Oxidation-Reduction ReactionsOxidation-Reduction ReactionsOXIDATION = loss of electrons

Examples:

Na Na+ + e-

Al Al3+ + 3e-

S2- S + 2e-

OXIDATION = increasing the oxidation number (more positive)

Example:

NO NO2 -2+2 -2+4

change = +2

+2 to +4 : N is oxidized

LEO the lion goes GER

Oxid. Nos:

Oxidation-Reduction ReactionsOxidation-Reduction Reactions

REDUCTION = gain of electrons

Examples: N + 3e- N3-

Fe3+ +e- Fe2+

REDUCTION = decreasing the oxidation number (more negative)

Example:

MnO4- Mn2+

Oxid. Nos: +7 +2

change = -5

+7 to +2 : Mn is reduced

LEO the lion goes GER

Voltaic CellsVoltaic Cells(a porous barrier can be used instead of salt bridge)

Choose any two entries; the top one will act as the

cathode and will be reduced; the bottom one will act as the anode and

will be oxidized.

This electromotive series presents data showing thetendency of substances to

gain or lose electrons.

The standard voltage will be the algebraic difference between the two respective

potentials.

0.46 V

BatteriesBatteriesBatteries are the most practical applications of voltaic cell.All batteries have self contained anode/cathode compartments.All operate using the same principles already discussed.

The Classic “dry” (LeClanché) cell.

carboncathode

zincanode

Mushy pasteOf MnO2 andNH4Cl

Overall reaction:

Zn + 2 MnO2 + 2NH4+→

Zn2++2MnO(OH)+ 2NH3

E~1.5 v.

BatteriesBatteries

Alkaline Battery (similar to dry cell but more efficient)Alkaline Battery (similar to dry cell but more efficient)Anode: (Zn cap) Zn(s) Zn2+ (aq) + 2e-

Cathode: MnO2, NH4Cl and C paste:

2NH4+(aq) + 2MnO2(s) + 2e- Mn2O3(s) + 2NH3(aq) + 2H2O(l)

BatteriesBatteriesLead-Acid BatteryLead-Acid Battery

Six cells in seriesgive a total voltageof ~12 volts in anautomobile battery.

BatteriesBatteriesFuel CellsFuel Cells

CorrosionCorrosion is the entropy monster’s greatest weapon.It is the evil side of REDOX.It costs 100s of billions of dollars yearly to prevent and correct.Basically, it is the spontaneous process (oxidation) of iron:

Fe → Fe2+ + 2e-

nice shiny metal (steel) ugly brownish-red

powder ……….RUST!

Rusting cannot occur by itself.

Can’t have only the OX in REDOX; So, what gets reduced?

Usually H2O or O2

CorrosionCommon type of “rusting” redox: (Eo ~ 0.8 V)

O2(g) + 4H+(aq) + 2Fe(s) → 2Fe2+(aq) + 2H2O(l)Easy, but even more favorable in acid conditions. There are similar equations also involving water.

Stopping Corrosion1. Galvanize it (coat with Zn). Fe has higher SRP than

Zn. Coupled with Zn, Fe is the cathode (cathodic protection) (look for a “matte” appearance of Zn).

2. Use “sacrificial metal” such as Mg – (this is also cathodic protection).

3. Cover it (paint).4. Create rust-resistant alloys, e.g., stainless steel

(Fe/Ni/Cr), or nickel steels (Fe/Ni).

CorrosionCorrosionPreventing the Corrosion of IronPreventing the Corrosion of Iron

Also used onships to prevent

corrosion

Electrolysis Electrolysis – Electrolysis of Molten Salts– Electrolysis of Molten Salts

Cathode: 2Na+(l) + 2e- 2Na(l)

Anode: 2Cl-(l) Cl2(g) + 2e-

Industrially, electrolysis is used to produce metals like aluminum (Hall-Héroult process, where Al2O3 is electrolyzed in molten cryolite, Na3AlF6, with a carbon electrode to give an overall reaction of 2Al2O3 + 3C 4Al + 3CO2)

Decomposition of molten NaCl

cathode:Au+(aq) +e-→Au

anode:Au→Au+(aq) +e-

external power source

Au

Au+(aq) Au+(aq)

Au

external power source

Electrolysis with Active Electrodes –Electrolysis with Active Electrodes –

Gold plating – protects against corrosionGold plating – protects against corrosion

Major kinds of organic compounds in living systems:Hydrocarbons – contain only C and HCarbohydrates (saccharides; sugars) – CH2O general formulaFats and fatty acids – C-C-C-C-C-C-C-C-C-C-C-C-CO2HProteins – contain C, H, O, and N (sometimes S)

Hydrocarbons – CHMethane – CH4 (simplest hydrocarbon)Propane C3H8

Butane C4H10

Octane – C8H10 (gasoline)Kerosene – C12H26 (diesel and jet fuel)Oils - C20H42

Asphalt C100-H202

Carbohydrates – (CH2O)x

Monosaccharides – C6H12O6 – fructose – corn sugar, fruit sugar (sweetist) - glucose – blood sugar, wine sugar (least sweet)

Organic compounds come from organisms (original definition), but arerecognized as always containing carbon atoms, generally in chains

Amylose

Cellulose

Disaccharides – C12H22O12 – sucrose – table sugar, cane sugar, beet sugar (intermediate sweetness)Lactose – milk sugarMaltose – malt sugar

Polysaccharides - (C6H12O6)x where x is very largestarch – digestiblecellulose – digestible only by microorganisms

Proteins – made up of amino acidsThere are 20 different amino acids -NH2-R-CO2HGlobular proteins – enzymes (example, hemoglobin)Fibrous proteins – structural (muscle, hair, skin, animal tissue)

Fats – made up of fatty acids and glycerolFatty acids – CH3CH2CH2CH2CH2CO2H, or some other even number ofcarbon atoms. Examples: C-CO2H acetic acid (vinegar)C-C-C-CO2H butyric acid (rancid butter)C-C-C-C-C-CO2 caproic acid (goat and other barnyard animalsC-C-C-C-C-C-C-C-C-C-C-C-C-C-C-CO2 palmitic acid (palm oil)C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-CO2H stearic acid (animal fats)

Sulfur organic compounds:skunk smell, cabbage, onions, garlic, rotten eggs, oil refinery areas

Nitrogen organic compounds:amines (fishy odors)decaying flesh (cadaverine)

Fatty acids: animal smells, spoiled beer

ethylene is the simplest hormone – CH2=CH2 – ripens fruits

oleic acid C-C-C-C-C-C-C-C-C=C-C-C-C-C-C-C-C-CO2H in olive oilthe C=C is “unsaturation”