Electrochemistry Exercise # 1

ELECTROCHEMISTRY Exercise # 1 1. 2. [Single Correct Choice Type Questions] The standard reduction potentials E° of the following systems are System E° (volts) MnO4¯ + 8H+ + 5e–  Mn2+ + 4H2O (i) 1.51 4+ – 2+ (ii) Sn + 2e  Sn 0.15 (iii) Cr2 O72– + 14H+ + 6e–  2Cr3+ + 7H2O 1.33 (iv) Ce4+ + e–  Ce3+ 1.61 The oxidising power of the various species decreases in the order (A) Ce4+ > Cr2 O72– > Sn4+ > MnO4¯ (B) Ce4+ > MnO4¯ > Cr2 O72– > Sn4+ (C) Cr2O72– > Sn4+ > Ce4+ > MnO4¯ (D) MnO4¯ > Ce4+ > Sn4+ > Cr2 O72– Consider the reaction : (T = 298 K) Cl2(g) + 2Br¯(aq)  2Cl¯ (aq) + Br2 (aq.) The emf of the cell, when [Cl¯] = [Br2] = [Br¯] = 0.01M and Cl2 gas is at 1 atm pressure, will be : (E° for the above reaction is = 0.29 volt) (A) 0.54 volt 3. 5. (D) –0.29 volt (B) 1.62 V (C) – 0.805 V (D) – 1.61 V Given : Eº(Cu2+ | Cu) = 0.337 V and Eº (Sn2+ | Sn) = – 0.136 V. Which of the following statements is correct? (A) Cu2+ ions can be reduced by H2(g) (B) Cu can be oxidized by H+ (C) Sn2+ ions can be reduced by H2(g) (D) Cu can reduce Sn2+ Red hot carbon will remove oxygen from the oxide AO and BO but not from MO, while B will remove oxygen from AO. The activity of metals A, B and M in decreasing order is (A) A > B > M 6. (C) 0.24 volt 2Ce4+ + Co  2Ce3+ + Co2+ Eºcell = 1.89 V, Eº Co2  / Co = – 0.277 V hence, Eº Ce4  / Ce3  is : (A) 0.805 V 4. (B) 0.35 volt (B) B > A > M What is the emf at 25° C for the cell, Ag (C) M > B > A AgBr (s), Br¯ a = 0.34 , Fe3+ , Fe2+ a = 0.1 a = 0.02 (D) M > A > B Pt The standard reduction potentials for the half-reactions AgBr + e¯  Ag + Br¯ and Fe3+ + e¯  Fe2+ are + 0.0713 V and + 0.770 V respectively. (A) 0.474 volt 7. (B) 0.529 volt (C) 0.356 volt (D) 0.713 volt MnO4– + 8H+ + 5e–  Mn2+ + 4H2O ; Eº = 1.51 V ; G10 = – 5 × 1.51 × F MnO2 + 4H+ + 2e–  Mn2+ + 2H2O ; Eº = 1.23 V ; G02 = – 2 × 1.23 × F Eº MnO – | MnO is 4 2 (A) 1.70 V (B) 0.91 V (C) 1.37 V (D) 0.548 V 8. A hydrogen electrode placed in a buffer solution of CH3COONa and CH3COOH in the ratios of x : y and y : x has electrode potential values E1 volts and E2 volts, respectively at 25ºC. The pKa values of acetic acid is (E1 and E2 are oxidation potentials) (A) 9. E1 + E 2 0.118 (B) E 2 – E1 0.118 (C) – E1 + E 2 0.118 (D) E1 – E 2 0.118 The electrode potential of electrode M (s)  Mn+ (aq) (2M) + ne–. at 298 K is E1. When temperature is doubled and concentration is made half, then the electrode potential becomes E2. Which of the following represents the correct relationship between E1 and E2 ? (A) E1 > E2 10. 12. (C) E1 = E2 (D) Can’t be predicted During the preparation of H2S2O8 (per disulphuric acid) O2 gas also releases at anode as byproduct, When 9.72 L of H2 releases at cathode and 2.35 L O2 at anode at STP, the weight of H2S2O8 produced in gram is (A) 87.12 11. (B) E1 < E2 (B) 43.56 (C) 83.42 (D) 51.74 The equivalent conductivity of KCl at infinite dilution is 130 S cm2 eq–1. The transport number of Cl–1 ion in KCl at the same temperature is 0.505. The limiting ionic mobility of K+ ion, is (A) 6.67 × 10–4 cm2 sec–1 volt–1 (B) 5.01 × 10–3 cm2 sec–1 volt–1 (C) 3.22 × 10–4 cm2 sec–1 volt–1 (D) 2.00 × 10–4 cm2 sec–1 volt–1 When the sample of copper with zinc impurity is to be purified by electrolysis, the appropriate electrode are (A) pure zinc as cathode and pure copper as anode (B) impure sample as cathode and pure copper as anode (C) impure zinc as cathode and impure sample as anode (D) pure copper as cathode and impure sample as anode 13. Two weak acid solutions HA1 and HA2 each with the same concentration and having pKa values 3 and 5 are placed in contact with hydrogen electrode (1 atm, 25ºC) and are interconnected through a salt bridge. The emf of the cell is : (A) 0.21 V 14. S nF (D) 0.021 V (B) nF S (C) – 2.303 RT log KC (D) –2.303 RT nF Electrolysis of a solution of MnSO4 in aqueous sulphuric acid is a method for the preparation of MnO2. Passing a current of 27A for 24 hours gives 1kg of MnO2. The current efficiency in this process is : (A) 100% 16. (C) 0.018 V G is the available energy (energy produced) during the electrochemical reaction in galvanic cell which can be converted into useful work. In the light of second law of thermodynamics in the cell the change in electrode potential with temperature will be equal to (A) 15. (B) 0.059 V (B) 95.185% (C) 80% (D) 82.951% The reduction potential of hydrogen electrode when placed in a buffer solution is found to be – 0.413V. The pH of the buffer is (A) 10 (B) 4 (C) 7 (D) 12 ELECTROCHEMISTRY 17. A galvanic cell is composed of two hydrogen electrodes, one of which is a standard one. In which of the following solutions should the other electrode be immersed to get maximum emf ? Ka (CH3COOH) = 2 × 10–5 , Ka (H3PO4) = 10–3 . (A) 0.1 M HCl (B) 0.1 M CH3COOH (C) 0.1 M H3PO4 (D) 0.1 M H2SO4 18. A gas Cl2 at 1 atm is bubbled through a solution containing a mixture of 1 M Br–1 and 1 M F–1 at 25ºC. If the reduction potential is F > Cl > Br, then : (A) Cl will oxidise Br and not F (B) Cl will oxidise F and not Br. (C) Cl will oxidise both Br and F (D) Cl will reduce both Br and F 19. Pure water is saturated with pure solid AgCl, a silver electrode is placed in the solution and the potential is measured against normal calomel electrode at 25°C. This experiment is then repeated with a saturated solution of AgI. If the difference in potential in the two cases is 0.177V. What is the ratio of solubility product (solubility) of AgCl and AgI at the temperature of the experiment ? (A) 103 (B) 106 (C) 102 (D) 102 The two aqueous solutions; A (AgNO3) and B(LiCl) were electrolysed using Pt. electrodes. The pH of the resulting solutions will (A) increase in A and decrease in B (B) decrease in both (C) increase in both (D) decrease in A and increase in B. 20. 21. When iron is rusted, it is : (A) reduced (B) oxidised (C) evaporated (D) decomposed 22. The oxidation potentials of Zn, Cu, Ag, H2 and Ni are 0.76, –0.34, –0.80, 0.00, 0.25 volt, respectively. Which of the following reactions will provide maximum voltage ? (A) Zn + Cu2+  Cu + Zn2+ (B) Zn + 2Ag+  2Ag + Zn2+ 2+ + (C) H2 + Cu  2H + Cu (D) H2 + Ni2+  2H+ + Ni 23. The reduction potential of a half-cell consisting of a Pt electrode immersed in 1.5 M Fe2+ and 0.015 M Fe3+ solution  0 at 25°C is E Fe3+ Fe2+  = 0.770 V . (A) 0.652 V (B) 0.88 V (C) 0.710 V (D) 0.850 V 2+ 24. Zn + Cu2+(aq) Cu + Zn2+(aq) Reaction quotient is Q = [Zn ] . Eºcell = 1.10 V. Ecell will be 1.1591 V when: [Cu 2+ ] A Ecell O (A) [Cu2+]/[Zn2+] = 0.01 (C) [Zn2+]/[Cu2+] = 0.1 25. log Q (B) [Zn2+]/[Cu2+] = 0.01 (D) [Zn2+]/[Cu2+] = 1 Which statement is correct. (A) In SHE, the pressure of dihydrogen gas should be low and pH of solution should be zero. (B) In the reaction H2O2 + O3  2H2O + 2O2, H2O2 is oxidised to H2O. (C) The absolute value of electrode potential cannot be determined. (D) According to IUPAC conventions, the standard electrode potential pertains to oxidation reactions only. (A) (B) Conductance Conductance measurements can be used to detect the end point of acid-base titrations. Which of the following plots correctly represent the end point of the titration of strong acid and a strong base ? Conductance 26. end point end point Volume of base added (D) Conductance Conductance (C) Volume of base added end point end point Volume of base added Volume of base added 27. Using the standard potential values given below, decide which of the statements I, II, III, IV are correct. Choose the right answer from (A), (B), (C) and (D) Fe2+ + 2e– = Fe, Eº = – 0.44 V 2+ – Cu + 2e = Cu, Eº = + 0.34 V Ag+ + e– = Ag, Eº = + 0.80 V I. Copper can displace iron from FeSO4 solution II. Iron can displace copper from CuSO4 solution III. Silver can displace Cu from CuSO4 solution IV. Iron can displace silver from AgNO3 solution (A) I and II (B) II and III (C) II and IV (D) I and IV 28. Four moles of electrons were transferred from anode to cathode in an experiment on electrolysis of water. The total volume of the two gases (dry and at STP) produced will be approximately (in litres) (A) 22.4 (B) 44.8 (C) 67.2 (D) 89.4 29. The standard reduction potential of a silver chloride electrode is 0.2 V and that of a silver electrode is 0.79 V. The maximum amount of AgCl that can dissolve in 106 L of a 0.1 M AgNO3 solution is (A) 0.5 mmol (B) 1.0 mmol (C) 2.0 mmol (D) 2.5 mmol 30. A cell Cu | Cu++ || Ag+ | Ag initially contains 2M Ag+ and 2M Cu++ ions in 1L electrolyte. The change in cell potential after the passage of 10 amp current for 4825 sec is : (A) – 0.00738 V (B) – 1.00738 V (C) – 0.0038 V (D) none 31. When the electric current is passed through a cell having an electrolyte, the positive ions move towards cathode and negative ions towards the anode. If the cathode is pulled out of the solution (A) the positive and negative ions will move towards anode (B) the positive ions will start moving towards the anode while negative ions will stop moving (C) the negative ions will continue to move towards anode while positive ions will stop moving (D) the positive and negative ions will start moving randomly ELECTROCHEMISTRY 32. Which one of the following will increase the voltage of the cell ? (T = 298 K) Sn + 2Ag+  Sn2+ + 2Ag (A) increase in the size of silver rod (C) increase in the concentration of Ag+ ions 33. (B) increase in the concentration of Sn+2 ions (D) none of the above In a H2 – O2 fuel cell, 6.72 L of hydrogen at NTP reacts in 15 minutes, the average current produced in amperes is (A) 64.3 amp (B) 643.3 amp (C) 6.43 amp (D) 0.643 amp 34. With t taken in seconds and  taken in Amp, the variation of  follows the equation t2 + 2 = 25 what amount of Ag will be electrodeposited with this current flowing in the interval 0–5 second ? (Ag – 108) (A) 22 mg (B) 66 mg (C) 77 mg (D) 88 mg 35. Acetic acid is titrated with NaOH solution. Which of the following statement is correct for this titration? (A) conductance increases upto equivalence point, then it decreases (B) conductance increases upto equivalence point, then it increases (C) first conductance increases slowly upto equivalence point and then increases rapidly (D) first conductance increases slowly upto equivalence point and then drops rapidly . 36. Which statement is correct. (A) A solution of copper (II) sulphate can be stored in iron vessel. (B) An oxide layer on zinc vessel can be easily removed by washing with dilute HCl. (C) Molten PbBr2 is good conductor of electricity because it contains free ions. 1 H  LiH, hydrogen is a reducing agent. 2 2 During the electrolysis of 0.1 M CuSO4 solution using copper electrodes, a depletion of [Cu++] occurs near the cathode with a corresponding excess near the anode, owing to inefficient stirring of the solution. If the local concentrations of [Cu++] near the anode & cathode are respectively 0.12 M & 0.08 M, calculate the back e.m.f. developed . Temperature = 298 K . (A) 22 mV (B) 5.2 mV (C) 29 mV (D) 59 mV (D) In the reaction, Li + 37. 38. How much the potential of a hydrogen electrode will change when its solution initially at pH = 0 is neutralised to pH = 7? (A) Increase by 0.059 V (B) Decrease by 0.059 V (C) Increase by 0.41 V (D) Decrease by 0.41 V 39. The standard electrode potentials (reduction) of Pt/Fe2+ , Fe3+ and Pt/Sn4+, Sn2+ are + 0.77 V and 0.15 V respectively at 25° C. The standard EMF of the reaction Sn4+ + 2Fe2+  Sn2+ + 2Fe3+ is (A) – 0.62 V (B) – 0.92 V (C) + 0.31 V (D) + 0.85 V 40. An acidic solution of copper () sulphate containing some contaminations of zinc and iron () ions was electrolysed till all the copper is deposited. If electrolysis is further continued for sometime, the product liberated at cathode would be : (A) Fe (B) Zn (C) H2 (D) Alloy of Zn and Fe. 41. Consider the following Galvanic cell as shown in figure. By what value the cell voltage change when concentration of ions in anode and cathodic compartments both increased by factor of 10 at 298 K (A) + 0.591 (C) – 0.1182 (B) – 0.0591 (D) 0 Voltmeter H2 (g) Cl2(g) + K NO3 Pt(s) HCl Anode + HCl Cathode 42. Pt | Cl2 (P1 atm) | HCl (0.1 M) | Cl2 (P2 atm) | Pt, cell reaction will be spontaneous if (A) P1 = P2 (B) P1 > P2 (C) P2 > P1 (D) P1 = P2 = 1 atm 43. Pt (H2) | pH = 2 | pH = 3 | Pt (H2) 1 atm 1 atm The cell reaction for the given cell is (A) spontaneous (B) non-spontaneous (C) equilibrium (D) None of these 44. Equivalent conductance of 1M CH3COOH is 10 ohm–1 cm2 equiv–1 and that at infinite dilution is 200 ohm–1 cm2, equiv–1. Hence % ionisation of CH3COOH is : (A) 5% (B) 2% (C) 4% (D) 1% 45. Adding powdered Pb and Fe to a solution containing 1.0 M is each of Pb2+ and Fe2+ ions would result into the formation of (A) More of Pb and Fe2+ ions (B) More of Fe and Pb2+ ions (C) More of Fe and Pb (D) More of Fe2+ and Pb2+ ions 46. Cost of electricity for the production of 'X' litre H2 at NTP at cathode is Rs. X, then cost of electricity for the production 'X' litre O2 gas at NTP at anode will (assume 1 mole of electrons as one unit of electricity) (A) 2X (B) 4X (C) 16X (D) 32X + – 47. In the given figure the electrolytic cell contains 1 L of an aqueous 1 M Copper (II) sulphate solution. If 0.4 mole of electrons passed through of cell, the concentration of copper ion after passage of the charge will be – (A) 0.4 M 48. – e (B) 0.8 M e Cu Cu CuSO4 (C) 1.0 M (D) 1.2 M By how much will the potential of half cell Cu2+ / Cu change if the solution is diluted to 100 times at 298 K (A) Increases by 59 mV (B) Decreases by 59 mV (C) Increases by 29.5 mV (D) Decreases by 29.5 mV 49. Which of the following facts is not true ? (A) If Eº (Mn+ / M) is negative, H+ will be reduced to H2 by the metal M (B) If Eº (Mn+ / M) is positive, Mn+ will be reduced to M by H2 (C) In a cell Mn+ / M electrode is attached to hydrogen-half cell. To produce spontaneous cell reaction, metal M will act as negative electrode. (D) Compounds of active metals (Zn, Na, Mg) are reducible by H2 whereas those of noble metals (Cu, Ag, Au) are not reducible. 50. The reaction Zn(s) + 2AgCl(g)  ZnCl2(aq) + 2Ag(s) occurs in the cell Zn |ZnCl2 (1M solution), AgCl(s) | Ag. The number of Faradays required from the external source for this reaction to occur in the cell is (A) 2 (B) 3 (C) 1 (D) zero 51. If the pressure of hydrogen gas is increased from 1 atm. to 100 atm, keeping the hydrogen ion concentration constant at 1M, the reduction potential of the hydrogen half cell is at 25°C will be (A) 0.059 V (B) – 0.059 V (C) 0.295 V (D) 0.118 V 52. The equilibrium Cu++ (aq) + Cu(s) 2Cu+ established at 20°C corresponds to [Cu ++ ] = 2.02 × 104+ . The standard [Cu + ]2 potential, E 0   = 0.33 volt at this temperature. What is the standard potential, E 0 Cu ,Cu Cu / Cu  (A) – 0.457 V (B) – 0.125 V (C) – 0.66 V ? (D) – 0.250 V ELECTROCHEMISTRY 53. Zn Amalgam is prepared by electrolysis of aqueous ZnCl2 using Hg cathode (9gm). How much current is to be passed through ZnCl2 solution for 1000 seconds to prepare a Zn Amalgam with 25% Zn by wt. (Zn = 65.4) (A) 5.6 amp (B) 7.2 amp (C) 8.85 amp (D) 11.2 amp 54. A solution containing one mol per litre each of Cu(NO3)2, AgNO3, Hg(NO3)2 and Mg(NO3)2 is being electrolysed by using inert electrodes. The values of the standard oxidation potentials in volts are Ag/Ag+ = –0.8 V ; Hg/Hg2+ = – 0.79 V; Cu/Cu2+ = – 0.34 V ; Mg/Mg2+ = 2.37 V. The order in which metals will be formed at cathode will be (A) Ag, Cu, Hg, Mg (B) Ag, Hg, Cu, Mg (C) Ag, Hg, Cu (D) Cu, Hg, Ag 55. At 298K the standard free energy of formation of H2O() is –237.20 kJ/mole while Gº of its ionisation into H+ ion and hydroxyl ions is 80 kJ/mole, then the emf of the following cell at 298 K will be H2(g,1 bar) | H+ (1M) || OH¯ (1M) | O2 (g, 1bar) (A) 0.40 V (B) 0.81 V (C) 1.23 V (D) –0.40 V ClO3 56. – 0.54 V – ClO 0.45 V 1.07V 1 2 Cl2 – Cl 0.76 V 57. The E° in the given figure is, E° (A) 0.5 (B) 0.6 (C) 0.7 (D) 0.8 What is cell entropy change of the following cell ? Pt(s) | H2 (g) | CH3COOH, HCl || KCl (aq) | Hg2Cl2 (s) | Hg P = 1 atm 0.1M 0.1M Emf of the cell is found to be 0.045 V at 298 K and temperature coefficient is 3.4 × 10 –4 V K–1 58. Given K a (CH3COOH) = 10–5 M (A) 60 (B) 65.2 (C) 69.2 (D) 63.5 Na-amalgam is prepared by electrolysis of NaCl solution using liquid Hg as cathode. How long should the current of 10 amp. is passed to produce 10% Na – Hg on a cathode of 10 gm Hg. (atomic mass of Na = 23). (A) 7.77 min (B) 9.44 min. (C) 5.24 min. (D) 11.39 min. 59. Which of following cell can produce more electrical work. (A) Pt, H2 |0.1M NH4Cl || 0.1 M CH3COOH | H2, Pt (B) Pt, H2 | 0.1 M HCl || 0.1 M NaOH | H2, Pt (C) Pt, H2 | 0.1 M HCl || 0.1 M CH3COOK | H2, Pt (D) Pt, H2 | 0.1 M CH3COOK || 0.1 M HCl | H2, Pt 60. A hydrogen electrode is immersed in a solution with pH = 0 (HCl). By how much will the potential (reduction) change if an equivalent amount of NaOH is added to the solution. (Take pH2 = 1 atm) T = 298 K. (A) increase by 0.41V (B) increase by 59 mV (C) decrease by 0.41V (D) decrease by 59 mV 61. A current of 0.1A was passed for 2hr through a solution of cuprocyanide and 0.3745 g of copper was deposited on the cathode. Calculate the current efficiency for the copper deposition. (Cu – 63.5) (A) 79% B) 39.5 % (C) 63.25% (D) 63.5% 62. A current is passed through 2 voltameters connected in series. The first voltameter contains XSO4 (aq.) and second has Y2SO4 (aq.). The relative atomic masses of X and Y are in the ratio of 2 : 1. The ratio of the mass of X liberated to the mass of Y liberated is (A) 1 : 1 (B) 1 : 2 (C) 2 : 1 (D) None of the above 63. Which of the following is not true about e.m.f. of a cell ? (A) work calculated from it is not the maximum work obtainable from the cell (B) it is maximum voltage obtainable from the cell (C) it is the potential difference between two electrodes when no current is flowing in circuit (D) it is responsible for the flow of steady current in the cell. 64. How many electrons are delivered at the cathode during electrolysis by a current of 1amp in 60 seconds? (A) 3.74 × 1020 (B) 6.0 × 1023 (C) 7.48 × 1021 (D) 6.0 × 1020 65. A resistance of 50 is registered when two electrodes are suspended into a beaker containing a dilute solution of a strong electrolyte such that exactly half of the them are submerged into solution as shown in figure. If the solution is diluted by adding pure water (negligible conductivity) so as to just completely submerge the electrodes, the new resistance offered by the solution would be (A) 50  (B) 100  (C) 25  (D) 200  66. Calculate the cell EMF in mV for Pt  H2 (1atm)  HCl (0.01 M)  AgCl(s)  Ag(s) at 298 K if Gf° values are at 25°C – 109.56 kJ/mol for AgCl(s) and – 130.79 kJ/mol for (H+ + Cl– ) (aq) (A) 456 mV (B) 654 mV (C) 546 mV (D) None of these 67. Calculate the value of  m  for SrCl2 in water at 25ºC from the following data : Conc. (mol/lt) 0.25 1 m (–1 cm2 mol–1) 260 250 (A) 270 (B) 260 (C) 250 68. 69. 70. 71. (D) 255 BY the electrolysis of aqueous solution of CuSO4, the products obtained at both the electrodes are (A) O2 at anode and H2 at cathode (B) H2 at anode and Cu at cathode (C) O2 at anode and Cu at cathode (D) H2S2O8 at anode and O2 at cathode How many gm of silver will be displaced from a solution of AgNO3 by 4 gm of magnesium? (A) 18 gm (B) 4 gm (C) 36 gm (D) 16 gm The moles of electrons required to deposit 1 gm equivalent aluminium (at. wt. = 27) from a solution of aluminium chloride will be : (A) 3 (B) 1 (C) 4 (D) 2 A certain current liberated 0.504 g of hydrogen in 2 hours. How many grams of copper can be liberated by the same current flowing for the same time in copper sulphate solution (A) 31.8 g (B) 16.0 g (C) 12.7 g (D) 63.5 g 72. The specific conductance of a N/10 KCl at 25°C is 0.0112 ohm–1 cm–1. The resistance of cell containing solution at the same temperature was found to be 55 ohms. The cell constant will be (A) 6.16 cm–1 (B) 0.616 cm–1 (C) 0.0616 cm–1 (D) 616 cm–1 73. Which of the following statements is true for an electrochemical cell of Cu–H2. (A) H2 is anode and Cu is cathode (B) H2 is cathode and Cu is anode (C) reduction occurs at H2 electrode (D) oxidation occurs Cu electrode How many electrons flow when a current of 5 amperes is passed through a conductor for 200 seconds? (A) 6.214 × 1021 (B) 6.0241 × 1021 (C) 6.241 × 1022 (D) 6.0241 × 1022 74. 75. 76. A current of 9.95 amp following for 10 minutes, deposits 3 gm of a metal. Equivalent weight of the metal is (A) 12.5 (B) 18.5 (C) 21.5 (D) 48.5 Which of the following has been universally accepted as a reference electrode at all temperatures and has been assigned a value of zero volt? (A) platinum electrode (B) copper electrode (C) graphite electrode (D) standard hydrogen electrode ELECTROCHEMISTRY 77. What is the amount of chlorine evolved, when 2 amp of current is passed for 30 minutes in an aqueous solution of NaCl? (A) 9.81 g 78. (B) 1.32 g (C) 4.56 g (D) 12.6 g (C) electrolyte (D) none of these A spoon to be electroplated with gold it should be : (A) cathode (B) anode 79. Time required to deposit one millimole of aluminium metal by the passage of 9.65 amperes through aqueous solution of aluminium ion is : (A) 30 s (B) 10 s (C) 30,000 s (D) 10,000 s 80. During an electrolysis of conc. H2SO4, perdisulphuric acid (H2S2O8) and O2 form in equimolar amount. The amount of H2 that will form simultaneously at other electrode will be (2H2SO4  H2S2O8 + 2H+ + 2e–) (A) thrice that of O2 in moles (B) twice that of O2 in moles (C) equal to that of O2 in moles (D) half of that of O2 in moles 81. The electric charge for electrode deposition of one gram equivalent of a substance is : (A) one amp /sec (B) 96,500 C / sec (C) one amp / hour (D) 96,500 C 82. A solution of sodium sulphate in water is electrolysed using inert electrodes. The products at the cathode and anode are respectively. (A) H2, O2 (B) O2, H2 (C) O2, Na (D) O2, SO2 Which of the following statements is true for the electrochemical, Daniel cell ? (A) Electrons flows from copper electrode to zinc electrode. (B) Current flows from zinc electrode to copper electrode. (C) Cations moves toward copper electrode. (D) Cations moves toward zinc electrode 83. 84. The chemical reaction 2AgCl(s) + H2 (g)  2HCl (aq) + 2Ag (s) taking place in a galvanic cell is represented by the notation. (A) Pt(s) | H2 (g), 1 bar | 1 M KCl (aq) | AgCl(s) | Ag (s) (B) Pt(s) | H2 (g), 1 bar | 1 M HCl (aq) | 1 M Ag+ (aq) | Ag (s) (C) Pt(s) | H2 (g), 1 bar | 1 M HCl (aq) | AgCl (s) | Ag (s) (D) Pt(s) | H2 (g), 1 bar | 1 M HCl (aq) | Ag (s) | AgCl (s) 85. For the cell (at 298 K) Ag(s) | AgCl(s) | Cl– (aq) || AgNO3 (aq) | Ag(s) Which of following is correct (A) The cell emf will be zero when [Ag+]a = [Ag+]c ([Ag+] in anodic compartment = [Ag+] in cathodic compartment) (B) The amount of AgCl(s) precipitate in anodic compartment will decrease with the working of the cell. (C) The concentration of [Ag+] = constant, in anodic compartment during working of cell. (D) Ecell = E 0Ag + |Ag – E 0Cl– | AgCl | Ag – 86. 0.059 1 log 1 [Cl ]a The standard oxidation potentials, Eº, for the half reactions are as Zn  Zn2+ + 2e– ; E0 = + 0.76 V Fe  Fe2+ + 2e– ; E0 = + 0.41 V The EMF for the cell : (A) –0.35 V (B) + 0.35 V (C) + 1.17 V (D) – 1.17 V EXERCISE - 1 1. B 2. B 3. B 4. A 5. C 6. D 7. A 8. A 9. B 10. B 11. A 12. D 13. B 14.  15. B 16. C 17. B 18. A 19. A 20. D 21. B 22. B 23. A 24. B 25. C 26. A 27. C 28. C 29. B 30. A 31. D 32. C 33. A 34. A 35. C 36. C 37. B 38. D 39. A 40. C 41. C 42. C 43. B 44. A 45. A 46. A 47. C 48. B 49. D 50. D 51. B 52. A 53. C 54. C 55. A 56. B 57. B 58. A 59. D 60. C 61. A 62. A 63. A 64. A 65. A 66. A 67. A 68. C 69. C 70. A 71. C 72. C 73. A 74. A 75. D 76. D 77. B 78. A 79. B 80. A 81. D 82. A 83. C 84. B 85. A 86. B