Eput,Faraday Law & Electrolysis 5(a)Rollno(57,58,59)
Transcript of Eput,Faraday Law & Electrolysis 5(a)Rollno(57,58,59)
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Parul Institute of Eng &Tech.
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Subject Code :150906
Name Of Subject : Electrical Power Utilization &
Traction.
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Houghton Mifflin Company and G. Hall.All rights reserved. 2
Name of Unit : Electrolytic process
Topic :Principle and Faraday law of Electrolysis
Name of Faculty : Pratik patel
Name of Studnets:
Dhameliya Chirag.(en.no-100370119019/rol no- 58)
Patel Brijesh.(en.no-100370119018/ rol no-57)
Gandhi Nirav.(en.no-100370119020/ rol no-59)
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Topic..
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Principle of faraday law.
Define electrolysis.
Values of DG and Ecell.
Electrolysis of water.
Some industrial application.
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Faraday's law
Faraday's 1st Law of
Electrolysis- The mass of a substance altered at
an electrodeduring electrolysisis directlyproportional to the quantity of
electricitytransferred at that electrode.
Quantity of electricity refers to the quantity
of electrical charge, typically measured
in coulomb
http://en.wikipedia.org/wiki/Electrodehttp://en.wikipedia.org/wiki/Electrolysishttp://en.wikipedia.org/wiki/Quantity_of_electricityhttp://en.wikipedia.org/wiki/Quantity_of_electricityhttp://en.wikipedia.org/wiki/Electrical_chargehttp://en.wikipedia.org/wiki/Coulombhttp://en.wikipedia.org/wiki/Coulombhttp://en.wikipedia.org/wiki/Electrical_chargehttp://en.wikipedia.org/wiki/Quantity_of_electricityhttp://en.wikipedia.org/wiki/Quantity_of_electricityhttp://en.wikipedia.org/wiki/Electrolysishttp://en.wikipedia.org/wiki/Electrode -
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Faraday's 2nd Law of
Electrolysis For a given quantity of D.C electricity
(electric charge), the mass of
an elementalmaterial altered at an
electrode is directly proportional to theelement'sequivalent weight. The
equivalent weight of a substance is
its molar massdivided by an integer thatdepends on the reaction undergone by
the material.
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http://en.wikipedia.org/wiki/Chemical_elementhttp://en.wikipedia.org/wiki/Equivalent_weighthttp://en.wikipedia.org/wiki/Molar_masshttp://en.wikipedia.org/wiki/Molar_masshttp://en.wikipedia.org/wiki/Equivalent_weighthttp://en.wikipedia.org/wiki/Chemical_element -
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Electrolysis
The splitting (lysing) of a substance ordecomposing byforcinga current
through a cell to produce a chemicalchange for which the cell potential isnegative.
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Electrolysis
electrolysisis a method of usinga directelectric current(DC) to drive
an otherwise non-spontaneous
chemical reaction. Electrolysis iscommercially highly important as a
stage in
the separationof elementsfromnaturally occurring sources such
as oresusing anelectrolytic cell.
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http://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Electrolysishttp://en.wikipedia.org/wiki/Chemical_elementhttp://en.wikipedia.org/wiki/Oreshttp://en.wikipedia.org/wiki/Electrolytic_cellhttp://en.wikipedia.org/wiki/Electrolytic_cellhttp://en.wikipedia.org/wiki/Electrolytic_cellhttp://en.wikipedia.org/wiki/Electrolytic_cellhttp://en.wikipedia.org/wiki/Oreshttp://en.wikipedia.org/wiki/Chemical_elementhttp://en.wikipedia.org/wiki/Electrolysishttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Direct_current -
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VoltaicElectrolytic
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Houghton Mifflin Company and G. Hall.All rights reserved. 9
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Fig. 21.17
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Increase
oxidizing
power
Increasereducing
power
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A standard electrolytic cell. A power source forces
the opposite reaction
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Electrolysis
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( ) A il l t d t t (b)
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(a) A silver-plated teapot. (b)
Schematic of the electroplating
of a spoon.
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Schematic of the
electroplating of a spoon.
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AgNO3(aq)
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Electrolysis of water
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Electrolysis of water
At the anode (oxidation):
2H2O(l) + 2e-= H2(g) + 2OH
-(aq) E=-0.42V
At the cathode (reduction): 2H2O(l) = O2(g) + 4H
+(aq) + 4e- E= 0.82V
Overall reaction after multiplying anodereaction by 2,
2H2O(l) = 2H2(g) + O2(g)
Eocell= -0.42 -0.82 = -1.24 V
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Electrolysis: Consider the electrolysis of a solution
that is 1.00 M in each of CuSO4(aq) and NaCl(aq)
Oxidation possibilities follow. 2Cl(aq) = Cl2(g) + 2e
E =1.358 V
2SO42(aq) = S2O8
2(aq) + 2eE =2.01 V
2H2O = 4H+(aq) + O2(g) + 4e
E =1.229 V
Reduction possibilities follow:
Na+(aq) + e= Na(s) E =2.713V
Cu2+(aq) + 2e= Cu(s) E = +0.337V
2H2O + 2e= H2(g) + 2OH
(aq) E = +0.828V
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Electrolysis
We would choose the production of O2(g) and Cu(s). But the voltage for producing O2(g) from solution is
considerably higher than the standard potential, because ofthe high activation energy needed to form O2(g).
The voltage for this half cell seems to be closer to1.5 V inreality.
The result then is the production of Cl2(g) and Cu(s).anode, oxidation: 2Cl(aq) = Cl2(g) + 2e
E =1.358 V
cathode, reduction: Cu2+(aq) + 2e: Cu(s) E = +0.337 V
overall: CuCl2(aq) : Cu(s) + Cl2(g) E =1.021 V
We must apply a voltage of more than +1.021 V to cause thisreaction to occur.
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Stoichiometr of electrol sis
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Stoichiometry of electrolysis:
Relation between amounts of
charge and product Faradays law of electrolysis relates to
the amount of substance produced ateach electrode is directly proportionalto the quantity of charge flowingthrough the cell (half reaction).
Each balanced half-cell shows the
relationship between moles ofelectrons and the product.
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Application of Faradays law
1. First balance the half-reactions to findnumber of moles of electrons needed permole of product.
2. Use Faraday constant (F = 9.65E4 C/mol
e-) to find corresponding charge. 3. Use the molar mass of substance to find
the charge needed for a given mass ofproduct. 1 ampere = 1 coulomb/second or 1 A = 1 C/s
A x s = C
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Stoichiometry of Electrolysis
How much chemical change occurs with theflow of a given current for a specified time?
current and time quantity of charge
moles of electrons moles of analyte
grams of analyte
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Fig. 21.20
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Doing work with electricity.
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Industrial Applications of Electrolysis
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What chemical species would be present in a
vessel of molten sodium chloride, NaCl (l)?
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Na+ Cl-
Lets examine the electrolytic cell for molten NaCl.
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+- battery
Na (l)
electrodehalf-cell
electrodehalf-cell
Molten NaCl
Na+
Cl-
Cl- Na+
Na+
Na+
+ e-
Na 2Cl-
Cl2 + 2e-
Cl2(g) escapes
Observe the reactions at the electrodes
NaCl (l)
(-)
Cl-
(+)
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+- batterye-
e-
NaCl (l)
(-) (+)
cathode anode
Molten NaCl
Na+
Cl-
Cl-
Cl-
Na+
Na+
Na+
+ e-
Na 2Cl-
Cl2 + 2e-
cationsmigratetoward
(-)electrode
anionsmigratetoward
(+)electrode
At the microscopic level
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Molten NaCl Electrolytic Cell
cathode half-cell (-)REDUCTION Na+ + e-Na
anode half-cell (+)OXIDATION 2Cl-Cl2 + 2e
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overall cell reaction2Na+ + 2Cl- 2Na + Cl2
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X 2
Non-spontaneous reaction!
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The Downs Cell for the Electrolysis of Molten Sodium Chloride
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If the products are mixed, the result is household bleach.
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e p oduc s a e ed, e esu s ouse o d b eac
2 NaOH(aq) + Cl2(g) = NaCl(aq) + NaOCl(aq) + H2O
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The Mercury Cell for Production of Chlorine and Sodium
Hydroxide
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A schematic diagram of an
electrolytic cell for producing
aluminum by the Hall-Heroultprocess.
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Fig. 22.19 A
schematic diagram
of an electrolytic
cell for producingaluminum by the
Hall-Heroult
process.
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The Hall Process for
Aluminum Electrolysis of molten Al2O3 mixed with
cryolitelowers melting point
Cell operates at high temperature1000oC
Aluminum was a precious metal in 1886.
A block of aluminum is at the tip of theWashington Monument!
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graphite anodes e-
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carbon-lined steel vesselacts as cathode
CO2bubbles
Al (l)Al2O3(l)
DrawoffAl (l)
-
+
Cathode: Al+3 + 3e- Al (l)
Anode: 2 O-2 + C (s) CO2(g) + 4e-
from
powersourceAl+3
O-2
O-2Al+3
O-2
graphite anodes
e-
e
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The Hall Process
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Cathode: Al+3 + 3e- Al (l)
Anode: 2 O-2 + C (s) CO2 (g) + 4e-
4 Al+3+ 6 O-2 + 3 C (s) 4 Al (l) + 3 CO2(g)
x 4
x 3
The graphite anode is consumed in the process.
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: Production of solid Mg
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Thankyou.............