18'9 Batteries are Galvanic Cells Car Batteries

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18.9Batteries are Galvanic CellsCar Batteries
Slide 1

• Car batteries are lead storage batteries.
• Pb PbO2 H2SO4 PbSO4(s) H2O
• The typical 12V battery consists
• as 6 cells connected in series,
• each providing 2 V each.

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Dry Cell- common household batteries Patented in
1866 by a Frenchman George LaClanche

• It has a Zinc metal can , which serves as the
  anode and an inert graphite rod, surrounded by a
  paste of solid magnesium dioxide and carbon
  black, which functions as the cathode. (the dry
  cell is not completely dry but gets its name
  because the electrolyte is an aqueous paste
  rather than a liquid solution.
• The simplified equation is
• 2MnO2(s) H2O (l) 2e- ? Mn2O3(s)
  2NH3(aq) 2e-
• Zn (s) ? Zn2 (aq) 2e-

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BatteriesAlkaline

• Alkaline- a modified version of Leclanche cells,
  but the ammonium chloride electrolyte is replaced
  with either NaOH or KOH
• Less corrosion here because of the reaction
  taking place in a basic environment
• The simplified equation is
• Zn(s) 2OH-(aq) ZnO(s) H2O(l)
  2e-
• MnO2 H2O(l) 2e- M2O3(s)
  2OH-(aq)

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BatteriesNi-Cad
Slide 2

• NiCad unlike most dry cell batteries they are
  rechargeable
• They can be recharged many times because the
  solid products of the electrode reactions adhere
  to the surface of the electrode.
• Popular uses portable tools, calculators
• The simplified equation is
• Cd(s) 2OH-(aq) Cd(OH)2(s) 2e-
• NiO2(s) H2O e- Ni(OH)2

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18.10Corrosion
Slide 3

• Rusting - spontaneous oxidation.
• Most structural metals have reduction potentials
  that are less positive than O2 .
• Fe Fe2 2e- Eº 0.44 V
• O2 2H2O 4e- 4OH- Eº 0.40 V
• Fe2 O2 H2O Fe2 O3 H
• Reaction happens in two places.

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Slide 4
Salt speeds up process by increasing conductivity
Water
Rust
e-
Iron Dissolves- Fe Fe2
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Preventing Corrosion
Slide 5

• Coating to keep out air and water.
• Galvanizing - Putting on a zinc coat
• Has a lower reduction potential, so it is more.
  easily oxidized.
• Alloying with metals that form oxide coats.
• Cathodic Protection - Attaching large pieces of
  an active metal like magnesium that get oxidized
  instead.

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18.11Electrolysis
Slide 6

• Running a galvanic cell backwards.
• Put a voltage bigger than the potential and
  reverse the direction of the redox reaction.
• Used for electroplating.

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18.13Calculating plating
Slide 9

• Have to count charge.
• Measure current (in amperes)
• 1 amp 1 coulomb of charge per second
• Charge(C) Current(A) x t (s)
• Mole e- charge(C) x 1/96,500
• Current ? charge ? mol e- ? mole product
• and time
• 
  grams of product

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Slide 10
Other uses

• Electrolysis of water.
• Separating mixtures of ions.
• More positive reduction potential means the
  reaction proceeds forward.
• We want the reverse.
• Most negative reduction potential is easiest to
  plate out of solution.

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Homework

• 18.20
• 18.21
• 18.94