electrolysis level 4 chemistry knockhardy publishing

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