1. KNOCKHARDY PUBLISHING
ELECTROLYSIS
Level 4 Chemistry
KNOCKHARDY PUBLISHING

2. 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.
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3. ELECTROLYSIS CONTENTS What is electrolysis?
Electrolysis of ionic compounds
Electrolysis of molten sodium chloride
Electrolysis of water

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

5. 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

6. 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

7. 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

8. 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

9. ELECTROLYSIS OF IONIC COMPOUNDS

10. CONDUCTING ELECTRICITY

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

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

13. 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

14. 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.

15. 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

16. 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

17. 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

18. 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

19. 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

20. ELECTROLYSIS OF MOLTEN SODIUM CHLORIDE

21. ELECTROLYSIS OF SODIUM CHLORIDE
DOWNS CELL

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

23. 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

24. 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

25. 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

26. 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- Cl e-

27. 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- Cl e-

28. 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- Cl e-

29. ELECTROLYSIS OF AQUEOUS SODIUM CHLORIDE (BRINE)

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

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

32. 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...

33. 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

34. 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...

35. 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

36. ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE
HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS
H e H

37. 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 e H2
The atoms form molecules and hydrogen gas H2 is produced

38. ELECTROLYSIS OF BRINE AT THE NEGATIVE CATHODE
HYDROGEN IONS PICK UP AN ELECTRON AND BECOME ATOMS
H e H
2H e H2
AT THE POSITIVE ANODE
CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS
Cl Cl + e-

39. 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 e H2
AT THE POSITIVE ANODE
CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS
Cl Cl + e-
2Cl- Cl e-
The atoms form molecules and chlorine gas Cl2 is produced

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

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

42. 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 e H2
AT THE POSITIVE ANODE
CHLORIDE IONS GIVE UP AN ELECTRON AND BECOME ATOMS
Cl Cl + e-
2Cl- Cl e-
SODIUM HYDROXIDE SOLUTION REMAINS

43. ELECTROLYSIS OF…
MOLTEN LEAD BROMIDE

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

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

46. ELECTROLYSIS OF…
DILUTE SULPHURIC ACID

47. ELECTROLYSIS OF…
DILUTE SULPHURIC ACID
SO42-
ANODE
CATHODE

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

49. 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 OH- 2H2O + O e- OXIDATION
CATHODE H e H2 REDUCTION

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

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

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

53. 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

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

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

56. 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 Cu e- OXIDATION
CATHODE Cu e- Cu REDUCTION

57. DILUTE HYDROCHLORIC ACID
ELECTROLYSIS OF…
DILUTE HYDROCHLORIC ACID

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

59. DILUTE HYDROCHLORIC ACID
ELECTROLYSIS OF…
DILUTE HYDROCHLORIC ACID H Cl Cl
Cl-
ANODE Cl- Cl e- OXIDATION
CATHODE H e- H2 REDUCTION

60. 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).

61. © 2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHING
ELECTROLYSIS
THE END
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