Electrolysis

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Electrolysis

• non-spontaneous reaction is caused by the passage
  of an electric current through a solution

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Electrolysis

• Electrolysis of Sodium chloride
• (chlor-alkali process)
• molten reactants gt liquid sodium and chlorine
  gas
• aqueous reactants gt caustic soda (sodium
  hydroxide) and chlorine gas

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Electrolysis

• Preparation of Aluminum (Hall process)

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Electrolytic Refining of Copper

• Cu(s) Cu2(aq) --gt Cu2(aq) Cu(s)
• impure
  pure
• anode
  cathode
• impurities anode mud Ag, Au, Pb

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Quantitative Aspects of Electrolysis

• 1 coulomb 1 amp sec
• 1 mole e- 96,500 coulombs

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Electroplating

• EXAMPLE How many grams of chromium can be plated
  from a Cr6 solution in 45 minutes at a 25 amp
  current?

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Electroplating

• EXAMPLE How many grams of chromium can be plated
  from a Cr6 solution in 45 minutes at a 25 amp
  current?
• (45 min)
• g Cr ------------

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Electroplating

• EXAMPLE How many grams of chromium can be plated
  from a Cr6 solution in 45 minutes at a 25 amp
  current?
• definition of minute
• (45 min)(60 sec)
• g Cr ---------------------
• (1 min)

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Electroplating

• EXAMPLE How many grams of chromium can be plated
  from a Cr6 solution in 45 minutes at a 25 amp
  current?
• (45) (60 sec) (25 amp)
• g Cr ---------------------------
• (1)

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Electroplating

• EXAMPLE How many grams of chromium can be plated
  from a Cr6 solution in 45 minutes at a 25 amp
  current?
• definition of a coulomb
• (45)(60 sec)(25 amp)(1 C)
• g Cr -----------------------------
• (1) (1 amp sec)

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Electroplating

• EXAMPLE How many grams of chromium can be plated
  from a Cr6 solution in 45 minutes at a 25 amp
  current?
• Faradays constant
• (45)(25)(60)(1 C)(1 mol e-)
• g Cr ----------------------------------
• (1)(1)(96,500 C)

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Electroplating

• EXAMPLE How many grams of chromium can be plated
  from a Cr6 solution in 45 minutes at a 25 amp
  current?
• atomic weight
• (45)(60)(25)(1)(1 mol e-)(52 g Cr)
• g Cr ------------------------------------------
  -
• (1)(1)(96,500) (6 mol e-)

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Electroplating

• EXAMPLE How many grams of chromium can be plated
  from a Cr6 solution in 45 minutes at a 25 amp
  current?
• (45)(60)(25)(1)(1 mol e-)(52 g Cr)
• g Cr ------------------------------------------
  -
• (1)(1)(96,500)(6 mol e-)
• 58 g Cr

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Corrosion

• O2(g) 4 H(aq) 4 e- -----gt 2 H2O(l)
• Eo 1.23 V
• Rusting
• Fe(s) -----gt Fe2(aq) 2 e- Eo 0.44 V
• O2(g) 4 H(aq) 4 e- -----gt 2 H2O(l) Eo
  1.23 V
• -------------------------------------------
  --------------
• 2 Fe(s) O2(g) 4 H(aq) -----gt
• 2 H2O(l) Fe2(aq) Eo 1.67 V

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Preventing Corrosion

• painting
• galvanizing
• sacrificial anode