KNOCKHARDY PUBLISHING ELECTROLYSIS Level 4 Chemistry KNOCKHARDY PUBLISHING

ELECTROLYSIS INTRODUCTION www.knockhardy.org.uk 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.

ELECTROLYSIS CONTENTS What is electrolysis? Electrolysis of ionic compounds Electrolysis of molten sodium chloride Electrolysis of water

ELECTROLYSIS Passing an electric current through ionic substances that are molten or in aqueous solution, breaks them down into elements.

ELECTROLYSIS 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

ELECTROLYSIS 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

ELECTROLYSIS During electrolysis… 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

ELECTROLYSIS During electrolysis… 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

ELECTROLYSIS OF IONIC COMPOUNDS

CONDUCTING ELECTRICITY

CONDUCTING ELECTRICITY For a substance to conduct electricity it must have either…

CONDUCTING ELECTRICITY For a substance to conduct electricity it must have either… electrons which are free to move about (metals / graphite)

CONDUCTING 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 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.

ELECTROLYSIS OF IONIC COMPOUNDS SOLID Na+ Cl- WHEN SOLID, THE IONS ARE NOT FREE TO MOVE NO CONDUCTION OF ELECTRICITY SOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITY

ELECTROLYSIS OF IONIC COMPOUNDS SOLID MOLTEN Na+ Cl- Cl- Na+ Na+ Cl- Cl- Cl- Na+ Na+ WHEN SOLID, THE IONS ARE NOT FREE TO MOVE NO CONDUCTION OF ELECTRICITY WHEN MOLTEN, THE IONS ARE FREE TO MOVE ELECTRICITY IS CONDUCTED MOLTEN IONIC COMPOUNDS DO CONDUCT ELECTRICITY

ELECTROLYSIS OF IONIC COMPOUNDS SOLID Na+ Cl- WHEN SOLID, THE IONS ARE NOT FREE TO MOVE NO CONDUCTION OF ELECTRICITY SOLID IONIC COMPOUNDS DON’T CONDUCT ELECTRICITY

ELECTROLYSIS OF IONIC COMPOUNDS SOLID Na+ Cl- Add to water WHEN SOLID, THE IONS ARE NOT FREE TO MOVE NO CONDUCTION OF ELECTRICITY AQUEOUS SOLUTIONS OF IONIC COMPOUNDS DO CONDUCT ELECTRICITY

ELECTROLYSIS OF IONIC COMPOUNDS SOLID IN AQUEOUS SOLUTION Na+ Cl- Cl- Na+ Na+ Cl- Cl- Cl- Na+ Na+ WHEN SOLID, THE IONS ARE NOT FREE TO MOVE NO CONDUCTION OF ELECTRICITY WHEN DISSOLVED IN WATER, THE IONS ARE FREE TO MOVE ELECTRICITY IS CONDUCTED AQUEOUS SOLUTIONS OF IONIC COMPOUNDS DO CONDUCT ELECTRICITY

ELECTROLYSIS OF MOLTEN SODIUM CHLORIDE

ELECTROLYSIS OF SODIUM CHLORIDE DOWNS CELL

ELECTROLYSIS OF SODIUM CHLORIDE SOLID SODIUM CHLORIDE DOES NOT CONDUCT ELECTRICITY BECAUSE THE IONS ARE NOT FREE TO MOVE TO THE ELECTRODES

ELECTROLYSIS 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 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 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 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 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 CHLORIDE SUMMARY 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 AQUEOUS SODIUM CHLORIDE (BRINE)

ELECTROLYSIS OF BRINE WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE

ELECTROLYSIS OF BRINE WHEN SODIUM CHLORIDE DISSOLVES IN WATER, THE IONS SEPARATE WATER CONTAINS A FEW IONS

ELECTROLYSIS 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 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 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 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 BRINE AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H

The atoms form molecules and hydrogen gas H2 is produced ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE HYDROGEN 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 BRINE AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H 2H+ + 2e- H2 AT THE POSITIVE ANODE CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS Cl- Cl + e-

The atoms form molecules and chlorine gas Cl2 is produced ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H 2H+ + 2e- H2 AT THE POSITIVE ANODE CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS Cl- Cl + e- 2Cl- Cl2 + 2e- The atoms form molecules and chlorine gas Cl2 is produced

SODIUM HYDROXIDE SOLUTION REMAINS ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H 2H+ + 2e- H2 AT THE POSITIVE ANODE CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS Cl- Cl + e- 2Cl- Cl2 + 2e- SODIUM HYDROXIDE SOLUTION REMAINS

SODIUM HYDROXIDE SOLUTION REMAINS ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H 2H+ + 2e- H2 AT THE POSITIVE ANODE CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS Cl- Cl + e- 2Cl- Cl2 + 2e- SODIUM HYDROXIDE SOLUTION REMAINS

SODIUM HYDROXIDE SOLUTION REMAINS ELECTROLYSIS OF BRINE SUMMARY AT THE NEGATIVE CATHODE HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS H+ + e- H 2H+ + 2e- H2 AT THE POSITIVE ANODE CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS Cl- Cl + e- 2Cl- Cl2 + 2e- SODIUM HYDROXIDE SOLUTION REMAINS

ELECTROLYSIS OF… MOLTEN LEAD BROMIDE

ELECTROLYSIS OF… MOLTEN LEAD BROMIDE Pb2+ Br- Br- ANODE CATHODE

ELECTROLYSIS OF… Pb Pb2+ Br Br- Br- ANODE 2Br- Br2 + 2e- OXIDATION MOLTEN LEAD BROMIDE Br Pb Pb2+ Br- Br- ANODE 2Br- Br2 + 2e- OXIDATION CATHODE Pb2+ + 2e- Pb REDUCTION

ELECTROLYSIS OF… DILUTE SULPHURIC ACID

ELECTROLYSIS OF… DILUTE SULPHURIC ACID SO42- ANODE CATHODE

ELECTROLYSIS OF… O SO42- ANODE 4OH- 2H2O + O2 + 4e- OXIDATION DILUTE SULPHURIC ACID O H H SO42- ANODE 4OH- 2H2O + O2 + 4e- OXIDATION CATHODE 4H+ + 4e- 2H2 REDUCTION

This electrolysis can be used to deduce the formula of water ELECTROLYSIS OF… DILUTE SULPHURIC ACID O H H SO42- This electrolysis can be used to deduce the formula of water ANODE 4OH- 2H2O + O2 + 4e- OXIDATION CATHODE 4H+ + 4e- 2H2 REDUCTION

AQUEOUS COPPER SULPHATE (with carbon electrodes) ELECTROLYSIS OF… AQUEOUS COPPER SULPHATE (with carbon electrodes)

AQUEOUS COPPER SULPHATE (with carbon electrodes) ELECTROLYSIS OF… AQUEOUS COPPER SULPHATE (with carbon electrodes) SO42- Cu2+ ANODE CATHODE

AQUEOUS COPPER SULPHATE (with carbon electrodes) ELECTROLYSIS OF… AQUEOUS COPPER SULPHATE (with carbon electrodes) O Cu SO42- Cu2+ ANODE 4OH- 2H2O + O2 + 4e- OXIDATION CATHODE 2Cu2+ + 4e- 2Cu REDUCTION

A different reaction takes place if the anode is made of copper ELECTROLYSIS OF… AQUEOUS COPPER SULPHATE (with copper anode) A different reaction takes place if the anode is made of copper

AQUEOUS COPPER SULPHATE (with copper anode) ELECTROLYSIS OF… AQUEOUS COPPER SULPHATE (with copper anode) SO42- Cu Cu2+ ANODE CATHODE

AQUEOUS COPPER SULPHATE (with copper anode) ELECTROLYSIS OF… AQUEOUS COPPER SULPHATE (with copper anode) Cu SO42- Cu Cu2+ ANODE Cu Cu2+ + 2e- OXIDATION CATHODE Cu2+ + 2e- Cu REDUCTION

ELECTROLYSIS OF… AQUEOUS COPPER SULPHATE (with copper anode) Cu SO42- Cu Cu2+ This electrolysis can be used to purify copper or copper plate objects ANODE Cu Cu2+ + 2e- OXIDATION CATHODE Cu2+ + 2e- Cu REDUCTION

DILUTE HYDROCHLORIC ACID ELECTROLYSIS OF… DILUTE HYDROCHLORIC ACID

DILUTE HYDROCHLORIC ACID ELECTROLYSIS OF… DILUTE HYDROCHLORIC ACID Cl- ANODE CATHODE

DILUTE HYDROCHLORIC ACID ELECTROLYSIS OF… DILUTE HYDROCHLORIC ACID H Cl Cl Cl- ANODE 2Cl- Cl2 + 2e- OXIDATION CATHODE 2H+ + 2e- H2 REDUCTION

water ——> hydrogen (2 vols) + oxygen (1 vol). COMPOSITION OF WATER WATER IS AN EXTREMELY POOR CONDUCTOR OF ELECTRICITY. Dilute sulphuric acid must be added to improve 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 elements by passing electricity through it. HOFFMAN VOLTAMETER water ——> hydrogen (2 vols) + oxygen (1 vol).

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