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 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) 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) 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 Davy 1778-1829. Prepared metallic K, Na, Sr, Ca, B, Ba, Mg, Li by electrolysis. Electrolysis
Electro electricity and lysis Break apart through Latin word 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
ELECTRICAL CONDUCTIVITY 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 Is of two types
In an electrolytic cell: Anode is a Positive electrode Cathode is a negative electrode Electrode REMEMBER the story?
An Ox Red Cat Anode Oxidation Story 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 flow Electrons move back to battery to complete the circuit Negatively charged ion Give up electrons to the electrode Ions discharged as atom Electrolyte Anode(+) Cathode(-) Positively charged ion Electron leave the electrode Ions discharge d as atom
BATTERY (Electron pump) Electron flow Electrons move back to battery to complete the circuit Electolyte Anode(+) Cathode(-) + + _ _ _ +
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 CATHODE ALWAYS PRODUCE METAL 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 - → Cl 2 The overall reaction is 2Na + Cl - (l) → 2Na (s) + Cl 2(g)
Electrolysis of Molten NaCl + - - + CATHODE ANODE Na + Cl - Na + Cl - Na + Cl - Na + Cl - The metal goes to the cathode and the non metal goes to the anode.
Match up the words with their descriptions Electrolyte The substance being broken down Splitting a substance using electricity Electrolysis Positive electrode Negative electrode Anode Cathode Anion Negative ion Positive ion Cation
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.
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
CompoundAnodeCathode Sodium Bromide Potassium Iodide Calcium Fluoride Magnesium Oxide Lithium Chloride PREDICTING WHAT WILL BE FORMED IN AN ELECTROLYSIS Bromine Sodium IodinePotassium FluorineCalcium OxygenMagnesium Chlorine Lithium
ELECTROPLATING EXTRACTION OF METALS ANODIZINGELCTROREFINING PREPARATION OF ALKALI & CHLORINE GAS Industrial Application of electrolysis
Extraction processes The Reactivity Series potassiu m sodium calcium magnesium aluminium zinc iron copper gold (carbon) Increasing reactivity Metals above carbon must be extracted using electrolysis. Metals below carbon can 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 °C and electrolysis is done at about 950 °C. Electrolysis separates the molten ionic compound into its elements.
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 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
ELECTROLYTEAqueous copper sulphate solution ELECTRODESCATHODE : pure thin sheet of copper ANODE : Impure block of copper IONS PRESENTCuSO 4 Cu 2+ + SO 4 2- H 2 O H + + OH - REACTION AT THE CATHODECu 2+ ions are discharged at the cathode as neutral copper atoms. Cu 2+ + 2e Cu REACTION AT THE ANODECopper anode itself loses electrons to give Cu 2+ ions in solution. Cu Cu 2+ + 2e ELECTRO REFINING OF COPPER
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?
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