2. PRESENTER MS FARZANA MEHBOOB Head of the Science department
D.A.Neelum high school

3. INSTRUCTIONAL LESSON
ELECTROLYSIS

4. TOPIC:
Electrolysis &
its
Application

5. Division of lesson
Qualitative Aspect of Electrolysis
Quantitative Aspect of Electrolysis

6. LEARNING OBJECTIVES (Low order thinking)
What is electrolysis?
Terminologies use in electrolysis
Differences between a galvanic cell and electrolytic cell
Electrolysis mechanism
The equations of the reactions take place at electrodes
The various applications of electrolysis with examples

7. BLOOM BASED OBJECTIVES
(Highorder thinking)
Use a Venn diagram to show how electrolytic cell and electrochemical cell are similar and different.
ANALYSING
Conduct an experiment to check whether sodium chloride can act as an electrolyte in solid state or can not. Give reason.

8. BLOOM BASED OBJECTIVES (Highorder thinking)
Form a panel to discuss the influence of electrolysis on our lives.
EVALUATING
State one advantage of Down process from a pollution point of view and also one commercial advantage.

9. BLOOM BASED OBJECTIVES (Highorder thinking)
Suggest how could the experiment be changed to avoid the formation of poisonous fumes of chlorine gas in the given experiment.
CREATING
Investigate what economic and environmental issues might influence the siting of the purification plant during the purification of copper on the large scale. Make a PPt presentation..

10. Electrolysis Humphry Davy 1778-1829. Prepared metallic K, Na, Sr,
Ca, B, Ba, Mg, Li by electrolysis. 1 1 1 1

11. electricity Break apart Electrolysis Electro lysis
WHAT IS ELECTROLYSIS
Electrolysis
Latin word
Electro
electricity
and
lysis
Break apart
through

12. in chemical reactions at the electrodes and separation of materials.
through resulting
DEFINITION
Electrolysis is the passage of an electric current
A Polar compound that is either molten or dissolved in a suitable solvent,
in chemical reactions at the electrodes and separation of materials.

13. GENERAL TERMS USED IN ELECTROLYSIS
Electrolytic cell
It has three component parts:
An electrolyte
Two electrodes (a cathode and an anode).
A battery

14. ELECTROLYTES
substance that conducts electric current a result of a dissociation into positively and negatively ions in solution or molten form.
Examples:
Molten salts
Solution of salts in water
Solution of acids
Solutions of alkalis

15. TYPES OF ELECTROLYTE

16. ELECTRICAL CONDUCTIVITY Metallic conductivity Electron flow
Is of two types
Metallic conductivity
Electron flow
A property of element
Take place in solid &liquid
No chemical change occur
Electrolytic conductivity
Ions flow
A property of polar compounds
Take place in liquid & solution
Chemical change occur

17. In an electrolytic cell: Anode is a Positive electrode
Cathode is a negative electrode
REMEMBER
the story?

18. Anode Oxidation
Story of
An Ox Red Cat
&
Reduction Cathode

19. Positive Anode Negative Is Cathode Don’t get stressed in the exam:
Remember PANIC

20. Some key differences with an electrochemical cell set-up:
No salt bridge
An electrochemical cell will be required
Anode is POSITIVE electrode
Cathode is NEGATIVE electrode

21. WHAT HAPPENS IN ELECTROLYSIS
BATTERY
(Electron pump)
Electrons move back
to battery to complete
the circuit
Electron flow
Negatively charged
ion
Positively
charged
ion
Give up electrons to the
electrode
Electron leave
the electrode
Ions discharged as atom
Ions
discharged as atom
Anode(+)
Cathode(-)
Electrolyte

22. WHAT HAPPENS IN ELECTROLYSIS
BATTERY
(Electron pump)
Electrons move back
to battery to complete
the circuit
Electron flow + _ + _ _ +
Anode(+)
Cathode(-)
Electolyte

23. Think of electrolysis and electrolytic cells as the opposite of electrochemical cells:

24. Chemical → Electrical Electrical → chemical Yes No
Electrochemical Cells
Electrolytic
Cells
Energy conversion
Spontaneous chemical
reaction?
Value of E°
Examples
Chemical → Electrical
Electrical → chemical
Yes No
Positive
Negative
recharging batteries & electroplating
batteries

25. IN THE PROCESS OF ELECTROLYSIS
Conduction of Electricity
Supplying of energy
Carrying of electric current
Note:
Electrons do not actually pass through the liquid.

26. PROCESS OF ELECTROLYSIS
Movement of ions
Cations = Cathode
Anions = Anode
Discharge of ions
ALWAYS PRODUCE
AT CATHODE
METAL OR HYDROGEN

27. ELECTROLYSIS OF MOLTEN NaCl 2NaCl(s) → 2Na+ (l) + Cl-(l)
EXAMPLE
ELECTROLYSIS OF MOLTEN NaCl
2NaCl(s) → 2Na+ (l) + Cl-(l)

28. Sodium metal at the (-)Cathode
2Na+  +  2e- →   2Na
Chlorine gas at the (+)Anode
2Cl-  -  2e-   →  Cl2
The overall reaction is
2Na+Cl-(l)   →   2Na(s)  +   Cl2(g)

29. Electrolysis of Molten NaCl- +
ANODE
CATHODE
The metal goes to the cathode and the non metal goes to the anode. - +
Na+
Cl-
Cl-
Cl-
Na+
Na+
Na+
Cl-

30. Activity

31. Splitting a substance using electricity
Match up the words with their descriptions
Positive electrode
Electrolyte
The substance being broken down
Anode
Splitting a substance using electricity
Cathode
Negative electrode
Anion
Positive ion
Cation
Negative ion
Electrolysis

32. VIDEO OF ELECTROLYSIS

33. Factors affecting the SELECTIVE discharge of ions
SELECTIVE discharge of ions? FACTORS:- 1.Relative positions of the ion in the metal activity series. 2. The concentration of ions in the electrolyte 3. The nature of electrode

34. 1-RELATIVE POSITIONS OF THE ION IN THE METAL ACTIVITY SERIES.

35. 2. The concentration of ions in the electrolyte
FACTORS (Contd)
2. The concentration of ions in the electrolyte
Higher the concentration of ions in the electrolyte ……………..?
3. The nature of electrode
Inert electrodes : iron, carbon, platinium
Active electrodes : copper, nickel

36. PREDICTING WHAT WILL BE FORMED IN AN ELECTROLYSIS
Compound
Anode
Cathode
Sodium Bromide
Potassium Iodide
Calcium Fluoride
Magnesium Oxide
Lithium Chloride
Bromine
Sodium
Iodine
Potassium
Fluorine
Calcium
Oxygen
Magnesium
Chlorine
Lithium

37. PREPARATION OF ALKALI & CHLORINE GAS
ELECTROPLATING
EXTRACTION OF METALS
ANODIZING
ELCTROREFINING
PREPARATION OF ALKALI & CHLORINE GAS
Industrial
Application of electrolysis

38. Increasing reactivity
Extraction processes
The reactivity of a metal determines the method of extraction.
The Reactivity
Series
potassium
Increasing reactivity
sodium
Metals above carbon must be extracted using electrolysis.
calcium
magnesium
aluminium
(carbon)
zinc
Metals below carbon
can be extracted from the ore by reduction using carbon, coke, or charcoal.
iron
lead
copper
silver
Gold and silver often do not need to
be extracted. They occur native.
gold

39. 1- EXTRACTION OF METALS EXAMPLE = ALUMINIUM METAL)
Electrolysis of molten Alumina
The electrolyte a solution of alumina in cryolite melts at about 900 °C and electrolysis is done at about 950 °C.
Electrolysis separates the molten ionic compound into its elements.

40. Electrolysis of molten Alumina

41. REACTIONS Aluminium metal at the (-)cathode
4Al3+  +  12e-   → 4Al  (Reduction)
Oxygen gas at the (+)anode
6O2-    → 3O2  +  12e- (Oxidation)
The overall reaction
2Al2O3(l)  →      4Al(l)   +     3O2(g)

42. 2-PREPARATION OF ALKALI & CHLORINE GAS
The NaCl will split into Na+ and Cl - ions
Water splits into H + and OH - ions.
Qs?
What will happen during electrolysis?

43. 2-PREPARATION OF ALKALI & CHLORINE GAS

44. REACTIONS At the Cathode 2H+ + 2e- → H2 At the Anode 2Cl– → Cl2 + 2e-
The overall reaction
2NaCl + 2H2O → Cl2 + H2 + 2NaOH

45. NELSON CELL

46. 3- ELECTROPLATING PURPOSE?
Most commonly used metals for electroplating
Copper, Chromium, Silver, Tin

47. Gold plating cathode: Au+(aq) +e-→Au anode: Au→Au+(aq) +e-
external power source
external power source Au Au
Au+(aq)
Au+(aq)
cathode:
Au+(aq) +e-→Au
anode:
Au→Au+(aq) +e-

48. 4-ELECTRO REFINING OF METALS
is a process by which metals containing impurities are purified by electrolysis to give a pure metal.
EXAMPLE:-
ELECTRO REFFINING OF COPPER

49. ELECTRO REFINING OF COPPER
ELECTROLYTE
Aqueous copper sulphate solution
ELECTRODES
CATHODE : pure thin sheet of copper
ANODE : Impure block of copper
IONS PRESENT
CuSO Cu2+ + SO42-
H2O H+ + OH-
REACTION AT THE CATHODE
Cu2+ ions are discharged at the cathode as neutral copper atoms.
Cu e Cu
REACTION AT THE ANODE
Copper anode itself loses electrons to give Cu2+ ions in solution.
Cu Cu e

51. COPPER REFINING

52. Work sheet
1. While the experiment is running answer these questions in your note book.
Why must the blister copper be purified before use?
At the anode copper atoms are going to dissolve. What will they become?
Write an equation for this. Is this reaction reduction or oxidation?
At the cathode new copper atoms are going to be formed.
d) What do you think will happen to the masses of each electrode?

53. Make a summary of the work covered

54. Concept Map

55. REFERENCES
BOOKS:
1- Chemistry ‘A course for O’level’ by Christopher N. Prescott
2- New edition chemistry by Richard Harwood
3- GCSE chemistry by M.J.Denial
4- GCSE chemistry for class X by R D Madan & B.S.Bisht
5- Chemistry for class IX, STBB
WEBSITES:

56. 30/09/99
The End
Starring Ms Farzana

57. THANK YOU