Eput,Faraday Law & Electrolysis 5(a)Rollno(57,58,59)

8/11/2019 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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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

-

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.............

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Eput,Faraday Law & Electrolysis 5(a)Rollno(57,58,59)