Tiêu đề 17. Electrochemistry.pdf ✅

ELECTROCHEMISTRY 17 FACT/DEFINITION TYPE QUESTIONS 1. Which of the following statements is incorrect regarding electrochemistry? (a) It is the study of production of electricity from energy released during spontaneous chemical reactions. (b) NaOH, Cl2 , alkali and alkaline earth metals are prepared by electrochemical methods. (c) The demerit associated with electrochemical methods is that they are more polluting. Thus they are eco- destructive. (d) Electrochemical reactions are more energy efficient and less polluting. 2. What flows in the internal circuit of a galvanic cell? (a) Ions (b) Electrons (c) Electricity (d) Atoms 3. Which of the following statements about galvanic cell is incorrect (a) anode is positive (b) oxidation occurs at the electrode with lower reduction potential (c) cathode is positive (d) reduction occurs at cathode 4. Reaction that takes place at graphite anode in dry cell is (a) 2 Zn 2e Zn(s) o (b) 2 Zn(s) Zn 2e o (c) Mn 2e Mn(s) 2 o (d) Mn(s) Mn e 1.5V o 5. In which of the following conditions salt bridge is not required in a galvanic cell? (a) When galvanic cell is used in geyser. (b) When distance between oxidation half cell and reduction half cell is negligible. (c) Electrolytic solutions used in both the half cells are of same concentration. (d) When both the electrodes are dipped in the same electrolytic solution. 6. Which device converts chemical energy of a spontaneous redox reaction into electrical energy? (a) Galvanic cell (b) Electrolytic cell (c) Daniell cell (d) Both (a) and (c) 7. Which one is not called a anode reaction from the following? (a) 2 1 Cl Cl e 2 o (b) Cu Cu 2e o (c) Hg Hg e o (d) 2 Zn 2e Zn o 8. The cell reaction 2 Cu 2Ag Cu Ag o is best represented by (a) 2 Cu( ) | Cu ( ) || Ag ( ) | Ag( ) s aq aq s (b) 2 Pt | Cu || Ag ( ) | Ag( ) aq s (c) 2 Cu | Cu | | Pt | Ag (d) None of the above representations 9. 2 2 anode cathode Zn ( ) | Zn ( ) | | Cu ( ) |Cu( ) is s aq aq s (a) Weston cell (b) Daniel cell (c) Calomel cell (d) Faraday cell 10. The tendency of an electrode to lose electrons is known as (a) electrode potential (b) reduction potential (c) oxidation potential (d) e.m.f. 11. The chemical reaction, 2AgCl(s) H (g) 2HCl(aq) 2Ag(s) o 2 taking place in a galvanic cell is represented by the notation (a) Pt(s) | H (g),1 bar |1M KCl(aq) | AgCl(s) | Ag(s) 2 (b) Pt(s) | H (g),1 bar |1M HCl(aq) |1MAg (aq) | Ag(s) 2 (c) Pt(s) | H (g),1 bar |1MHCl(aq) | AgCl(s) | Ag(s) 2 (d) Pt(s) | H (g),1 bar |1MHCl(aq) | Ag(s) | AgCl(s) 2 12. Given that the standard reduction potentials for M+ /M and N+ /N electrodes at 298 K are 0.52 V and 0.25 V respectively. Which of the following is correct in respect of the following electrochemical cell ? M/M+ | | N+ /N (a) The overall cell reaction is a spontaneous reaction. (b) The standard EMF of the cell is – 0.27 V. (c) The standard EMF of the cell is 0.77 V. (d) The standard EMF of the cell is – 0.77 V.
276 ELECTROCHEMISTRY 13. The difference between the electrode potentials of two electrodes when no current is drawn through the cell is called _________. (a) Cell potentials (b) Cell emf (c) Potential difference (d) Cell voltage 14. For the given Nernst equation 2 cell cell 2 Mg RT E E ln 2F Ag a o ¬ 1⁄4 q a o ¬ 1⁄4 Which of the following representation is correct? (a) Ag+ |Ag||Mg2+|Mg (b) Mg2+|Mg||Ag|Ag+ (c) Mg|Mg2+||Ag+ |Ag (d) Mg|Mg2+||Ag|Ag+ 15. For cell representation: Cu(s)|Cu2+(aq)||Ag+ (aq)|Ag(s) Which of the following is correct? (i) Cu is reducing agent. (ii) Overall cell reaction is 2 Cu s 2Ag aq Cu aq 2Ag s o (iii) Cu is cathode (iv) Ag is anode (a) (ii), (iii) and (iv) (b) (ii), (iii) and (iv) (c) (iii) and (iv) (d) (i) and (ii) 16. The reference electrode is made by using (a) ZnCl2 (b) CuSO4 (c) HgCl2 (d) Hg2Cl2 17. The standard hydrogen electrode potential is zero, because (a) hydrogen oxidized easily (b) electrode potential is considered as zero (c) hydrogen atom has only one electron (d) hydrogen is a very light element 18. Without losing its concentration ZnCl2 solution cannot be kept in contact with (a) Au (b) Al (c) Pb (d) Ag 19. On the basis of the following E° values, the strongest oxidizing agent is : [Fe(CN)6 ] 4– o[Fe(CN)6 ] 3– + e– ; E° = – 0.35 V Fe2+ o Fe3+ + e– ; E° = – 0.77 V (a) [Fe(CN)6 ] 4– (b) Fe2+ (c) Fe3+ (d) [Fe(CN)6 ] 3– 20. Standard electrode potential of three metals X, Y and Z are – 1.2 V, + 0.5 V and – 3.0 V, respectively. The reducing power of these metals will be : (a) Y > Z > X (b) X > Y > Z (c) Z > X > Y (d) X > Y > Z 21. Standard electrode potential for Sn4+ / Sn2+ couple is + 0.15 V and that for the Cr3+ / Cr couple is – 0.74 V. These two couples in their standard state are connected to make a cell. The cell potential will be (a) + 1.19 V (b) + 0.89 V (c) + 0.18 V (d) + 1.83 V 22. Standard reduction potentials of the half reactions are given below : F2 (g) + 2e– o 2F– (aq); E° = + 2.85 V Cl2 (g) + 2e–o 2Cl– (aq); E° = + 1.36 V Br2 (l) + 2e– o 2Br– (aq); E° = + 1.06 V I 2 (s) + 2e–o 2I– (aq); E° = + 0.53 V The strongest oxidising and reducing agents respectively are (a) F2 and I– (b) Br2 and Cl– (c) Cl2 and Br– (d) Cl2 and I2 23. A button cell used in watches functions as following Zn(s) + Ag2O(s) + H2O(l) 2Ag(s) + Zn2+(aq) + 2OH– (aq) If half cell potentials are : Zn2+(aq) + 2e– o Zn(s); Eo = – 0.76 V Ag2O(s) + H2O (l) + 2e– o 2Ag(s) + 2OH– (aq); Eo = 0.34 V The cell potential will be : (a) 0.42 V (b) 0.84 V (c) 1.34 V (d) 1.10 V 24. The oxidation potentials of A and B are +2.37 and +1.66 V respectively. In chemical reactions (a) A will be replaced by B (b) A will replace B (c) A will not replace B (d) A and B will not replace each other 25. A smuggler could not carry gold by depositing iron on the gold surface since (a) gold is denser (b) iron rusts (c) gold has higher reduction potential than iron (d) gold has lower reduction potential than iron 26. Which cell will measure standard electrode potential of copper electrode ? (a) Pt (s) |H2 (g, 0.1 bar) |H+ (aq., 1 M) ||Cu2+ (aq., 1 M) | Cu (b) Pt (s) |H2 (g, 1 bar) |H+ (aq., 1 M) ||Cu2+ (aq., 2 M) | Cu (c) Pt (s) |H2 (g, 1 bar) |H+ (aq., 1 M) ||Cu2+ (aq., 1 M) | Cu (d) Pt (s) |H2 (g, 1 bar) |H+ (aq., 0.1 M) ||Cu2+ (aq., 1 M) | Cu 27. Which of the following statement is not correct about an inert electrode in a cell ? (a) It does not participate in the cell reaction. (b) It provides surface either for oxidation or for reduction reaction. (c) It provides surface for conduction of electrons. (d) It provides surface for redox reaction. 28. In the electrochemical reaction o 3 2 2 Fe2 ZnZn Fe2 , on increasing the concentration of Fe2+ (a) increases cell emf (b) increases the current flow (c) decreases the cell emf (d) alters the pH of the solution EduHulk ELECTROCHEMISTRY
ELECTROCHEMISTRY 277 29. The standard e.m.f. of a galvanic cell involving cell reaction with n = 2 is found to be 0.295 V at 25°C. The equilibrium constant of the reaction would be (Given F = 96500 C mol–1; R = 8.314JK–1mol–1) (a) 11 2.0u10 (b) 12 4.0u10 (c) 2 1.0u10 (d) 10 1.0u10 30. What will be the emf for the given cell Pt | H2 (P1 ) | H+ (aq) | | H2 (P2 ) | Pt (a) 1 e 2 log RT P F P (b) 1 2 log 2 e RT P F P (c) 2 e 1 log RT P F P (d) None of these 31. The value of electrode potential (10–4 M) H+ | H2 (1 atm) | Pt at 298 K would be (a) – 0.236 V (b) + 0.404 V (c) + 0.236 V (d) – 0.476 V 32. According to Nernst equation, which is not correct if Q = Kc : (a) Ecell = 0 (b) cell RT ln Q E nF D (c) nFEcell RT K e c D (d) Ecell cell E D 33. The standard emf of a cell, involving one electron change is found to be 0.591 V at 25°C. The equilibrium constant of the reaction is (F = 96500 C mol–1) (a) 1.0 × 101 (b) 1.0 × 105 (c) 1.0 × 1010 (d) 1.0 ×1030 34. For the galvanic cell Zn | Zn2+ (0.1M) || Cu2+ (1.0M)|Cu the cell potential increase if: (a) [Zn2+] is increased (b) [Cu2+] is increased (c) [Cu2+] is decreased (d) surface area of anode is increased 35. Consider the following cell reaction: 2 2 2 2Fe( ) O ( ) 4H ( ) 2Fe ( ) 2H O( );E 1.67V s g aq aq l o q At [Fe2+] = 10–3 M, p(O2 ) = 0.1 atm and pH = 3, the cell potential at 25oC is (a) 1.47 V (b) 1.77 V (c) 1.87 V (d) 1.57 V 36. The e.m.f. of a Daniell cell at 298 K is E1 . ZnSO CuSO 4 4 Zn Cu (0.01 M) (1.0 M) When the concentration of ZnSO4 is 1.0 M and that of CuSO4 is 0.01 M, the e.m.f. changed to E2 . What is the relationship between E1 and E2 ? (a) 2 E1 E 0 z (b) E1 ! E2 (c) E1 E2 (d) E1 E2 37. The electrode potential 2 (Zn Zn) E of a zinc electrode at 25°C with an aqueous solution of 0.1 M ZnSO4 is [ 2 (Zn Zn) E q = –0.76 V. Assume 2.303RT F = 0.06 at 298 K]. (a) + 0.73 (b) – 0.79 (c) – 0.82 (d) – 0.70 38. In the cell reaction 2 Cu(s) 2Ag (aq) Cu (aq) 2Ag(s) o , E o cell = 0.46 V. By doubling the concentration of Cu2+, Eo cell will become (a) doubled (b) halved (c) increases but less than double (d) decreases by a small fraction 39. E° of a cell aA bB ocC dD is (a) A B C D [a] [b] E RT ln [c] [d] (b) c d a b RT [C] [D] E ln nF [A] [B] (c) c D A B RT [C] [d] E ln nF [A] [B] (d) A B C D RT [a] [B] E ln nF [C] [d] 40. E° for the cell, 2 2 Zn | Zn (aq) | | Cu (aq)| Cu is 1.10 V at 25°C. The equilibrium constant for the cell reaction 2 Zn Cu (aq) 2 Cu Zn (aq) is of the order of (a) 10–37 (b) 1037 (c) 10–17 (d) 1017 41. What is the standard cell potential E° for an electrochemical cell in which the following reaction takes place spontaneously ? Cl (g) 2Br Br (aq) 2Cl G 50.6 kJ 2 2 o ' q (a) 1.2 V (b) 0.53 V (c) 0.26 V (d) –0.53 V 42. If 0.01 M solution of an electrolyte has a resistance of 40 ohms in a cell having a cell constant of 0.4 cm–1, then its molar conductance in ohm–1 cm2 mol–1 is (a) 102 (b) 104 (c) 10 (d) 103 43. Specific conductance of a 0.1 N KCl solution at 23oC is 0.012 ohm–1 cm–1. Resistance of cell containing the solution at same temperature was found to be 55 ohm. The cell constant is (a) 0.0616 cm–1 (b) 0.66 cm–1 (c) 6.60 cm–1 (d) 660 cm–1 44. The unit of equivalent conductivity is (a) ohm cm (b) ohm–1 cm2 (g equivalent)–1 (c) ohm cm2 (g equivalent) (d) S cm–2 EduHulk ELECTROCHEMISTRY
278 ELECTROCHEMISTRY 45. The resistance of 0.01 N solution of an electrolyte was found to be 220 ohm at 298 K using a conductivity cell with a cell constant of 0.88cm–1. The value of equivalent conductance of solution is – (a) 400 mho cm2 g eq–1 (b) 295 mho cm2 g eq–1 (c) 419 mho cm2 g eq–1 (d) 425 mho cm2 g eq–1 46. Specific conductance of 0.1 M HNO3 is 6.3×10–2 ohm–1 cm–1 . The molar conductance of the solution is (a) 100 ohm–1 cm2 (b) 515 ohm–1 cm2 (c) 630 ohm–1 cm2 (d) 6300 ohm–1 cm2 47. The specific conductance of a 0.1 N KCl solution at 23°C is 0.012 ohm–1cm–1. The resistance of cell containing the solution at the same temperature was found to be 55 ohm. The cell constant will be (a) 0.142 cm–1 (b) 0.66 cm–1 (c) 0.918 cm–1 (d) 1.12 cm–1 48. The unit of specific conductivity is (a) ohm cm–1 (b) ohm cm–2 (c) ohm–1 cm (d) ohm–1 cm–1 49. Which of the following solutions of KCl will have the highest value of specific conductance? (a) 1.0 N (b) 0.1 N (c) 1.0 ×10–2N (d) 1.0 ×10–3N 50. The cell constant of a conductivity cell ___________. (a) changes with change of electrolyte. (b) changes with change of concentration of electrolyte. (c) changes with temperature of electrolyte. (d) remains constant for a cell. 51. Which of the following pair(s) is/are incorrectly matched? (i) R (resistance) – ohm (:) (ii) U (resistivity) – ohm metre (:m) (iii) G (conductance) – seimens or ohm (S) (iv) N (conductivity) – seimens metre–1 (Sm–1) (a) (i), (ii) and (iii) (b) (ii) and (iii) (c) (i), (ii) and (iv) (d) (iii) only 52. On which of the following magnitude of conductivity does not depends? (a) Nature of material (b) Temperature (c) Pressure (d) Mass of the material 53. Which of the following expression correctly represents molar conductivity? (a) m K C (b) m KA l (c) m KV (d) All of these 54. Which of the following represents variation of molar conductance of electrolyte with (concentration)1⁄2 respectively for weak and strong electrolyte ? (i) m/(S cm mol ) 2 –1 1 2 c / (mol L) (ii) m/(S cm mol ) 2 –1 1 2 c / (mol L) (iii) 1 2 c / (mol L) m/(S cm mol ) 2 –1 (iv) m/(S cm mol ) 2 –1 1 2 c / (mol L) (v) 1 2 c / (mol L) m/(S cm mol ) 2 –1 Weak acid Strong acid (a) (iv) (v) (b) (ii) (iv) (c) (i) (ii) (d) (iii) (ii) 55. Electrolyte: KCl HCl NaOAc NaCl (S cm2 mol–1) : 149.9 145 426.2 91 126.5 KNO 3 f / Calculate HOAc f / using appropriate molar conductances of the electrolytes listed above at infinite dilution in OH2 at 25°C (a) 217.5 (b) 390.7 (c) 552.7 (d) 517.2 56. Kohlrausch’s law states that at (a) finite dilution, each ion makes definite contribution to equivalent conductance of an electrolyte, whatever be the nature of the other ion of the electrolyte. (b) infinite dilution each ion makes definite contribution to equivalent conductance of an electrolyte depending on the nature of the other ion of the electrolyte. (c) infinite dilution, each ion makes definite contribution to conductance of an electrolyte whatever be the nature of the other ion of the electrolyte. (d) infinite dilution, each ion makes definite contribution to equivalent conductance of an electrolyte, whatever be the nature of the other ion of the electrolyte. 57. Which of the following expressions correctly represents the equivalent conductance at infinite dilution of Al2 (SO4 ) 3 , Given that 3 Al /q and 2 SO4 /q are the equivalent conductances at infinite dilution of the respective ions? (a) 3 2 A 4 l SO 1 1 3 2 /q q / (b) 3 2 A 4 l SO 2 3 /q q / (c) 3 2 A 4 l SO /q q / (d) 3 2 A 4 l SO q q 6 § · / / u © 1 EduHulk ELECTROCHEMISTRY