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ELECTROLYSISELECTROLYSISLevel 4 ChemistryLevel 4 Chemistry
KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING
ELECTROLYSISELECTROLYSIS
INTRODUCTION
This Powerpoint show is one of several produced to help students understand selected National 4 Chemistry topics. It is based on the requirements of the SQA specification.
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 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.
CONTENTSCONTENTS
• What is electrolysis?
• Electrolysis of ionic compounds
• Electrolysis of molten sodium chloride
• Electrolysis of water
ELECTROLYSISELECTROLYSIS
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
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
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
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
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
ELECTROLYSIS OF ELECTROLYSIS OF IONIC COMPOUNDSIONIC COMPOUNDS
CONDUCTING ELECTRICITYCONDUCTING ELECTRICITY
For a substance to conduct electricity it must have either…
CONDUCTING ELECTRICITYCONDUCTING ELECTRICITY
For a substance to conduct electricity it must have either…
electrons which are free to move about (metals / graphite)
CONDUCTING ELECTRICITYCONDUCTING ELECTRICITY
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
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
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
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
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
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
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
ELECTROLYSIS OF ELECTROLYSIS OF MOLTEN SODIUM MOLTEN SODIUM
CHLORIDECHLORIDE
ELECTROLYSIS OF SODIUM CHLORIDEELECTROLYSIS OF SODIUM CHLORIDE
DOWNS CELLDOWNS CELL
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
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
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
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
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-
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-
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
ELECTROLYSIS OF ELECTROLYSIS OF AQUEOUS SODIUM AQUEOUS SODIUM CHLORIDE CHLORIDE (BRINE)(BRINE)
ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE
ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE
WATER CONTAINS A FEW IONS
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...
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
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...
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
ELECTROLYSIS OF BRINEELECTROLYSIS OF BRINE
AT THE NEGATIVE CATHODEHYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS
H+ + e- H
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
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-
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
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-
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-
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
ELECTROLYSIS OF…ELECTROLYSIS OF…
MOLTEN LEAD BROMIDE
ELECTROLYSIS OF…ELECTROLYSIS OF…
MOLTEN LEAD BROMIDE
Br-Br-
Pb2+
CATHODE
ANODE
ELECTROLYSIS OF…ELECTROLYSIS OF…
MOLTEN LEAD BROMIDE
Br-Br-
Br Br
Pb2+
Pb
CATHODE Pb2+ + 2e- Pb REDUCTION
ANODE 2Br- Br2 + 2e- OXIDATION
ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE SULPHURIC ACID
ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE SULPHURIC ACID
SO42-
CATHODE
ANODE
ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE SULPHURIC ACID
SO42-
CATHODE 4H+ + 4e- 2H2 REDUCTION
ANODE 4OH- 2H2O + O2 + 4e- OXIDATION
OO
H H
H H
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
ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with carbon electrodes)
ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with carbon electrodes)
Cu2+
SO42-
CATHODE
ANODE
ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with carbon electrodes)
Cu2+
SO42-
CATHODE 2Cu2+ + 4e- 2Cu REDUCTION
ANODE 4OH- 2H2O + O2 + 4e- OXIDATION
OOCu
ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with copper anode)
A different reaction takes place if the anode
is made of copper
ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with copper anode)
Cu2+
SO42-
CATHODE
ANODE
Cu
ELECTROLYSIS OF…ELECTROLYSIS OF…
AQUEOUS COPPER SULPHATE (with copper anode)
Cu2+
SO42-
CATHODE Cu2+ + 2e- Cu REDUCTION
ANODE Cu Cu2+ + 2e- OXIDATION
Cu
Cu
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
ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE HYDROCHLORIC ACID
ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE HYDROCHLORIC ACID
CATHODE
ANODE
Cl-
ELECTROLYSIS OF…ELECTROLYSIS OF…
DILUTE HYDROCHLORIC ACID
CATHODE 2H+ + 2e- H2 REDUCTION
ANODE 2Cl- Cl2 + 2e- OXIDATION
H H
Cl-
Cl Cl
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
© 2011 © 2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHINGJONATHAN HOPTON & KNOCKHARDY PUBLISHING
ELECTROLYSISELECTROLYSIS
THE ENDTHE END
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