In voltaic cells, the redox reaction is spontaneous, so it doesn’t require an outside energy source.
Electro chemical cells
PRESENTATION OF CHEMISTRY
PRESENTED TOMA’AM TAHIRA TARIQ PRESENTED BY HINA JABEEN ROLL NO: 120
TEACHING MATERIALS White board Duster Marker Books
GENERAL OBJECTIVES Enable the student to acquire comprehension of chemistry. To compare learnt knowledge with surrounding. To develop interest among student towards chemistry. Enable the student to apply the leant knowledge.
SPEACIFIC KNOWLEDGEAt the end of the topic student will be able to Sketch a Denial cell, label cathode, anode and direction of the flow of electron. Distinguish between electrolytic and voltaic cell. Identify half cell in which oxidation occur and half cell in which reduction occur in voltaic cell.
Previous knowledge Define electro chemical cell? What are the types of electro chemical cell, name them? Define electrolytic cell and voltaic cell?
INTRODUCTION ELECTRO CHEMICAL CELL: An arrangement which consist of electrodes dipped into an electrolyte in which chemical reaction uses/generates electric current . ELECROLYTIC CELL: The electro chemical cell in which a reaction occur with the help of electric current. VOLTAIC/GALVANIC CELL: The electro chemical cell in which a reaction generates electric current.
ELECTRO-CHEMICAL REACTIONWe discuss electrolysis of :A) fused saltB) Aqueous solution of salt
Electrolysis of aq. sol. of Salt Not so simple Reason Undergoes REDOX reaction of H2O•Along with redox reaction of dissolved salt•Product -------not precisely predicted e.g. KNO3
Electrolysis of aq. Sol of KNO3 It dissociate as: KNO3 K+ + NO3-H2O + H2O H3O+ + OH-
Aqueous KNO3 - battery + power source e- e- KNO3 (aq) What could be reduced at the cathode? K+ NO3- (-) (+) cathode H2O anode different - half-cell
Reaction at cathode from+K KNO3 Not discharge At cathodeReason Small concentration H3O +& OH- Formed By Dissociation of H2O
H3O + takes e- from cathode Formed Hº Hº Hº Combine H2 At Cathode
Reaction at anodeNO3 - Tendency AnodeOH- To move - Oxidation of OH - Easier than NO3 OH - discharge O2 + H2O
RESULT - K+ & NO3 remain in solution Water is electrolyzed and converted into H2 and O2 H2O is electrolyzed in presence of KNO3
Voltaic Cells Invented by Alessandro Volta in 1800 Voltaic cells: electrochemical cells used to convert chemical energy into electrical energy Examples flashlights or battery- powered calculators Made of half cells One part of the voltaic cell where oxidation or reduction is occurring
VOLTAIC CELL/GALVANIC CELL:To understand the working of voltaic cell, take example of Daniel cell
GALVANIC CELL/ VOLTAIC CEL TWO HALF CELLSLEFT HALF CELL RIGHT HALF CELL CONNECTED THROUGH SLT BRIDGE
LEFT HALF CELL CONTAINS Zn METAL STRIP DIPPED INGiving equilibrium 1M ZnSO4 ANODE
RIGHT HALF CELL CONTAINS COPPER METAL STRIP DIPPED INGiving equilibrium 1M Cu SO4 CATHODE
CellConstruction Cu Zn 1.0 M CuSO4 1.0 M ZnSO4
leave Zn electrode e - Cu electrode Zn CuGIVING NET GIVING NET+ive CHARGE -ive CHARGE Electron flow from External circuit Zn electrode Cu electrode
What about half-cell What about the sign of reactions? the electrodes? + - Why? cathode half-cell anode half-cellCu+2 + 2e- Cu Zn Zn+2 + 2e- Cu Zn plates out What electrode or happened erodes deposits Cu at each Zn or dissolves on electrode? electrode 1.0 M CuSO4 1.0 M ZnSO4
flow1.1V current Zn electrode from to through External circuit Cu electrode Reduction Cu electrode having Oxidation Zn electrode concentration 1 M solution each Temperature = 25˚c
Now replace the light bulb with a volt meter. + 1.1 volts - cathode half-cell anode half-cellCu+2 + 2e- Cu Zn Zn+2 + 2e- Cu Zn 1.0 M CuSO4 1.0 M ZnSO4
SALT BRIDGEStrong Electrolyte KCL, KNO3, K2SO4 Saturated Solution of Porous Ends at both sides Sealed Glass / Wool / Cotton Plug
Comparison of Electrochemical Cells Galvanic Electrolytic Produces electrical current Need power source Non spontaneous Spontaneous redox reaction redox reaction Electric condition Electrolysis take place take place
FILL IN THE BLANKS ____________of aq. Sol. of salt is not so simple Electrolysis of aq. Sol. of _____is not so simple KNO3 < >______ +NO ¯ 3 _______< > K+ +NO ¯ 3 H O +e< 2 > Hº + ______
Two _______atom combine to form hydrogen gas Hydrogen gas is formed by the combination of two ________ atoms. OH¯ OHº + e 4OH- O2 +_________ In electrolysis of water, H2O is converted into_____ and _____ _______ is used as electrolyte in electrolysis of H2O _______ cell is an example of voltaic cell
1. Voltaic/galvanic cell consist of _____ half cell2. Two half cell are connected through ___________3. Right half cell contain _____ metal strip4. Left half cell contain _____ metal strip5. Cu metal strip is dipped into 1M sol. Of ______6. Zn metal strip is dipped into 1M sol. Of ______7. Sum of two half cell reaction is called ________ reaction
1. Salt bridge is _____ shape2. Salt bridge is made up of ______ tube3. Tube of salt bridge is ______ at both end4. End of salt bridge Is made up of _____ material5. _______ material hold the solution in U shaped
Identify the following Anode Cathode + 1.1 volts - Salt bridge Cu Zn