PRESENTER MS FARZANA MEHBOOB Head of the Science department

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