PRESENTER
MS FARZANA MEHBOOB
Head of the Science department
D.A.Neelum high school
INSTRUCTIONAL LESSON
ELECTROLYSIS
TOPIC:
Electrolysis &
its
Application
Division of lesson
• Qualitative Aspect of Electrolysis
• Quantitative Aspect of Electrolysis
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
BLOOM BASED OBJECTIVES
ANALYSING
Use a Venn diagram to show how electrolytic cell and electrochemical cell are similar and different.Conduct an experiment to check whether sodium chloride can act as an electrolyte in solid state or can not. Give reason.
(Highorder thinking)
BLOOM BASED OBJECTIVES(Highorder thinking)
EVALUATING
Form a panel to discuss the influence of electrolysis on our lives.
State one advantage of Down process from a pollution point of view and also one commercial advantage.
BLOOM BASED OBJECTIVES(Highorder thinking)
CREATING
Suggest how could the experiment be changed to avoid the formation of poisonous fumes of chlorine gas in the given experiment.
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
Humphry Davy1778-1829.Prepared metallic K, Na, Sr, Ca, B, Ba, Mg, Li by electrolysis.
Electrolysis
Electrolysis
Electro
electricity
and lysisBreak
apart
WHAT IS ELECTROLYSIS
DEFINITION
through
resulting
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.
GENERAL TERMS USED IN ELECTROLYSIS
Electrolytic cell It has three component parts:
1.An electrolyte 2.Two
electrodes (a cathode and an anode).
3.A battery
• 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
TYPES OF ELECTROLYTE
ELECTRICAL CONDUCTIVITY
Metallic conductivity
Electron flow
Electrolytic conductivity
• In an electrolytic cell:Anode is a Positive electrode Cathode is a negative electrode
Electrode
REMEMBER
the story?
An Ox
Red Cat
Anode OxidationStory of
&
Reduction Cathode
•Positive•Anode•Negative
•Is•Cathode
Don’t get stressed in the exam:
Remember PANIC
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
BATTERY(Electron
pump)
Electron flowElectrons move back to battery to complete the circuit
Negatively charged ion
Give up electrons to theelectrode
Ions discharged as atom
ElectrolyteAnode(+)
Cathode(-)
Positively charged ion
Electron leave the electrode
Ionsdischarged as atom
WHAT HAPPENS IN ELECTROLYSIS
BATTERY(Electron
pump)
Electron flowElectrons move back to battery to complete the circuit
ElectolyteAnode(+)
Cathode(-)
WHAT HAPPENS IN ELECTROLYSIS
+
+_
_
_+
Think of electrolysis and electrolytic cells as the
opposite of electrochemical cells:
Electrochemical Cells
Electrolytic Cells
Energy conversion
Spontaneous chemical reaction?
Value of E°
Examples
Electrical → chemical
No
Chemical → Electrical
Yes
Positive
batteries recharging batteries & electroplating
Negative
IN THE PROCESS OF ELECTROLYSIS
Conduction of Electricity
Supplying of energy
Carrying of electric current
• Note: Electrons do not actually
pass through the liquid.
• Movement of ions– Cations = Cathode– Anions = Anode
• Discharge of ions
PROCESS OF ELECTROLYSIS
AT CATHODEALWAYS PRODUCEMETAL OR HYDROGEN
EXAMPLE
• ELECTROLYSIS OF MOLTEN NaCl
2NaCl(s) → 2Na+ (l)
+
Cl-(l)
Sodium metal at the (-)Cathode
2Na+ + 2e- → 2Na Chlorine gas at the (+)Anode
2Cl- - 2e- → Cl2
• The overall reaction is2Na+Cl-
(l) → 2Na(s) + Cl2(g)
Electrolysis of Molten NaCl
+ -
-+
CATHODEANODE
Na+
Cl-
Na+
Cl-
Na+
Cl-Na+
Cl-
The metal goes to the cathode and
the non metal goes to the anode.
Activity
Match up the words with their descriptions
ElectrolyteThe substance being broken down
Splitting a substance using electricity
Electrolysis
Positive electrode
Negative electrode
Anode
Cathode
Anion
Negative ion
Positive ion Cation
VIDEO OF ELECTROLYSIS
Factors affecting the SELECTIVE
discharge of ionsSELECTIVE 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
1-RELATIVE POSITIONS OF THE ION IN THE METAL ACTIVITY SERIES.
FACTORS (Contd)
2. The concentration of ions in the electrolyteHigher the concentration of ions in the electrolyte ……………..?
3. The nature of electrode
Inert electrodes : iron, carbon, platinium
Active electrodes : copper, nickel
Compound Anode Cathode
Sodium Bromide
Potassium Iodide
Calcium Fluoride
Magnesium Oxide
Lithium Chloride
PREDICTING WHAT WILL BE FORMED IN AN ELECTROLYSIS
Bromine Sodium
Iodine Potassium
Fluorine Calcium
Oxygen Magnesium
Chlorine Lithium
ELECTROPLATING
EXTRACTION OF
METALS
ANODIZING
ELCTROREFINING
PREPARATION OF ALKALI & CHLORINE
GASIndustrialApplication of electrolysis
Extraction processes
The ReactivitySeries
potassiumsodiumcalciummagnesium
aluminium
zinciron
copper
gold
(carbon)
Incr
easi
ng
rea
ctiv
ity
Metals above carbon must be extracted using electrolysis.
Metals below carboncan be extracted from the ore by reduction using carbon, coke, or charcoal.
Gold and silver often do not need to be extracted. They occur native.
The reactivity of a metal determines the method of extraction.
lead
silver
1- EXTRACTION OF METALS EXAMPLE = ALUMINIUM METAL)
Electrolysis of molten Alumina
• The electrolyte a solution of alumina in cryolite melts at about 900 °Cand electrolysis is done at about 950 °C.
• Electrolysis separates the molten ionic compound into its elements.
Electrolysis of molten Alumina
REACTIONS
• Aluminium metal at the (-)cathode4Al3+ + 12e- → 4Al (Reduction)
• Oxygen gas at the (+)anode 6O2- → 3O2 + 12e- (Oxidation)
The overall reaction 2Al2O3(l) → 4Al(l) + 3O2(g)
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?
2-PREPARATION OF ALKALI & CHLORINE GAS
REACTIONS
• At the Cathode2H+ + 2e- → H2
• At the Anode2Cl– → Cl2 + 2e-
The overall reaction
• 2NaCl + 2H2O → Cl2 + H2 + 2NaOH
NELSON CELL
3- ELECTROPLATING • PURPOSE?
• Most commonly used metals for electroplating
• Copper, Chromium, Silver, Tin
47
cathode:Au+(aq) +e-→Au
anode:Au→Au+(aq) +e-
external power source
Au
Au+(aq) Au+(aq)
Au
external power source
Gold plating
–is a process by which metals containing impurities are purified by electrolysis to give a pure metal.
• EXAMPLE:- ELECTRO REFFINING OF
COPPER
4-ELECTRO REFINING OF METALS
ELECTROLYTE Aqueous copper sulphate solution
ELECTRODES CATHODE : pure thin sheet of copperANODE : Impure block of copper
IONS PRESENT CuSO4 Cu2+ + SO42-
H2O H+ + OH-
REACTION AT THE CATHODE Cu2+ ions are discharged at the cathode as neutral copper atoms.
Cu2+ + 2e Cu
REACTION AT THE ANODE Copper anode itself loses electrons to give Cu2+ ions in solution.
Cu Cu2+ + 2e
ELECTRO REFINING OF COPPER
COPPER REFINING
1. While the experiment is running answer these questions in your note book.
a) Why must the blister copper be purified before use?
b) At the anode copper atoms are going to dissolve. What will they become?
c) 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?
SUMMARYMake a summary
of the work covered
Concept Map
REFERENCES• BOOKS:1- Chemistry ‘A course for O’level’ by Christopher N. Prescott
2- New edition chemistry by Richard Harwood3- GCSE chemistry by M.J.Denial4- GCSE chemistry for class X by R D Madan & B.S.Bisht5- Chemistry for class IX, STBB• WEBSITES:www.britannica.comwww.thinkquest.comwww.yteach.comwww.wikipedia.org
www.youtube.com
The EndStarringMs Farzana
THANK YOU