Oxidation/Reduction& Batteries

Oxidation

• Combining with Oxygen – combustion

• Gives off energy

• Oxidation in the body – H2O and CO2

• Oxidation in an engine – above plus CO and NOx’s– Degree of oxidation – CO not totally oxidized

• Rusting of Iron

Oxidation

• Gaining oxygen or loosing electrons

2Na + Br2 → 2Na+ + 2Br- → 2NaBr

• Which looses electrons?

• F, Cl, Br, I are common oxidizing agents

• Oxidizing agents cause other substances to be oxidized

Reduction

• Oxidation/Reduction like Acid/Base– Always in pairs– Instead of exchanging protons, exchanging:

• Electrons• Oxygen

• Losing oxygen or gaining electrons– Memory table

• Metal ores are oxidized metals, must be reduced

Reduction

• Reducing agents cause other substances to be reduced.

• What are anti-oxidants?

Reduction

• Anti-oxidants are electron donors– Reduce potential oxidizing agents

• Free radicals – unpaired electron wants another• Takes electrons – oxidizes

• Vitamins A, C, and E

Strengths of Redox Agents

• So zinc is more active than copper

• So iron is more active than copper

• Is iron or zinc more active? – How do you tell?

• The more active a metal is, the more it wants to be oxidized or ionized.

Zn + Cu Zn + Cu(s)2+(aq)

2+(aq) (s)

Fe + Cu Fe + Cu(s) (s)2+(aq)

2+(aq)

Zn + Fe Zn + Fe(s) (s)2+(aq)

2+(aq)

Batteries

• Based on activity of metals, etc.– Something oxidized that wants to be reduced– Something reduced that wants to be oxidized

Batteries

• Based on activity of metals, etc.– Something oxidized that wants to be reduced– Something reduced that wants to be oxidized

• Store electricity as chemical energy• Primary batteries – cannot be recharged

– Dry cells, alkaline, lithium

• Secondary batteries – rechargeable– NiCad, NiMH, Lead acid, rechargeable

alkaline, Lithium ion

• Which is better for the environment?

Lead Acid Batteries(car batteries)

Pb +PbO +2H SO 2PbSO + 2H O + e ( s) 2( s) 2 24( aq) 4( s)-

•During recharging the following also occurs:

2H O 2H + O2 2 2

•Is there a danger here?

H28 – C12

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