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Lec . 2Lec . 2Faraday’s LawsFaraday’s Laws

Lec . 2Lec . 2Faraday’s LawsFaraday’s Laws

Industrial Electrolytic ProcessesIndustrial Electrolytic Processes““Electrolysis”Electrolysis”

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What you should learn

• What is electrolysis? • Faraday's laws of

electrolysis• Industrial Applications of

electrolytic process

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It is used industrially in a number of ways:1. Electroplatig.2. The preparation of gases, notably

chlorine.3. Water decomposition.4. The extraction of metals, notably

aluminum, magnesium, and sodium. 5. The refining of metals, such as copper

and zinc.

2. Electrolysis of Molten 2. Electrolysis of Molten Salts and Production of Salts and Production of

Cl2Cl2

2. Electrolysis of Molten 2. Electrolysis of Molten Salts and Production of Salts and Production of

Cl2Cl2

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+-battery

Na (l)

Cathode

Anode

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-

(+)

Molten NaCl Electrolytic Cell

cathode half-cell (-)REDUCTION Na+ + e- Na

anode half-cell (+)OXIDATION 2Cl- Cl2 + 2e-

overall cell reaction2Na+ + 2Cl- 2Na + Cl2

X 2

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Electrolysis of Diluted Electrolysis of Diluted NaClNaCl

battery+- power

source

e-

e-

NaCl (aq)

(-) (+)

cathodedifferent half-cell

Aqueous NaCl

Na+

Cl-

H2O

What could be reduced at the cathode?

Aqueous NaCl Electrolytic Cell

possible cathode half-cells (-)REDUCTION Na+ + e- Na

2H20 + 2e- H2 + 2OH-

possible anode half-cells (+)OXIDATION 2Cl- Cl2 + 2e-

2H2O O2 + 4H+ + 4e-

overall cell reaction2Cl- + 2H20 H2 + Cl2 + 2OH-

3. Water electrolysis3. Water electrolysis3. Water electrolysis3. Water electrolysis

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The Electrolysis of Watercontaining some sulfates

2 H2O + 2e- H2 (g) + 2 OH-

cathode reaction2H2O O2 (g) + 4H+ + 4e-

anode reaction

Cell diagram Battery, a source of direct currente- flow

Cathode Anode

e- flow

aqueous K2SO4

O2 gasH2 gas

+ pole of battery- pole of battery

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The Electrolysis ofwater

O 2H OH 2 isreaction overall The

OH 4 4H O H 2 OH 6reaction Cell

)2OH H2e- OH 2(2reaction Cathode

e 4 H 4 O OH 2 reaction Anode

2(g)2(g)2

OH 4

-2(g)2(g)2

-2(g)2

-2(g)2

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4. Extraction of 4. Extraction of MetalsMetals

4. Extraction of 4. Extraction of MetalsMetals

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carbon-lined steel vesselacts as cathode

CO2 bubbles

Al (l)Al2O3 (l)

Drawoff Al (l)

-

+

Cathode: Al+3 + 3e- Al (l)

Anode: 2 O-2 + C (s) CO2 (g) + 4e-

frompowersource

Al+3

O-2

O-2

Al+3

O-2

graphite anodes

e-

e-

The Hall ProcessCathode: 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.