Electochemical

Electrochemical Cells Tutorial sheet 1. Calculate the single electrode potential for copper metal in contact with 0.10M Cu+2 solution. E˚ for copper electrode is 0.34V. 2. Calculate EMF of the cell involving the reaction : Mg(s)+ 2Ag+(aq) → Mg+2(aq) + 2Ag(s) Given; [Mg+2] = 0.130M and [Ag+] = 1.0x10-4M & E˚Ag+/Ag = 0.80V and E˚Mg+2/Mg = -2.37V. 3. Calculate the EMF of the cell: Zn│Zn+2(1M)║ Ag+(1M)│Ag ; Given; E˚Zn/Zn+2 = 0.762V and E˚Ag+/Ag = 0.800V. 4. Predict whether the following reaction is feasible or not: 2Ag(s)+Zn+2(aq)→2Ag+(aq)+ Zn(s) is feasible or not. Given; E˚Ag+/Ag = 0.80V and E˚Zn+2/Zn = - 0.763V.
5. Determine the feasibility of the reaction, 2Al(s) + 3Sn+4(aq) → 2Al+3 + 3Sn+2(aq); Given; E˚Al+3/Al = -1.66V and E˚Sn+4/Sn+2 =+0.15V.
6. What is the potential of Zn electrode in 0.01M ZnSO4 solution at 25˚C if E˚ is 0.763V.
7. Calculate the EMF of the cell: Zn│Zn+2(0.001M)║ Ag+(0.1M)│Ag; Given; E˚Ag+/Ag = +0.80V and E˚Zn/Zn+2 = -0.76V.
8. The EMF of the following cell at 25˚C is 0.4450V: Pt ; H2(1atm)│H+(test sol) │KCl salt sol │ Hg2Cl2 │Hg. Calculate the pH of the unknown solution. Ecalomel = 0.2415V.
9. Find the pH of a solution placed in a hydroquinone half-cell which was coupled with standard calomel electrode. The EMF of the combined cell was determined to be 0.123V at 25˚C. Ecalomel = 0.2415V and E˚Q = 0.6996V. 10 . A Zn rod is placed in 0.1M solution of ZnSO4 at 25˚C. Assuming that the salt is dissociated to95% at this dilution, calculate the potential of the electrode at this temperature. Given; E˚(Zn+2/Zn) = -0.76V.
11. Write the cell reaction for the cell: Zn, Zn+2(1M) │Fe+2(1M), Fe+3(1M); Pt.
12. Calculate the potential of the cell and write down the cell reaction: Co│Co+2(0.01M)║ Pd+2(0.5M)│Pd Given; E˚Co+2/Co = -0.28V and E˚Pd+2/Pd = 0.99V.
13. Calculate the equilibrium constant for the reaction between AgNO3 & metallic Zn. Given; E˚Zn+2/Zn = -0.76V & E˚Ag+/Ag = +0.80V. 14. The standard EMF of Daniel cell, Zn(s) + Cu+2(aq) Zn+2(aq) + Cu(s) is 1.10V. Calculate equilibrium constant of the cell reaction at 25˚C.
15. Set up the electrochemical cell for the reaction 2Fe+3(aq) + Sn+2(aq) 2Fe+2(aq) + Sn+4(aq) and calculate equilibrium constant for the reaction. Given; E˚Fe+3/Fe+2 = +0.77 and E˚Sn+4/Sn+2 = +0.15.
16. Is the following reaction feasible? Zn + H2SO4 ZnSO4 + H2(g); Given; E˚H+/H2 = 0 and E˚Zn+2/Zn = -0.76V.
17. Calculate the equilibrium constant of the reaction, 2Cu+(aq) → Cu+2(aq) + Cu Given; E˚Cu+/Cu = +0.52V and E˚Cu+2/Cu = +0.34V. 18. While determining the pH of a solution, the quinhydrone electrode, H+, Q, QH2 was used in combination with a saturated calomel electrode, Hg, Hg2Cl2(s); KCl(sat. sol) ║ H+(unknown); Q, QH2, Pt. The EMF of the cell was found to be 0.2640V at 25˚C. Calculate the pH of the solution at this temperature. Given; Ecalomel = +0.2422V at 25˚C and E˚(H+, Q, QH2) = +0.6996V.
19. Calculate the equilibrium constant at 25˚C for the reaction, Zn(s) + Cu+2(1M) Cu(s) + Zn+2(1M). E˚ for this cell is 1.10V.
20. A Zn electrode is placed in a 0.1M Zn2+ solution at 25˚C. Assuming that the salt is dissociated to the extent of 20% at this dilution, calculate the potential of electrode at this concentration. (E˚Zn+2/Zn = -0.76V). 21. Consider the cell,Zn│Zn+2(aq)(1.0M)║Cu+2(aq)(1.0M)│Cu. The standard reduction potentials are +0.35V for Cu+2(aq) + 2e- →Cu & -0.763V for Zn+2(aq)+2e-→Zn.(i)Write down the cell reaction.(ii)Calculate the EMF of the cell.(iii)Is the reaction spontaneous? 22. Consider the following cell, Cd │ Cd+2(1M) ║ H+(aq)(1M) │ H2(g) Pt. Write down the overall reaction indicating the anodic and cathodic half reactions. 23. Consider the reaction, 2Ag+ + Cd 2Ag + Cd+2 . Standard reduction potentials of Ag+/Ag and Cd+2/Cd couples are 0.80 and -0.40V, respectively. (i) What is the E˚ of this reaction? (ii) Which is negative electrode of the cell? 24. The following reaction takes place in a cell, Zn(s) + Co+2 Co(s) + Zn+2 Write down the electrode reactions and calculate the standard EMF of cell. Given; E˚Zn/Zn+2 = 0.76V and E˚Co/Co+2 = 0.28V. 25. What is the standard potential of a cell that uses the Zn+2/Zn and Ag+/Ag couples? Which couple is negative? Write the equation for the cell reaction occurring at unit relative concentration. The standard electrode potentials for Zn+2/Zn and Ag+/Ag are -0.763V and +0.779V, respectively. 26. The standard reduction potentials of Cu+2/Cu and Ag+/Ag electrodes are 0.337 and 0.799V, respectively. Construct a galvanic cell using these electrodes so that its standard EMF is positive. For what concentration of Ag+ will the EMF of the cell at 25˚C be zero if the concentration of Cu+2 is 0.01M? 27. EMF of a cell was found to be 0.1595V at 25˚C. Calculate the pH of acid solution. EMF of standard calomel and quinhydrone electrodes are +0.2440 and +0.6990V, respectively. 28. Write the cell reaction for Zn │ Zn+2(0.1N) ║ Ag+(0.01N) │ Ag. 29. Calculate the potential of an electrode consisting of Zn metal in ZnSO4 solution in which [Zn+2] = 0.01M for the reaction, Zn+2(aq) + 2e- Zn(s), E˚ = -0.76V. 30. Calculate the standard EMF of Ni+2/Ni electrode if the cell potential of the cell Ni│Ni+2(0.01M)║Cu+2(0.1M)│Cu is 0.59V. Given; E˚Cu+2/Cu = 0.34V. 31. Calculate the standard EMF of the cell, Cr(s)│Cr+3(aq)║Ag+(aq)│Ag(s); if E˚Cr/Cr+3 = +0.744V and E˚Ag/Ag+ = -0.80V. 32. Calculate the electrode potential of an M/M+3 electrode when [M+3] = 0.1M and E˚M+3/M = 0.77V. 33. Calculate the EMF of the cell, Zn(s)│ZnSO4(0.1M)║CuSO4(0.1M)│Cu(s), if E˚Zn+2/Zn = -0.763V and E˚Cu+2/Cu = +0.34V. 34. Calculate the reduction potential of Cu+2/Cu electrode at 25˚C, if the standard reduction potential of Cu+2/Cu is 0.34V and concentration of Cu+2 in solution is (i) 2M (ii) 0.2M. 35. Calculate the liquid junction potential at 25˚C between two solutions of HCl having mean ionic activities of 0.01 and 0.001, respectively. The transference number of H+ ion in HCl is 0.83. 36. Calculate liquid junction potential associated with the following cell, Ag(s),AgCl(s),HCl (m1=1.0,γ1= 0.809):HCl(m2=0.05,γ2=0.830),AgCl(s),Ag(s), if transference number of H+ is 0.83. 37. For the redox couples, Zn+2(aq)/Zn(s) and Cu+2(aq)/Cu(s), the reduction potentials are -0.76V and +0.34V, respectively. If the couples are combined, then: (i) Zn+2 is reduced and Cu+2 is oxidized (ii) Zn+2 is oxidized and Cu+2 is reduced (iii) None (iv) Any. 38 . EMF of standard cell, Zn│Zn+2║Ag+│Ag is 1.562V. If standard electrode potential of Zn is 0.762V, standard potential of Ag is: (i) 2.32V (ii) 0.80V (iii) -0.80V (iv) -2.32V. 39 . The standard reduction potentials, E˚ for half cell reactions are: Zn+2 + 2e- → Zn ; E˚ = +0.76V and Fe+2 +2e- → Fe ; E˚ = +0.41V The EMF of the cell reaction, Fe+2(aq) + Zn(s) Zn+2(aq) + Fe(s) is: (i) -0.35V (ii) +0.35V (iii) +1.17V (iv) -1.17V. 40. The EMF of the cell, Zn(s)│ZnSO4(1.0M)║CdSO4(0.01M)│Cd(s) is 0.33V. The reaction is: (i) spontaneous (ii) non-spontaneous (iii) reduction (iv) oxidation. 41. Which of the following is the best reducing agent? (i) Al (ii) Mg (iii) Cu (iv) I2 ; Given; E˚Al+3/Al = -1.67V; E˚Mg+2/Mg = -2.34V; E˚Cu+2/Cu = +0.34V; E˚I2/2I- = +0.53V. 42. The standard oxidation potential of Zn & Ag in water at 298K are: Zn(s)→Zn+2+2e- ;E˚=0.76V & Ag(s) → Ag+ + e- ; E˚ = -0.80V Which of the following reactions actually will take place? (i) Zn(s) + 2Ag+(aq) → Zn+2(aq) + 2Ag(s) (ii) Zn+2(aq) + 2Ag(s) → 2Ag+(aq) + Zn(s) (iii) Zn(s) + Ag(s) → Zn+2(aq) + Ag+(aq) (iv) Zn+2(aq) + Ag+(aq) → Zn(s) + Ag(s). 43. If the half cell reaction, A + e- → A- has a large negative reduction potential, it follows that, (i) A is readily reduced (ii) A is readily oxidized (iii) A- is readily reduced (iv) A- is readily oxidized. 44. The standard EMF of the cell reaction, Zn(s) + Cu+2(aq) Cu(s) + Zn+2(aq) is 1.10V at 25˚C. The EMF for the cell reaction when 0.1M Cu+2 and 0.1M Zn+2 solutions are used at 25˚C is: (i) 1.10V (ii) 0.110V (iii) -1.10V (iv) -0.110V 45. The standard E˚red. Values of A, B and C are 0.68V, -2.54V and -0.50V, respectively. The order of their reducing power is: (i) A>B>C (ii) A>C>B (iii) C>B>A (iv) B>C>A 46. The standard reduction potentials of Li+/Li, Ba+2/Ba, Na+/Na and Mg+2/Mg are -3.05, -2.73, -2.71 and -2.37V, respectively. Which one of the following is strongest oxidizing agent? (i) Na+ (ii) Li+ (iii) Ba+2 (iv) Mg+2 ANSWERS Q. | Ans. | Q. | Ans. | Q. | Ans. | Q. | Ans. | Q. | Ans. | Q. | Ans. | Q. | Ans | 1. | 0.31V | 8. | 3.44 | 15. | 20.98 | 22. | Reaction | 29. | -0.8191V | 36 | 50mV | 43. | (iv) | 2. | 2.96V | 9. | 5.67 | 16. | Yes | 23. | 1.20V, Cd | 30 | -0.2795V | 37 | (ii) | 44. | (i) | 3. | 1.562V | 10. | -0.79V | 17. | 1.23x106 | 24. | 0.48V | 31 | 1.544V | 38 | (i) | 45. | (iv) | 4. | No | 11. | 1.53V | 18. | 3.27 | 25. | 1.562V | 32 | 0.7503V | 39 | (i) | 46. | (iv) | 5. | 1.81V | 12. | 1.32 V | 19. | 1.6x1037 | 26. | 1.48x10-9M | 33 | 1.103V | 40 | (i) | | | 6. | 0.8221V | 13. | 1x1052 | 20. | -0.8102V | 27 | 5.00 | 34 | 0.34V,0.31V | 41 | (ii) | | | 7. | 1.58955V | 14. | 1.585x1037 | 21. | 1.113V, Yes | 28. | Reaction | 35 | 0.039V | 42 | (i) | | |