Slide 1

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


Slide 2


Slide 3

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


Slide 4

Electrolysis
Preparation of Aluminum (Hall process)


Slide 5

Electrolytic Refining of Copper
Cu(s) + Cu+2(aq) --> Cu+2(aq) + Cu(s)
impure
pure
anode
cathode
impurities: anode mud; Ag, Au, Pb


Slide 6


Slide 7

Quantitative Aspects of Electrolysis
• 1 coulomb = 1 amp sec
• 1 mole e- = 96,500 coulombs


Slide 8

Electroplating
EXAMPLE: How many grams of chromium
can be plated from a Cr+6 solution in 45
minutes at a 25 amp current?


Slide 9

Electroplating
EXAMPLE: How many grams of chromium
can be plated from a Cr+6 solution in 45
minutes at a 25 amp current?
(45 min)
#g Cr = ------------


Slide 10

Electroplating
EXAMPLE: How many grams of chromium
can be plated from a Cr+6 solution in 45
minutes at a 25 amp current?
definition of minute
(45 min)(60 sec)
#g Cr = --------------------(1 min)


Slide 11

Electroplating
EXAMPLE: How many grams of chromium
can be plated from a Cr+6 solution in 45
minutes at a 25 amp current?
(45) (60 sec) (25 amp)
#g Cr = --------------------------(1)


Slide 12

Electroplating
EXAMPLE: How many grams of chromium
can be plated from a Cr+6 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)


Slide 13

Electroplating
EXAMPLE: How many grams of chromium
can be plated from a Cr+6 solution in 45
minutes at a 25 amp current?
Faraday’s constant
(45)(25)(60)(1 C)(1 mol e-)
#g Cr = ---------------------------------(1)(1)(96,500 C)


Slide 14

Electroplating
EXAMPLE: How many grams of chromium
can be plated from a Cr+6 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-)


Slide 15

Electroplating
EXAMPLE: How many grams of chromium
can be plated from a Cr+6 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


Slide 16


Slide 17

Corrosion
O2(g) + 4 H+(aq) + 4 e- -----> 2 H2O(l)
Eo = 1.23 V

Rusting
Fe(s) -----> Fe+2(aq) + 2 e-

Eo = 0.44 V

O2(g) + 4 H+(aq) + 4 e- -----> 2 H2O(l)

Eo = 1.23 V

-------------------------------------------

--------------

2 Fe(s) + O2(g) + 4 H+(aq) ----->
2 H2O(l) + Fe+2(aq)

Eo = 1.67 V


Slide 18

Preventing Corrosion
painting
galvanizing
sacrificial anode