CH302 Worksheet 11b. Balancing Redox reactions and assigning cell convention. Use the table of standard reduction potentials below as required. Half reaction Eo Li+ + e- = Li -3.04 Na+ + e- = Na -2.71 Mg+2 + 2e- = Mg -2.38 Al+3 + 3e- = Al -1.66 2H2O + 2e-= H2(g) + 2OH - -0.83 Zn+2 + 2e-= Zn -0.76 Cr+3 + 3e-= Cr -0.74 Fe+2 + 2e-= Fe -0.41 Cd+2 + 2e-= Cd -0.40 Ni+2 + 2e-= Ni -0.23 Sn+2 + 2e-= Sn -0.14 Pb+2 + 2e-= Pb -0.13 Fe+3 + 3e-= Fe -0.04 2H+ + e-= H2 0.00 Half reaction Eo Sn+4 + 2e-= Sn+2 +0.15 Cu+2 + e- = Cu+ +0.16 Cu+2 + 2e-= Cu +0.34 I2 + 2e-= 2I- +0.54 Fe+3 + e- = Fe+2 +0.77 Ag+ + e- = Ag +0.80 Hg+2 + 2e- = Hg +0.85 NO3- + 4H+ + 3e-= NO + 2H2O +0.96 Br2 + 2e- = 2Br- +1.07 O2 + 4H+ + 4e-= 2H2O +1.23 Cr2O7-2 + 14H++ 6e- = 2Cr+3 + 7H2O +1.33 Cl2 + 2e- = 2Cl- +1.36 MnO4-2 + 8H+ + 5e-= Mn+2 + 4H2O +1.49 F2 + 2e-= 2F- +2.87 15 reactions to use in answering the questions below. Dr. Laude’s demos (balance by inspection) 1. H2 + O2 Æ H2O 2. Na + H2O Æ Na+ + OH- + H2 3. C6H12O6 + O2 Æ CO2 + H2O Simple redox reactions (use change of oxidation method) 4. Cu + Zn++ Æ Zn + Cu++ 5. Al + Fe+3 Æ Al+3 + Fe+2 6. Pb + Cr+3 Æ Pb+2 + Cr 7. Li + F2 Æ Li+ + F- Acid (use change of oxidation method in acid) 8. Mn+2 + I2Æ MnO4- + I- 9. BrO3- + N2H4 Æ Br- + N2 10. Fe+3 + H2O Æ O2 + Fe+2 11. P4 + NO3- Æ H2PO4- + NO 12. Cr2O7-2 + Sn+2 Æ Cr+3 + Sn+4 Base (use change of oxidation method in base) 13. CN- + MnO4- Æ MnO2 + CNO- 14. Fe(OH)2 + O2 Æ Fe(OH)3 15. C2H5OH + MnO4- Æ C2H3O2- + MnO2 Part I. Balance all of the electrochemical (redox) reactions above. Refer to Worksheet 11a for assistance in how to perform the “change of oxidation method” approach. For those who are more comfortable with the “half reaction method”, feel free to use that. It yields the same result—it just wastes a lot of time. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Part II. Standard Cell Potential. Assuming standard conditions, calculate the standard cell potential for reactions: 2, 4, 5, 6, 7, 8, 10 and 12 for the reaction as written, using the equation Eocell = Eocathode -Eoanode Reaction: Cell Potential 2 4 5 6 7 8 10 12 Part III. Cell convention. For reactions 2, 4, 5, 6, 7, 8, 10 and 12 as written above, find the following for the electrochemical cell assuming the reaction is as written: reaction voltaic or electrolytic Half reaction at + electrode Half reaction at - electrode 2 4 5 6 7 8 10 12 Part IV. Cell shorthand notation. No one likes to draw all those beakers and wires in an electrochemical cell (except people who like to draw), so electrochemists have developed shorthand electrochemical notation. Use it to draw the electrochemical cells of reactions 2, 4, 5, 6, 7, 8, 10 and 12. Reaction: Cell Shorthand 2 4 5 6 7 8 10
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