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 (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.

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.

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..

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

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

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.

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

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

Anode Oxidation Story of An Ox Red Cat & 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

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

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

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

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

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

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

ELECTROLYSIS OF MOLTEN NaCl 2NaCl(s) → 2Na+ (l) + Cl-(l) 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 is 2Na+Cl-(l)   →   2Na(s)  +   Cl2(g)

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-

Activity

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

VIDEO OF ELECTROLYSIS

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

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

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

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

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

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

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.

Electrolysis of molten Alumina

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)

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 Cathode 2H+ + 2e- → H2 At the Anode 2Cl– → 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

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-

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

ELECTRO REFINING OF COPPER ELECTROLYTE Aqueous copper sulphate solution ELECTRODES CATHODE : pure thin sheet of copper ANODE : 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

COPPER REFINING

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?

Make 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 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: www.britannica.com www.thinkquest.com www.yteach.com www.wikipedia.org www.youtube.com

30/09/99 The End Starring Ms Farzana

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