Electrochemical Cells

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A set of slides created to teach Electrochemical Cells to learners at Bishops Diocesan College in Cape Town.

A set of slides created to teach Electrochemical Cells to learners at Bishops Diocesan College in Cape Town.

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  • 1. ELECTROCHEMICAL CELLS K Warne
  • 2. Electrochemical Cell.  REDUCING AGENT Two metals can react indirectly. _e- anode > V cathode Salt bridge + Attract elelctons weakly Zn2++ 2e- --> Zn Zn Cu _ KNO3(aq) _ _ _ ZnSO4 CuSO4 _ _ _ REDUCING AGENT OXIDISING AGENT oxidation Zn  Zn2+ + 2e- reduction Cu2+ + 2e-  Cu Zn + Cu2+  Zn2+ + Cu Top right reacts with bottom left. Cu2+ + 2e- --> Cu Attract elelctons strongly OXIDISING AGENT
  • 3. WORKED EXAMPLES 1. The redox couples Mn2+(aq) Mn(s) and U3+(aq) U(s) have Eθ values of –1.18 and –1.79 respectively. Determine Eθcell when they are combined and write an equation for the reaction that takes place. Eθcell = EθO.A. - EθR.A. = -1.18 – (-1.79) = +0.61v 3Mn2+(aq) + 2U(s)  3Mn(s) + 2U3+(aq) 2. The redox couples Co2+(aq) Co(s) and Ni2+(aq) Ni(s) have Eθ values of –0.28v and –0.23v respectively. Write an equation for the spontaneous reaction and use the Eθ values to justify your answer. Co(s) + Ni2+(aq)  Co2+(aq) + Ni(s) Eθ = Eθ O.A - Eθ R.A = -0.23 – (-0.28) = +0.05v Ni2+(aq) + Co(s) Co2+(aq) + Ni(s)
  • 4. Electrolysis – Electrolytic Cell - + Copper chloride CuCl2 Cu2+ (aq)+ 2e-  Cu(s) REDUCTION CATHODE  ClCu2+ 2Cl- (aq)  Cl2(g) + 2eOXIDATION Anode Electrolytic cell: Converts electrical energy to chemical energy. SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> ScienceCafe
  • 5. STANDARD HYDROGEN ELECTRODE        SAMPLE ONLY SAMPLE ONLY ……….. electrode H2 gas pressure of ………. (………. kPa) Solution of …..M H+ ions (HCl) …………K Eθ = ……………v S.H.E. is ………. to set up. ……………….. standard electrodes used. SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
  • 6. DETERMINATION OF CELL POTENTIALS Unknown electrode Standard electrode High resistance voltmeter N+(s) Salt bridge N+(aq)     If a cell potential of 1.45v is obtained with metal N. Then the electrode potential of N+ /N is .................................. .................................. .................................. .................................. Eθ values are determined using a ……………………………… electrode. The S.H.E is always the …………………. electrode. Standard Conditions : …………………………………………………. A secondary standard electrode the ………………. electrode can be used. Eθcell= ………………………………………… SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY Eθcell= ………………. – ………. For FULL presentation click HERE >> www.warnescience.net
  • 7. Electrolysis in aqueous solutions Na+ + e- Na The most positive system 2+ + 2eMg present will Mg react at the 2H2O + 2e cathode H2 + 2OH - -2.71 -2.37 - -0.83 Cu2+ + 2e- Cu H2 + 2e- 2H+ SO42- + 4H+ + 2e- SO2 +0.17 H2O + O2 + 2e- 4OH- +0.40 Cl2 + 2eSAMPLE ONLY 2Cl- +0.34 +1.36 SAMPLE ONLY ? Cathode: Reduction Cu2+ + 2eCu Which ions will react at which electrodes? + Anode: Oxidation SAMPLE Cl2 + 2e- ONLY 2Cl For FULL presentation click HERE >> www.warnescience.net
  • 8. Electrochemical Cells Voltaic (Galvanic) vs Electrolytic _ > V Salt bridge e-Zn + Cu KNO3(aq) _ _ _ _ ZnSO4 _ _ CuSO4 _ Electrical Energy e-  Electrical Energy Copper chloride - Chemical Energy CuCl2 +  ClREDUCING AGENT oxidation Zn  Zn2+ + 2eAnode (-) OXIDISING AGENT Cu2+ reduction Cu2+ + 2e-  Cu Cathode Zn + Cu2+  Zn2+ + Cu (+ ) Chemical Energy  Electrical Energy SAMPLE ONLY Chemical Energy Cu2+ (aq)+ 2e-  Cu(s) 2Cl- (aq)  Cl2(g) + 2eREDUCTION OXIDATION CATHODE Anode (-) (+) Electrical Energy  Chemical Energy SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
  • 9. Electrolysis of aqueous solutions (MX) - + M+ X- (Non-Metal (Metal ion) ion) (H2O) If the metal is more positive than hydrogen, its ions will be reduced. M+ + e  M SAMPLE ONLY If halide ions (X-) are present (more positive than OH- ) ions then the halide ions (X-) are oxidised. X-  X2 + 2eSAMPLE ONLY SAMPLE ONLY SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net
  • 10. Electrolysis - Lead Bromide electrons PbBr2 (Heat) Pb2+ + BrPbBr2 - Pb2+ (l) + 2e-  Pb(l)  SAMPLE ONLY + 2Br - (l)  Br2(g) + 2e- SAMPLE ONLY SAMPLE ONLY Pb2+ (l) + 2Br -(l)  >> www.warnescience.net Pb(l) + Br2(g) For FULL presentation click HERE
  • 11. Electrolysis – Sodium chloride 2H2O + 2e-  H2 + 2OH- 2Cl-  Cl2 + 2e- SAMPLE ONLY SAMPLE ONLY 2HSAMPLE ONLY+ (2Na+)  Cl2 + H2 + 2OH- + (2Na+) O + 2Cl2 For FULL presentation click HERE >> www.warnescience.net
  • 12. WarneScience Hi… This is a SAMPLE presentation only. My FULL presentations, which contain a lot more slides and other resources, are freely available on my resource sharing website: www.warnescience.net (paste into your browser if link above does not work) Have a look and enjoy! SAMPLE ONLY Keith Warne SAMPLE ONLY SAMPLE ONLY For FULL presentation click HERE >> www.warnescience.net