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ELECTROLYSISELECTROLYSISA guide for GCSE studentsA guide for GCSE students
2010 2010 SPECIFICATIONSSPECIFICATIONSKNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING
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ELECTROLYSISELECTROLYSIS
INTRODUCTION
This Powerpoint show is one of several produced to help students understand selected GCSE Chemistry topics. It is based on the requirements of the AQA specification but is suitable for other examination boards.
Individual students may use the material at home for revision purposes and it can also prove useful for classroom teaching with an interactive white board.
Accompanying notes on this, and the full range of AS and A2 Chemistry topics, are available from the KNOCKHARDY WEBSITE at...
www.knockhardy.org.uk
All diagrams, photographs and any animations in this Powerpoint are original and created by Jonathan Hopton. Permission must be obtained for their use in any work that is distributed for financial gain.
All diagrams, photographs and any animations in this Powerpoint are original and created by Jonathan Hopton. Permission must be obtained for their use in any work that is distributed for financial gain.
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CONTENTSCONTENTS
• What is electrolysis?
• Electrolysis of ionic compounds
• Electrolysis of molten sodium chloride
• Electrolysis of aqueous sodium chloride (brine)
• Diaphragm cell
• Electrolysis of aluminium oxide
• Other electrolytic systems
• Electrolysis of water
ELECTROLYSISELECTROLYSIS
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Passing an electric current through ionic substances that are Passing an electric current through ionic substances that are molten or in or in aqueous solution, breaks them down into elements. solution, breaks them down into elements.
ELECTROLYSISELECTROLYSIS
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Passing an electric current through ionic substances that are molten or in aqueous solution, breaks them down into elements.
The process is known as ELECTROLYSIS
ELECTROLYSISELECTROLYSIS
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Passing an electric current through ionic substances that are molten or in aqueous solution, breaks them down into elements.
The process is known as ELECTROLYSIS
The substance broken down is called the ELECTROLYTE
ELECTROLYSISELECTROLYSIS
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Passing an electric current through ionic substances that are molten or in aqueous solution, breaks them down into elements.
The process is known as ELECTROLYSIS
The substance broken down is called the ELECTROLYTE
During electrolysis…
Positively charged ions move to the negative electrode - CATHODE
Negatively charged ions move to the positive electrode - ANODE
ELECTROLYSISELECTROLYSIS
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Passing an electric current through ionic substances that are molten or in aqueous solution, breaks them down into elements.
The process is known as ELECTROLYSIS
The substance broken down is called the ELECTROLYTE
During electrolysis…
Positively charged ions move to the negative electrode - CATHODE
Negatively charged ions move to the positive electrode - ANODE
CATHODE +ive ions gain electrons REDUCTION
ANODE - ive ions give up (lose) electrons OXIDATION
ELECTROLYSISELECTROLYSIS
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ELECTROLYSIS OF ELECTROLYSIS OF IONIC COMPOUNDSIONIC COMPOUNDS
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CONDUCTING ELECTRICITYCONDUCTING ELECTRICITY
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For a substance to conduct electricity it must have either…
CONDUCTING ELECTRICITYCONDUCTING ELECTRICITY
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For a substance to conduct electricity it must have either…
electrons which are free to move about (metals / graphite)
CONDUCTING ELECTRICITYCONDUCTING ELECTRICITY
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For a substance to conduct electricity it must have either…
electrons which are free to move about (metals / graphite)
or ions which are free to move about
CONDUCTING ELECTRICITYCONDUCTING ELECTRICITY
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For a substance to conduct electricity it must have either…
electrons which are free to move about (metals / graphite)
or ions which are free to move about
When an ionic substance is melted or dissolved in water,the ions are free to move about within the liquid or solution.
CONDUCTING ELECTRICITYCONDUCTING ELECTRICITY
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ELECTROLYSIS OF IONIC COMPOUNDSELECTROLYSIS OF IONIC COMPOUNDS
Na+Cl- Na+Cl-
Na+Cl-Na+ Cl-
Na+Cl- Na+Cl-
WHEN SOLID, THE IONS ARE NOT FREE TO MOVE
NO CONDUCTIONOF ELECTRICITY
SOLID
SOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITYSOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITY
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ELECTROLYSIS OF IONIC COMPOUNDSELECTROLYSIS OF IONIC COMPOUNDS
Na+Cl- Na+Cl-
Na+Cl-Na+ Cl-
Na+Cl- Na+Cl-
WHEN SOLID, THE IONS ARE NOT FREE TO MOVE
NO CONDUCTIONOF ELECTRICITY
Na+ Cl-
Na+
Cl-
Na+
Cl-
Na+Cl-
SOLID MOLTEN
WHEN MOLTEN, THE IONS ARE FREE TO MOVE
ELECTRICITY IS CONDUCTED
MOLTEN IONIC COMPOUNDS DO CONDUCT ELECTRICITYMOLTEN IONIC COMPOUNDS DO CONDUCT ELECTRICITY
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ELECTROLYSIS OF IONIC COMPOUNDSELECTROLYSIS OF IONIC COMPOUNDS
Na+Cl- Na+Cl-
Na+Cl-Na+ Cl-
Na+Cl- Na+Cl-
WHEN SOLID, THE IONS ARE NOT FREE TO MOVE
NO CONDUCTIONOF ELECTRICITY
SOLID
SOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITYSOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITY
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ELECTROLYSIS OF IONIC COMPOUNDSELECTROLYSIS OF IONIC COMPOUNDS
Na+Cl- Na+Cl-
Na+Cl-Na+ Cl-
Na+Cl- Na+Cl-
WHEN SOLID, THE IONS ARE NOT FREE TO MOVE
NO CONDUCTIONOF ELECTRICITY
SOLID
AQUEOUS SOLUTIONS OF IONIC COMPOUNDS DO CONDUCT ELECTRICITYAQUEOUS SOLUTIONS OF IONIC COMPOUNDS DO CONDUCT ELECTRICITY
Add to water
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ELECTROLYSIS OF IONIC COMPOUNDSELECTROLYSIS OF IONIC COMPOUNDS
Na+Cl- Na+Cl-
Na+Cl-Na+ Cl-
Na+Cl- Na+Cl-
WHEN SOLID, THE IONS ARE NOT FREE TO MOVE
NO CONDUCTIONOF ELECTRICITY
Na+ Cl-
Na+
Cl-
Na+
Cl-
Na+Cl-
SOLID IN AQUEOUS SOLUTION
WHEN DISSOLVED IN WATER, THE IONS ARE
FREE TO MOVE
ELECTRICITY IS CONDUCTED
AQUEOUS SOLUTIONS OF IONIC COMPOUNDS DO CONDUCT ELECTRICITYAQUEOUS SOLUTIONS OF IONIC COMPOUNDS DO CONDUCT ELECTRICITY
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ELECTROLYSIS OF ELECTROLYSIS OF MOLTEN SODIUM MOLTEN SODIUM
CHLORIDECHLORIDE
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ELECTROLYSIS OF SODIUM CHLORIDEELECTROLYSIS OF SODIUM CHLORIDE
DOWNS CELLDOWNS CELL
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ELECTROLYSIS OF SODIUM CHLORIDEELECTROLYSIS OF SODIUM CHLORIDE
SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES
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ELECTROLYSIS OF SODIUM CHLORIDEELECTROLYSIS OF SODIUM CHLORIDE
SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES
WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE
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ELECTROLYSIS OF SODIUM CHLORIDEELECTROLYSIS OF SODIUM CHLORIDE
SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES
WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE
SODIUM IONS GO TO THE CATHODE AND EACH PICK UP AN ELECTRON
Na+ + e- Na
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ELECTROLYSIS OF SODIUM CHLORIDEELECTROLYSIS OF SODIUM CHLORIDE
SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES
WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE
SODIUM IONS GO TO THE CATHODE AND EACH PICK UP AN ELECTRON
Na+ + e- Na
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ELECTROLYSIS OF SODIUM CHLORIDEELECTROLYSIS OF SODIUM CHLORIDE
SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES
WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE
SODIUM IONS GO TO THE CATHODE AND EACH PICK UP AN ELECTRON
Na+ + e- Na
CHLORIDE IONS GO TO THE ANODE AND EACH GIVE UP AN ELECTRON
Cl- Cl + e-
2Cl- Cl2 + 2e-
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ELECTROLYSIS OF SODIUM CHLORIDEELECTROLYSIS OF SODIUM CHLORIDE
SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES
WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE
SODIUM IONS GO TO THE CATHODE AND EACH PICK UP AN ELECTRON
Na+ + e- Na
CHLORIDE IONS GO TO THE ANODE AND EACH GIVE UP AN ELECTRON
Cl- Cl + e-
2Cl- Cl2 + 2e-
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ELECTROLYSIS OF SODIUM CHLORIDEELECTROLYSIS OF SODIUM CHLORIDE
SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES
WHEN MOLTEN, THE IONS HAVE MORE FREEDOM AND CAN MOVE
SODIUM IONS GO TO THE CATHODE AND EACH PICK UP AN ELECTRON
Na+ + e- Na
CHLORIDE IONS GO TO THE ANODE AND EACH GIVE UP AN ELECTRON
Cl- Cl + e-
2Cl- Cl2 + 2e-
SUMMARY
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ELECTROLYSIS OF ELECTROLYSIS OF AQUEOUS SODIUM AQUEOUS SODIUM CHLORIDE CHLORIDE (BRINE)(BRINE)
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE
WATER CONTAINS A FEW IONS
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE
WATER CONTAINS A FEW IONS
POSITIVE IONS ARE ATTRACTED TO THE NEGATIVE CATHODE...
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE
WATER CONTAINS A FEW IONS
POSITIVE IONS ARE ATTRACTED TO THE NEGATIVE CATHODE...OF THE TWO, HYDROGEN IONS ARE PREFERRED
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE
WATER CONTAINS A FEW IONS
POSITIVE IONS ARE ATTRACTED TO THE NEGATIVE CATHODE...OF THE TWO, HYDROGEN IONS ARE PREFERRED
NEGATIVE IONS ARE ATTRACTED TO THE POSITIVE ANODE...
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE
WATER CONTAINS A FEW IONS
POSITIVE IONS ARE ATTRACTED TO THE NEGATIVE CATHODE...OF THE TWO, HYDROGEN IONS ARE PREFERRED
NEGATIVE IONS ARE ATTRACTED TO THE POSITIVE ANODE...OF THE TWO, CHLORIDE IONS ARE PREFERRED
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
AT THE NEGATIVE CATHODEHYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS
H+ + e- H
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
AT THE NEGATIVE CATHODEHYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS
H+ + e- H
2H+ + 2e- H2
The atoms form molecules and hydrogen gas H2 is produced
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
AT THE NEGATIVE CATHODEHYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS
H+ + e- H
2H+ + 2e- H2
AT THE POSITIVE ANODECHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS
Cl- Cl + e-
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
AT THE NEGATIVE CATHODEHYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS
H+ + e- H
2H+ + 2e- H2
AT THE POSITIVE ANODECHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS
Cl- Cl + e-
2Cl- Cl2 + 2e-
The atoms form molecules and chlorine gas Cl2 is produced
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
SODIUM HYDROXIDE SOLUTION REMAINS
AT THE NEGATIVE CATHODEHYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS
H+ + e- H
2H+ + 2e- H2
AT THE POSITIVE ANODECHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS
Cl- Cl + e-
2Cl- Cl2 + 2e-
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
SODIUM HYDROXIDE SOLUTION REMAINS
AT THE NEGATIVE CATHODEHYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS
H+ + e- H
2H+ + 2e- H2
AT THE POSITIVE ANODECHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS
Cl- Cl + e-
2Cl- Cl2 + 2e-
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ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
AT THE NEGATIVE CATHODEHYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS
H+ + e- H
2H+ + 2e- H2
AT THE POSITIVE ANODECHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS
Cl- Cl + e-
2Cl- Cl2 + 2e- SODIUM HYDROXIDE SOLUTION REMAINS
SUMMARY
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INDUSTRIAL INDUSTRIAL ELECTROLYSISELECTROLYSIS
OF BRINEOF BRINE
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SODIUM CHLORIDESODIUM CHLORIDE
CHLORINE GAS
THE DIAPHRAGM CELL
HYDROGEN GAS
BRINE
SODIUM HYDROXIDESOLUTION(CAUSTIC SODA)
DIAPHRAGMSTOPS CHLORINE MIXING WITH SODIUM HYDROXIDE
IONS
IONS
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THE DIAPHRAGM CELLTHE DIAPHRAGM CELL
IMPORTANT ASPECTS
WHAT IS AN ADVANTAGE OF ELECTROLYSING BRINE RATHER THAN MOLTEN
SODIUM CHLORIDE?
WHAT IS AN ADVANTAGE OF ELECTROLYSING BRINE RATHER THAN MOLTEN
SODIUM CHLORIDE?
CHLORINE HYDROGEN
BRINE
SODIUMHYDROXIDE(CAUSTIC SODA)
DIAPHRAGM
IONS
IONS
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THE DIAPHRAGM CELLTHE DIAPHRAGM CELL
IMPORTANT ASPECTS
WHAT IS AN ADVANTAGE OF ELECTROLYSING BRINE RATHER THAN MOLTEN
SODIUM CHLORIDE?
WHAT IS AN ADVANTAGE OF ELECTROLYSING BRINE RATHER THAN MOLTEN
SODIUM CHLORIDE?
CHLORINE HYDROGEN
BRINE
SODIUMHYDROXIDE(CAUSTIC SODA)
DIAPHRAGM
IONS
IONS
LESS ENERGY IS NEEDED BECAUSE YOU DON’T HAVE TO MELT THE SODIUM CHLORIDE; IT HAS A HIGH MELTING POINT
LESS ENERGY IS NEEDED BECAUSE YOU DON’T HAVE TO MELT THE SODIUM CHLORIDE; IT HAS A HIGH MELTING POINT
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THE DIAPHRAGM CELLTHE DIAPHRAGM CELL
IMPORTANT ASPECTS
WHAT HAPPENS AT THE POSITIVE ANODE?
WHAT HAPPENS AT THE POSITIVE ANODE?
CHLORINE HYDROGEN
BRINE
SODIUMHYDROXIDE(CAUSTIC SODA)
DIAPHRAGM
IONS
IONS
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THE DIAPHRAGM CELLTHE DIAPHRAGM CELL
IMPORTANT ASPECTS
WHAT HAPPENS AT THE POSITIVE ANODE?
WHAT HAPPENS AT THE POSITIVE ANODE?
CHLORINE HYDROGEN
BRINE
SODIUMHYDROXIDE(CAUSTIC SODA)
DIAPHRAGM
IONS
IONS
CHLORIDE IONS ARE OXIDISED
Cl¯ – e¯ Cl
2Cl¯ – 2e¯ Cl2
CHLORIDE IONS ARE OXIDISED
Cl¯ – e¯ Cl
2Cl¯ – 2e¯ Cl2
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THE DIAPHRAGM CELLTHE DIAPHRAGM CELL
IMPORTANT ASPECTS
WHAT HAPPENS AT THENEGATIVE CATHODE?
WHAT HAPPENS AT THENEGATIVE CATHODE?
CHLORINE HYDROGEN
BRINE
SODIUMHYDROXIDE(CAUSTIC SODA)
DIAPHRAGM
IONS
IONS
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THE DIAPHRAGM CELLTHE DIAPHRAGM CELL
IMPORTANT ASPECTS
WHAT HAPPENS AT THENEGATIVE CATHODE?
WHAT HAPPENS AT THENEGATIVE CATHODE?
CHLORINE HYDROGEN
BRINE
SODIUMHYDROXIDE(CAUSTIC SODA)
DIAPHRAGM
IONS
IONS
HYDROGEN IONS ARE REDUCED
H+ + e¯ H
2H+ + 2e¯ H2
HYDROGEN IONS ARE REDUCED
H+ + e¯ H
2H+ + 2e¯ H2
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THE DIAPHRAGM CELLTHE DIAPHRAGM CELL
IMPORTANT ASPECTS
WHAT IS THEDIAPHRAGM FOR?
WHAT IS THEDIAPHRAGM FOR?
CHLORINE HYDROGEN
BRINE
SODIUMHYDROXIDE(CAUSTIC SODA)
DIAPHRAGM
IONS
IONS
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THE DIAPHRAGM CELLTHE DIAPHRAGM CELL
IMPORTANT ASPECTS
WHAT IS THEDIAPHRAGM FOR?
WHAT IS THEDIAPHRAGM FOR?
CHLORINE HYDROGEN
BRINE
SODIUMHYDROXIDE(CAUSTIC SODA)
DIAPHRAGM
IONS
IONS
PREVENTS CHLORINE COMING INTO CONTACT WITH ANY SODIUM
HYDROXIDE
PREVENTS CHLORINE COMING INTO CONTACT WITH ANY SODIUM
HYDROXIDE
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THE DIAPHRAGM CELLTHE DIAPHRAGM CELL
IMPORTANT ASPECTS
WHAT IS ALSOPRODUCED?
WHAT IS ALSOPRODUCED?
CHLORINE HYDROGEN
BRINE
SODIUMHYDROXIDE(CAUSTIC SODA)
DIAPHRAGM
IONS
IONS
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THE DIAPHRAGM CELLTHE DIAPHRAGM CELL
IMPORTANT ASPECTS
WHAT IS ALSOPRODUCED?
WHAT IS ALSOPRODUCED?
CHLORINE HYDROGEN
BRINE
SODIUMHYDROXIDE(CAUSTIC SODA)
DIAPHRAGM
IONS
IONS
THE SOLUTION CONTAINS SODIUM IONS AND HYDROXIDE IONS SO
SODIUM HYDROXIDE IS PRODUCED
THE SOLUTION CONTAINS SODIUM IONS AND HYDROXIDE IONS SO
SODIUM HYDROXIDE IS PRODUCED
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THE DIAPHRAGM CELLTHE DIAPHRAGM CELL
INDUSTRIAL IMPORTANCE
The products of the electrolysis of brine are of great industrial importance…
CHLORINE making bleachmaking plastics such as pvc
HYDROGEN used as fuelused in margarine production
SODIUM production of soaps and detergents HYDROXIDE used in the paper industry
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EXTRACTION OF EXTRACTION OF ALUMINIUM BY ALUMINIUM BY ELECTROLYSISELECTROLYSIS
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
ELECTROLYSISELECTROLYSIS
Unlike iron, aluminium cannot be extracted using carbon.(Aluminium is above carbon in the reactivity series)
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
ELECTROLYSISELECTROLYSIS
Unlike iron, aluminium cannot be extracted using carbon.(Aluminium is above carbon in the reactivity series)
Reactive metals are extracted using electrolysis
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
ELECTROLYSISELECTROLYSIS
Unlike iron, aluminium cannot be extracted using carbon.(Aluminium is above carbon in the reactivity series)
Reactive metals are extracted using electrolysis
Electrolysis is expensive - it requires a lot of energy…
- ore must be molten (ores have high melting points)
- electricity is needed for the electrolysis process
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
RAW MATERIALSRAW MATERIALS
BAUXITE aluminium ore
Bauxite contains alumina (Al2O3 aluminium oxide) plus impurities such as iron oxide – it is purified before use.
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
RAW MATERIALSRAW MATERIALS
BAUXITE aluminium ore
Bauxite contains alumina (Al2O3 aluminium oxide) plus impurities such as iron oxide – it is purified before use.
CRYOLITE Aluminium oxide has a veryhigh melting point.Adding cryolite lowers the
melting point and saves energy.
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
THE CELL CONSISTS OF A
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
CARBON ANODE
THE CELL CONSISTS OF A CARBON ANODE
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
STEEL CATHODE
CARBON LINING
THE CELL CONSISTS OF A CARBON LINED STEEL CATHODE
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
MOLTEN ALUMINA and
CRYOLITE
ALUMINA IS DISSOLVED IN MOLTEN CRYOLITE Na3AlF6
SAVES ENERGY - the mixture melts at a lower temperature
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
MOLTEN ALUMINA and
CRYOLITE
ALUMINA IS DISSOLVED IN MOLTEN CRYOLITE Na3AlF6
aluminium and oxide ions are now free to move
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
POSITIVE ALUMINIUM IONS ARE ATTRACTED
TO THE NEGATIVE CATHODE
Al3+ + 3e- Al
EACH ION PICKS UP 3 ELECTRONS AND IS DISCHARGED
CARBON CATHODE
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O2- O + 2e-
EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
NEGATIVE OXIDE IONS ARE
ATTRACTED TO THE POSITIVE
ANODE
EACH ION GIVES UP 2 ELECTRONS AND IS DISCHARGED
CARBON ANODE
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
ELECTRONS
CARBON ANODE
CARBON CATHODE
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
ELECTRONS
ANODE 3O2- 1½O2 + 6e- OXIDATION
OXIDATION (LOSS OF ELECTRONS) TAKES PLACE
AT THE ANODECARBON ANODE
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
ELECTRONS
CATHODE 2Al3+ + 6e- 2Al REDUCTION
OXIDATION (LOSS OF ELECTRONS) TAKES PLACE
AT THE ANODE
REDUCTION (GAIN OF ELECTRONS) TAKES PLACE AT
THE CATHODE CARBON CATHODE
ANODE 3O2- 1½O2 + 6e- OXIDATION
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
ELECTRONSOXIDATION (LOSS OF
ELECTRONS) TAKES PLACE AT THE ANODE
REDUCTION (GAIN OF ELECTRONS) TAKES PLACE AT
THE CATHODE
CARBON ANODE
CARBON CATHODE
ANODE 3O2- 1½O2 + 6e- OXIDATION
CATHODE 2Al3+ + 6e- 2Al REDUCTION
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
CARBON ANODE
PROBLEMTHE CARBON
ANODES REACT WITH THE
OXYGEN TO PRODUCE
CARBON DIOXIDE
CARBON DIOXIDE
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EXTRACTION OF ALUMINIUMEXTRACTION OF ALUMINIUM
CARBON ANODE
PROBLEMTHE CARBON
ANODES REACT WITH THE
OXYGEN TO PRODUCE
CARBON DIOXIDE
THE ANODES HAVE TO BE REPLACED AT REGULAR INTERVALS, THUS ADDING TO THE
COST OF THE EXTRACTION PROCESS
CARBON DIOXIDE
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USES OF ALUMINIUMUSES OF ALUMINIUM
THE IMPORTANCE OF ALUMINIUM
LOW DENSITY AND OVERHEAD CABLESELECTRICAL CONDUCTIVITY
LOW DENSITY AIRCRAFT BODIESneeds to be an alloyed withother metals for extra strength
GOOD HEAT CONDUCTIVITY SAUCEPANS
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USES OF ALUMINIUMUSES OF ALUMINIUM
THE IMPORTANCE OF ALUMINIUM
LOW DENSITY AND OVERHEAD CABLESELECTRICAL CONDUCTIVITY
LOW DENSITY AIRCRAFT BODIESneeds to be an alloyed withother metals for extra strength
GOOD HEAT CONDUCTIVITY SAUCEPANS
Aluminium is not as reactive as one would predict from its position in the reactivity series.
This is because a thin layer of oxide quickly forms on the surface and prevents any further reaction taking place.
THIN LAYER OF OXIDE
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USES OF ALUMINIUMUSES OF ALUMINIUM
THE IMPORTANCE OF ALUMINIUM
LOW DENSITY AND OVERHEAD CABLESELECTRICAL CONDUCTIVITY
LOW DENSITY AIRCRAFT BODIESneeds to be an alloyed withother metals for extra strength
GOOD HEAT CONDUCTIVITY SAUCEPANS
Aluminium is not as reactive as one would predict from its position in the reactivity series.
This is because a thin layer of oxide quickly forms on the surface and prevents any further reaction taking place.
ANODISING puts on a controlled layer of oxide so the metal can be used for household items such as pans and electrical goods.
THIN LAYER OF OXIDE
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USES OF ALUMINIUMUSES OF ALUMINIUM
ANODISING
This puts on a controlled layer of oxide so that the metal can be used for household items such as pans and electrical goods.
The aluminium object is made the anode in the electrolysis of dilute sulphuric acid.
Oxygen given of at the anode reacts with the aluminium surface, to build up a very thin film of oxide.
+ -
aluminium object to be
anodised
dilute sulphuric
acid
cathode
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ELECTROLYSIS OF…ELECTROLYSIS OF…
MOLTEN LEAD BROMIDE
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ELECTROLYSIS OF…ELECTROLYSIS OF…
MOLTEN LEAD BROMIDE
Br-Br-
Pb2+
CATHODE
ANODE
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ELECTROLYSIS OF…ELECTROLYSIS OF…
MOLTEN LEAD BROMIDE
Br-Br-
Br Br
Pb2+
Pb
CATHODE Pb2+ + 2e- Pb REDUCTION
ANODE 2Br- Br2 + 2e- OXIDATION
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ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE SULPHURIC ACID
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ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE SULPHURIC ACID
SO42-
CATHODE
ANODE
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ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE SULPHURIC ACID
SO42-
CATHODE 4H+ + 4e- 2H2 REDUCTION
ANODE 4OH- 2H2O + O2 + 4e- OXIDATION
OO
H H
H H
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ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE SULPHURIC ACID
SO42-
CATHODE 4H+ + 4e- 2H2 REDUCTION
ANODE 4OH- 2H2O + O2 + 4e- OXIDATION
OO
H H
H H
This electrolysis can be used to
deduce the formula of water
This electrolysis can be used to
deduce the formula of water
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ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with carbon electrodes)
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ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with carbon electrodes)
Cu2+
SO42-
CATHODE
ANODE
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ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with carbon electrodes)
Cu2+
SO42-
CATHODE 2Cu2+ + 4e- 2Cu REDUCTION
ANODE 4OH- 2H2O + O2 + 4e- OXIDATION
OOCu
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ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with copper anode)
A different reaction takes place if the anode
is made of copper
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ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with copper anode)
Cu2+
SO42-
CATHODE
ANODE
Cu
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ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with copper anode)
Cu2+
SO42-
CATHODE Cu2+ + 2e- Cu REDUCTION
ANODE Cu Cu2+ + 2e- OXIDATION
Cu
Cu
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ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with copper anode)
Cu2+
SO42-
CATHODE Cu2+ + 2e- Cu REDUCTION
ANODE Cu Cu2+ + 2e- OXIDATION
Cu
Cu
This electrolysis can be used to
purify copper or copper plate
objects
This electrolysis can be used to
purify copper or copper plate
objects
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ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE HYDROCHLORIC ACID
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ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE HYDROCHLORIC ACID
CATHODE
ANODE
Cl-
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ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE HYDROCHLORIC ACID
CATHODE 2H+ + 2e- H2 REDUCTION
ANODE 2Cl- Cl2 + 2e- OXIDATION
H H
Cl-
Cl Cl
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COMPOSITION OF WATERCOMPOSITION OF WATER
WATER IS AN EXTREMELY POOR CONDUCTOR OFELECTRICITY. Dilute sulphuric acid must be added toimprove Its conductivity.
Fill both limbs of a Hoffman Voltameter with water, (acidified with a small amount of dilute sulphuric acid).Pass a direct current through the apparatus.
ANODE (+) - a colourless gas collected - the gas re-lit a glowing splint
CATHODE (-) - a colourless gas collected - its volume was twice that at anode- gas exploded with a squeaky pop when a lighted splint was applied
Conclusion Water can be split into its elementsby passing electricity through it.
water ——> hydrogen (2 vols) + oxygen (1 vol).
HOFFMANVOLTAMETER
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© 2011 © 2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHINGJONATHAN HOPTON & KNOCKHARDY PUBLISHING
ELECTROLYSISELECTROLYSIS
THE ENDTHE END