₂ + 2H₂O → 4Fe(OH)₃

protection of aluminum

aluminum is more reactive than iron. however, corrosion of aluminum is not a serious problem, aluminum oxide is very tough and prevents further corrosion

silver tarnish

the result of the oxide on the silver surface reacting with hydrogen sulfide. (H₂S) in air. leaves a black film of silver sulfide (Ag₂S)
polishing the tarnished silver will restore the shine but at the expense of some of the silver metal

chemical explosions

can be the result of redox reactions. redox reactions that occur rapidly with the production of gases (such as nitrogen) are often explosive
ANFO: ammonium nitrate/fuel oil

oxygen

most common oxidizing agent

ozone (O₃)

a powerful oxidizing agent. in the lower atmosphere it is harmful to both plants and animals, however in the stratosphere it serves to protect life on earth from harmful ultraviolet radiation

hydrogen peroxide (H₂O₂)

a common oxidizing agent used as a disinfectant or to bleach hair

potassium dichromate (K₂Cr₂O₇)

oxidize alcohols and turns green when reduced to chromium (III)

benzyl peroxide

an antiseptic and used to treat acne

chlorine

used as a disinfectant in treatment of drinking and wastewater

bleaches [NaOCl, Ca(OCl)₂]

oxidizing agents used on fabrics

metallurgy reducing agents

coke (c) is produced by heating coal to drive off volatile compounds

antioxidants

reducing agents in foods

hydrogen gas

prepared by reacting zinc with hydrochloric acid

photosynthesis

the only process that produces the elemental oxygen that is essential for animals on earth