Allen Career Institute Pre-Medical Chemistry Past Paper PDF

Chemistry Pre-Medical ©...

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Exercise-III (Analytical Questions) 155 02 :2 n io ss Se NEET SYLLABUS Electrochemistry : Conductance in electrolytic solutions, specific and molar conductivity variation of conductivity with concentration, Kohlrausch’s Law, Galvanic cells, Redox reactions, EMF of a cell, standard electrode potential, Relation between Gibbs energy change and EMF of a cell, electrolysis and electrolytic cells, Laws of electrolysis (elementary idea), dry cell, lead accumulator, fuel cells, corrosion.  ® 144 Pre-Medical : Chemistry ALLEN EXERCISE-I (Conceptual Questions) Build Up Your Understanding ELECTROLYTIC CONDUCTANCE 8. Which statement is not correct :– (1) Conductance of an electrolytic solution increases 1. Strong electrolytes are those which : with dilution (1) dissolve readily in water (2) Conductance of an electrolytic solution decreases (2) conduct electricity with dilution (3) dissociate into ions even at high concentration (3) Specific conductance of an electrolytic solution (4) dissociate into ions at high dilution. decreases with dilution EC0001 (4) Equivalent conductance of an electrolytic solution increases with dilution. 2. Molten sodium chloride conducts electricity due to EC0011 the presence of : (1) free electrons 9. The resistance of 0.01 N solution of an electrolyte (2) free ions was found to be 210 ohm at 298 K using a (3) free molecules conductivity cell of cell constant 0.66 cm–1. The (4) free atoms of Na and Cl equivalent conductance of solution is :– EC0002 3. Electrolytic conduction is due to the movement of : (1) 314.28 mho cm2 eq–1 (1) molecules (2) atoms (2) 3.14 mho cm2 eq–1 (3) ions (4) electrons (3) 314.28 mho–1 cm2 eq–1 EC0003 4. Which of the following solutions of KCl has the lowest (4) 3.14 mho–1 cm2 eq–1 value of equivalent conductance ? EC0012 (1) 1 M (2) 0.1 M 10. Electrolytic conduction differs from metallic 21 (3) 0.01 M (4) 0.001 M conduction from the fact that in the former 0- EC0004 5. If the specific resistance of a solution of concentration (1) The resistance increases with increasing 02 C geq L–1 is R, then its equivalent conductance is : temperature :2 100R RC (2) The resistance decreases with increasing (1) (2) n C 1000 temperature io (3) The resistance remains constant with increasing ss 1000 C (3) (4) temperature Se RC 1000R EC0006 (4) The resistance is independent of the length of 6. The specific conductances in ohm cm–1 of four –1 the conductor Z:\NODE02\B0B0-BA\TARGET\CHEM\ENG\MODULE-4\4.ELECTROCHEMISTRY\02-EXE.P65 electrolytes P, Q, R and S are given in brackets : EC0013 P (5.0 × 10–5) Q (7.0 × 10–8) 11. The specific conductance of a 0.01 M solution of R (1.0 × 10 )–10 S (9.2 × 10–3) KCl is 0.0014 ohm–1 cm–1at 25° C. Its equivalent The one that offers highest resistance to the passage conductance (cm2 ohm–1 eq–1) is :– of electric current is (1) 140 (2) 14 (1) P (2) S (3) R (4) Q EC0007 (3) 1.4 (4) 0.14 7. The specific conductance of a salt of 0.01 M EC0014 concentration is 1.061 × 10–4 S cm–1. Molar 12. Which one of the following is wrong :– conductance of the same solution will be : (1) Specific conductance increases on dilution. (1) 1.061 × 10 –4 S cm2 mol–1 (2) Specific conductance decreases on dilution. (2) 1.061 S cm2 mol–1 (3) Equivalent conductance increases on dilution. (3) 10.61 S cm2 mol–1 (4) Molar conductance increases on dilution. (4) 106.1 S cm2 mol–1 EC0008 EC0015 E  ® ALLEN Pre-Medical : Chemistry 145 KOHLRAUSCH LAW (4) Infinite dilution, each ion makes definite contribution to equivalent conductance of an 13. At infinite dilution, the equivalent conductances of electrolyte depending on the nature of the other CH3COONa, HCl and CH3COOH are 91, 426 and ion of electrolyte. 391 mho cm2 eq–1 respectively at 25 °C. The eq. EC0099 conductance of NaCl at infinite dilution will be : (1) 126 (2) 209 (3) 391 (4) 908 GALVANIC CELL EC0016 19. In the galvanic cell 14. For HCl solution at 25 °C, equivalent conductance Cu(s) |Cu2+ (1 M) || Ag+ (1 M) | Ag(s) at infinite dilution is 425 ohm–1 cm2 eq–1. The the electrons will travel in the external circuit : specific conductance of a solution of HCl is (1) from Ag to Cu 3.825 ohm–1 cm–1. If the degree of dissociation is 90%, the normality of the solution is :- (2) from Cu to Ag (1) 0.90 N (2) 1.0 N (3) electrons do not travel in the external circuit (3) 10 N (4) 1.2 N (4) in any direction EC0019 EC0023 15. The molar conductivities Ù0NaOAc and Ù0HCl at infinite 20. The direction of current in the Daniell cell when Zn and Cu electrodes are connected is : dilutio n in wat er a t 25°C are 91.0 and 426.2 S cm2 mol–1 respectively. To calculate Ù0HOAc (1) from Cu to Zn in the cell the additional value required is : (2) from Cu to Zn out side the cell 0 (3) from Zn to Cu outside the cell (1) Ù 0NaCl (2) Ù H2O (3) Ù0KCl (4) Ù0NaOH (4) in any direction in the cell 21 EC0020 EC0024 0- 16. The molar conductance of AgNO3, AgCl and NaCl 21. The equation representing the process by which 02 at infinite dilution are 116.5, 121.6 and 110.3 S cm 2 mol –1 respectively. The molar standard reduction potential of zinc can be defined is :2 conductance of NaNO3 is : (1) Zn2+ (s) + 2e– ¾¾® Zn (s) (1) 111.4 S cm2 mol–1 (2) 105.2 S cm2 mol–1 n (2) Zn (g) ¾¾® Zn2+ (g) + 2e– io (3) 130.6 S cm mol 2 –1 (4) 150.2 S cm mol 2 –1 (3) Zn2+ (g) + 2e– ¾¾® Zn (s) ss EC0021 (4) Zn2+ (aq.) + 2e– ¾¾® Zn (s) Se 17. The conductivity of a saturated solution of BaSO4 is 3.06 × 10–6 ohm–1 cm–1and its molar conductance EC0025 is 1.53 ohm–1 cm2 mol–1. The Ksp of BaSO4 will be 22. A standard hydrogen electrode has zero electrode Z:\NODE02\B0B0-BA\TARGET\CHEM\ENG\MODULE-4\4.ELECTROCHEMISTRY\02-EXE.P65 (1) 4 × 10 –12 (2) 2.5 × 10 –9 potential because : (3) 2.5 × 10–13 (4) 4 × 10–6 (1) Hydrogen is easiest to oxidize. EC0022 (2) This electrode potential is assumed to be zero. 18. Kohlrausch's law states that at :- (3) Hydrogen atom has only one electron. (1) Infinite dilution, each ion makes definite (4) Hydrogen is the lightest element. contribution to conductance of an electrolyte EC0026 whatever be the nature of the other ion of the electrolyte. 23. Which is not true for a standard hydrogen electrode ? (2) Infinite dilution, each ion makes definite (1) The hydrogen ion concentration is 1 M. contribution to equivalent conductance of an (2) Temperature is 25°C. electrolyte whatever be the nature of the other ion of the electrolyte. (3) Pressure of hydrogen is 1 bar. (3) Finite dilution, each ion makes definite (4) It contains a metallic conductor which does not contribution to equivalent conductance of an adsorb hydrogen. electrolyte whatever be the nature of the other ion of the electrolyte. EC0027 E  ® 146 Pre-Medical : Chemistry ALLEN 24. E° for the half cell ELECTROCHEMICAL SERIES Zn2+ | Zn is –0.76 V. E.M.F. of the cell 30. Zn can not displace following ions from their aqueous Zn | Zn2+ (1M) || 2H+ (1M) | H2 (1 atm) is : solution :- (1) Ag+ (2) Cu2+ (1) –0.76 V (2) +0.76 V (3) Fe 2+ (4) Na+ (3) –0.38 V (4) + 0.38 V EC0035 EC0028 31. The standard reduction potentials at 25 °C for the following half reactions are given against each :- 25. Cu(s)|Cu+2 (1 M)||Zn+2 (1 M)|Zn(s) Zn2+ (aq) + 2e– l Zn(s), –0.762 V A cell represented above should have emf. Cr3+ (aq) + 3e– l Cr(s), –0.740 V (1) Positive 2H+ + 2e– l H2(g), 0.00 V (2) Negative Fe3+ + 2e– l Fe2+, 0.77 V (3) Zero Which is the strongest reducing agent ? (4) Cannot be predicted (1) Zn (2) Cr EC0030 (3) H2(g) (4) Fe2+ (aq) 26. Given electrode potentials : EC0036 Fe3+ + e ¾® Fe2+ ; E° = 0.771 V 32. Using the standard electrode potential values given I2 + 2e ¾® 2I– ; E° = 0.536 V below, decide which of the statements, I, II, III and E°cell for the cell reaction IV are correct. Choose the right answer from (1), 2Fe3+ + 2I– ® 2Fe2+ + I2 is - (2), (3) and (4). (1) (2 × 0.771 – 0.536) = 1.006 V Fe2+ + 2e– l Fe ; E° = –0.44 V (2) (0.771 – 0.5 × 0.536) = 0.503 V Cu2+ + 2e– l Cu ; E° = +0.34 V (3) 0.771 – 0.536 = 0.235 V 21 (4) 0.536 – 0.771 = –0.235 V Ag+ + e– l Ag ; E° = +0.80 V 0- EC0031 I. Copper can displace iron from FeSO4 solution. 27. Which of the following is not an anodic reaction :– 02 II. Iron can displace copper from CuSO4 solution. (1) Ag+ ® Ag – e– :2 III. Silver can displace copper from CuSO 4 solution. (2) Cu ® Cu2+ + 2e– IV. Iron can displace silver from AgNO 3 solution. n (3) Fe2+ ® Fe3+ + e– io (1) I and II (2) II and III (4) 4OH– ® 2H2O + O2 + 4e– ss (3) II and IV (4) I and IV Se EC0032 EC0041 28. Which of the following statements is correct :– 33. The standard electrode potentials for the elements (1) Oxidation occurs at anode in both galvanic and electrolytic cell. A, B and C are 0.68, –2.50 and 0.50 V Z:\NODE02\B0B0-BA\TARGET\CHEM\ENG\MODULE-4\4.ELECTROCHEMISTRY\02-EXE.P65 (2) Reduction occurs at anode in both galvanic and respectively. The order of their reducing power is : electrolytic cell (1) A > B > C (2) A > C > B (3) Reduction occurs at anode in electrolytic cell (3) C > B > A (4) B > C > A where as oxidation occurs at cathode in galvanic cell EC0042 (4) Oxidation occurs at anode in electrolytic cell where 34. The oxidation potential of Zn, Cu, Ag, H2 and Ni as reduction occurs at anode in a galvanic cell, electrodes are 0.76 V, –0.34 V, –0.80 V, 0 V, 0.55 EC0033 V respectively. Which of the following reaction will 29. Other things being equal, the life of a Daniell cell provide maximum voltage ? may be increased by :– (1) Zn + Cu2+ ¾® Cu + Zn2+ (1) Keeping low temperature (2) Zn + 2Ag+ ¾® 2Ag + Zn2+ (2) Using large copper electrode (3) H2 + Cu2+ ¾® 2H+ + Cu (3) Decreasing concentration of copper ions (4) H2 + Ni2+ ¾® 2H+ + Ni (4) Using large zinc electrodes EC0034 EC0043 E  ® ALLEN Pre-Medical : Chemistry 147 35. The standard reduction potential at 25 °C of NERNST EQUATION Li+ / Li, Ba2+ / Ba, Na+ / Na and Mg2+ / Mg are –3.05 V, –2.73 V, –2.71 V and –2.37 V 42. E°(Ni2+/Ni) = –0.25 V respectively. Which one of the following is the E° (Au3+ / Au) = 1.50 V strongest oxidising agent ? The emf of the voltaic cell. (1) Na+ (2) Li+ (3) Ba2+ (4) Mg2+ Ni | Ni2+ (1.0 M)||Au3+ (1.0 M) | Au is : EC0045 (1) 1.25 V (2) –1.75 V 36. A gas X at 1 atm is bubbled through a solution containing a mixtu re o f 1 M Y – an d (3) 1.75 V (4) 4.0 V 1 M Z– at 25 °C. If the reduction potential of EC0052 Z > Y > X then : 43. The emf of the cell (1) Y will oxidise X and not Z (2) Y will oxidise Z and not X Tl(s)|Tl + (0.0001 M)|| Cu 2+ (0.01M)|Cu(s) (3) Y will oxidise both X and Z is 0.83 V (4) Y will reduce both X and Z The emf of this cell will be increased by :– EC0046 37. The standard electrode potential of Zn, Ag and Cu (1) Increasing the concentration of Cu+2 ions electrodes are –0.76 V, 0.80 V and 0.34 V (2) Decreasing the concentration of Tl+ respectively, then : (3) Increasing the concentration of both (1) Ag can oxidise Zn and Cu (2) Ag can reduce Zn2+ and Cu2+ (4) (1) & (2) both (3) Zn can reduce Ag+ and Cu2+ EC0054 (4) Cu can oxidise Zn and Ag 44. Which of the following represents the electrode EC0047 potential of silver electrode dipped into 0.1 M 21 38. Standard reduction potentials of four metal electrodes AgNO3 solution at 25° C ? are 0- A = – 0.250 V , B = – 0.140 V (1) E°red (2) (E°red + 0.059) 02 C = – 0.126 V , D = – 0.402 V (3) (E°ox – 0.059) (4) (E°red – 0.059) :2 The metal that displaces A from aqueous solution EC0056 of its compounds is :- 45. The electrode potential of a hydrogen electrode n (1) B (2) C dipped in solution of pH = 1 is io (3) D (4) None of the above (1) 0.059 V (2) 0.00 V ss EC0049 (3) –0.059 V (4) 0.59 V Se 39. The following four colourless salt solutions are placed EC0057 in separate test tubes and a strip of Cu is placed in each solution. Which solution finally turns blue :– 46. Consider the reaction (1) Zn(NO3)2 (2) Mg(NO3)2 Cl2(g) + 2Br–(aq) ¾® 2Cl– (aq) + Br2(l) Z:\NODE02\B0B0-BA\TARGET\CHEM\ENG\MODULE-4\4.ELECTROCHEMISTRY\02-EXE.P65 (3) KNO3 (4) AgNO3 The emf of the cell when EC0050 [Cl–] = [Br–] = 0.01 M and Cl2 gas at 0.25 atm pressure 40. Which of the following displacement does not occur will be (E° for the above reaction is = 0.29 V) (1) Zn + 2H+ ® Zn2+ + H2 ­ (1) 0.54 V (2) 0.272 V (2) Fe + 2Ag+ ® Fe2+ + Ag ¯ (3) 0.29 V (4) –0.29 V (3) Cu + Fe2+ ® Cu2+ + Fe ¯ EC0058 (4) Zn + Pb2+ ® Zn2+ + Pb ¯ 47. The standard emf for the cell reaction EC0051 Zn + Cu2+ ¾® Zn2+ + Cu is 1.10 V at 25 °C. 41. On the basis of the following E° values, the strongest The emf for the cell reaction when oxidizing agent is :- [Fe(CN)6]4– ® [Fe(CN)6]3– +e–1,E° = – 0.35 V 0.1 M Cu2+ and 0.1 M Zn2+ solution are used at Fe2+ ® Fe3+ + e–1 ; E° = – 0.77 V 25 °C is : (1) 1.10 V (2) 0.110 V (1) Fe3+ (2) [Fe(CN)6]3– (3) –1.10 V (4) –0.110 V (3) [Fe(CN)6]4– (4) Fe2+ EC0059 EC0098 E  ® 148 Pre-Medical : Chemistry ALLEN 48. E° for F2 + 2e– ® 2F– is 2.8 V, 56. What is the potential of the cell containing two E° for ½F2 + e– ® F– is ? hydrogen electrodes as represented below (1) 2.8 V (2) 1.4 V (3) –2.8 V (4) –1.4 V EC0060 Pt; H2(g) | H+(10–8)M || H+(0.001 M) | H2(g).Pt ; 49. How much will the potential of Zn | Zn change if 2+ (1) – 0.295 V (2) – 0.0591 V the solution of Zn2+ is diluted 10 times (3) 0.295 V (4) 0.0591 V (1) increases by 0.03 V (2) decreases by 0.03 V EC0070 (3) increases by 0.059 V 57. Consider the cell Cu|Cu +2 || + Ag |Ag. If the (4) decreases by 0.059 V EC0062 concentration of Cu+2 and Ag+ ions becomes ten 50. How much will the potential of a hydrogen electrode times, then the emf of the cell will :– change when its solution initially at pH = 0 is (1) Becomes 10 times neutralised to pH = 7 ? (2) Remains same (1) increases by 0.059 V (2) decreases by 0.059 V (3) Increases by 0.0295 V (3) increases by 0.41 V (4) Decreases by 0.0295 V (4) decreases by 0.41 V EC0071 EC0063 58. The emf of the cell 51. Which of the following will increase the voltage of the cell with following cell reaction Ni|Ni+2 (1.0 M) | | Au+3 (0.1M)|Au Sn(s) + 2Ag+(aq) ® Sn+2(aq) + 2Ag(s) [E° for Ni+2|Ni = –0.25 V, E° for Au+3|Au = 1.50 V] (1) Increase in the size of silver rod is given as:- (2) Increase in the concentration of Sn+2 ions (1) 1.25 V (2) – 1.75 V (3) Increase in the concentration of Ag+ ions (3) 1.78 V (4) 1.73 V 21 (4) Decrease in the concentration of Ag+ ions EC0064 EC0072 0- 52. E° for the reaction Fe + Zn2+ ® Zn + Fe2+ is 02 59. The equilibrium constant (in approx) of the cell –0.35 V. The given cell reaction is : :2 reaction : (1) spontaneous (2) non-spontaneous Cu(s) + 2Ag+(aq.) ƒ Cu+2(aq.) + 2Ag(s) n (3) in equilibrium (4) can't say anything if E°cell = 0.465 V at 298 K is :- io EC0065 (1) 2.0 × 1010 (2) 3.16 × 1012 ss 53. For a reaction - A(s) + 2B+ ƒ A2+ + 2B(s) (3) 3.16 × 1015 (4) 4 × 1010 Se KC has been found to be 1012. The E°cell is: EC0097 (1) 0.354 V (2) 0.708 V (3) 0.0098 V (4) 1.36 V 60. The emf of the cell in which the following reaction Z:\NODE02\B0B0-BA\TARGET\CHEM\ENG\MODULE-4\4.ELECTROCHEMISTRY\02-EXE.P65 EC0066 Zn(s) + Ni2+ (a = 0.1) ƒ Zn2+ (a = 1.0) + Ni(s) 54. The standard electrode potential (E°) for OCl–/Cl– occurs, is found to be 0.5105 V at 298 K. The and Cl / ½ Cl 2 respectively are 0.94 V and – standard e.m.f. of the cell is :- –1.36 V. The E° value of OCl– / ½ Cl2 will be : (1) –0.5105 V (2) 0.5400 V (1) –2.20 V (2) –0.42 V (3) 0.4810 V (4) 0.5696 V (3) 0.52 V (4) 1.04 V EC0053 EC0067 61. If E oFe+2 / Fe = – 0.441V and E oFe+3 /Fe+2 = 0.771V the 55. The hydrogen electrode is dipped in a solution of pH = 3 at 25 °C. The electrode potential of the half standard EMF of the reaction Fe + 2Fe +3 ® 3Fe+2 cell would be : will be : (1) 0.177 V (2) – 0.177 V (1) 0.330 V (2) 1.653 V (3) 0.087 V (4) 0.059 V (3) 1.212 V (4) 0.111 V EC0093 EC0069 E  ® ALLEN Pre-Medical : Chemistry 149 69. A silver cup is plated with silver by passing ELECTROLYSIS 965 A current for one second, the mass of Ag 62. When an electric current is passed through acidified deposited is :–(At. wt. of Ag = 107.87) water, 112 mL of hydrogen gas at STP collects at (1) 9.89 g. (2) 107.87 g. the cathode in 965 s. The current passed in ampere (3) 1.0787 g. (4) 100.2 g. is : EC0082 (1) 1.0 (2) 0.5 70. When electricity is passed through a solution of (3) 0.1 (4) 2.0 AlCl3, 13.5 g Al is deposited. The number of EC0073 Faradays must be :– (1) 5.0 (2) 1.0 (3) 1.5 (4) 3.0 63. Two electrolytic cells one containing acidified ferrous chloride and another acidified ferric chloride are EC0083 connected in series. The ratio of iron deposited at 71. A solution of sodium sulphate in water is electrolysed using inert electrodes. The product at the cathode cathodes in the two cells when electricity is passed and anode are respectively :– through the cells will be : (1) H2, SO2 (2) O2, H2 (1) 3 :1 (2) 2 : 1 (3) 1 : 1 (4) 3 : 2 (3) O2, Na (4) H2, O2 EC0074 EC0084 72. One Faraday of electricity will liberate one mole of 64. A current of 9.65 A flowing for 10 minute deposits the metal from the solution of 3.0 g of a metal. The equivalent weight of the metal (1) Auric chloride (AuCl3) (2) Silver nitrate is : (3) Calcium chloride (4) Copper sulphate (1) 10 (2) 30 (3) 50 (4) 96.5 EC0085 73. When 96500 C of electricity are passed through EC0075 21 barium chloride solution, the amount of barium deposited will be :- 0- 65. How many coulombs of electric charge are required (1) 0.5 mol (2) 1.0 mol 02 for the oxidation of 1 mol of H2O to O2 ? (3) 1.5 mol (4) 2.0 mol (1) 9.65 × 104 C (2) 4.825 × 105 C :2 EC0086 (3) 1.93 × 105 C (4) 1.93 × 104 C 74. A factory produces 40 kg of calcium in two hours by n EC0077 electrolysis. How much aluminium can be produced io by the same current in two hours :– 66. On passing 10800 C through electrolytic solution, ss (1) 22 kg (2) 18 kg 2.977 g of metal (atomic mass 106.4 g mol–1) was (3) 9 kg (4) 27 kg Se deposited, the charge on the metal cation is - EC0087 (1) +4 (2) +3 (3) +2 (4) +1 75. What would be the ratio of moles of Ag, Cu, Fe that would be deposited by passage of same quantity of Z:\NODE02\B0B0-BA\TARGET\CHEM\ENG\MODULE-4\4.ELECTROCHEMISTRY\02-EXE.P65 EC0079 electricity through solutions of salts containing Ag+, 67. On passing electricity through dilute H2SO4 solution Cu+2, Fe+3 :- the amount of substance liberated at the cathode and anode are in the ratio : 1 1 (1) 1 : 1 : 1 (2) 1 : : (1) 1 : 8 (2) 8 : 1 2 3 (3) 16 : 1 (4) 1 : 16 1 1 EC0080 (3) : :1 (4) 1 : 2 : 3 3 2 68. During electrolysis of fused calcium hydride, the EC0088 hydrogen is produced at : 76. Electrolysis of aq. CuSO4 causes :– (1) Cathode (1) An increase in pH (2) Anode (2) A decrease in pH (3) Hydrogen is not liberated at all (3) Either decrease or increase in pH (4) H2 produced reacts with oxygen to form water (4) None EC0081 EC0089 E  ® 150 Pre-Medical : Chemistry ALLEN 77. The passage of current liberates H2 at cathode and 79. The thermodynamic efficiency of cell is given by - Cl2 at anode. The solution is :– DH nFE (1) × 100 (2) × 100 (1) CuSO4 (aq) (2) CuCl2 (aq.) DG DG (3) NaCl (aq.) (4) Water nFE EC0090 (3) – × 100 (4) Zero DH COMMERCIAL CELLS EC0169 78. When lead accumulator is charged, it acts as : (1) an electrolytic cell (2) a galvanic cell (3) a Daniel cell (4) none of the above EC0091 21 0- 02 :2 n io ss Se Z:\NODE02\B0B0-BA\TARGET\CHEM\ENG\MODULE-4\4.ELECTROCHEMISTRY\02-EXE.P65 EXERCISE-I (Conceptual Questions) ANSWER KEY Que. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Ans. 3 2 3 1 3 3 3 2 1 2 1 1 1 3 1 Que. 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Ans. 2 4 2 2 2 4 2 4 2 2 3 1 1 4 4 Que. 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Ans. 1 3 4 2 4 1 3 3 4 3 1 3 4 4 3 Que. 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Ans. 2 1 1 1 4 3 2 1 3 2 3 3 4 3 2 Que. 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 Ans. 3 1 4 3 3 1 1 2 3 3 4 2 1 2 2 Que. 76 77 78 79 Ans. 2 3 1 3 E  ® ALLEN Pre-Medical : Chemistry 151 EXERCISE-II (Previous Year Questions) AIPMT/NEET AIPMT 2009 6. Which of the following expressions correctly 1. Given : represents the equivalent conductance of Al2(SO4)3 (i) Cu2+ + 2e– ® Cu, E° = 0.337 V (ii) Cu2+ + e– ® Cu+, E° = 0.153 V at infinite dilution. Given that L° Al3+ and L°SO2– 4 are Electrode potential, E° for the reaction, Cu+ + e– ® Cu, the equivalent conductances at infinite dilution of the will be :- respective ions :- (1) 0.38 V (2) 0.52 V (3) 0.90 V (4) 0.30 V EC0100 (1) L° Al3 + + L° SO2– 4 ( ) (2) L° Al3 + + L°SO 2– ´ 6 4 M 2. The equivalent conductance of solution of a 1 0 1 32 (3) Ù Al3 + + Ù0SO2 - (4) 2L°Al3 + + 3L°SO2– weak monobasic acid is 8.0 mho cm2 eq–1and at 3 2 4 4 infinite dilution is 400 mho cm2 eq–1. The dissociation constant of this acid is :- EC0105 (1) 1.25 × 10–4 (2) 1.25 × 10–5 –6 7. For the reduction of silver ions with copper metals, (3) 1.25 × 10 (4) 6.25 × 10–4 the standard cell potential was found to be +0.46 V EC0101 at 25 °C. The value of standard Gibbs energy. DG° 3. Al2O3 is reduced by electrolysis at low potential and will be (F = 96500 C mol–1) high current. If 4.0 × 104 A of current is passed through molten Al2O3 for 6 hours, what mass of (1) –98.0 kJ (2) –89.0 kJ aluminium is produced ? (Assume 100% current (3) –89.0 J (4) –44.5 kJ efficiency, At. mass of Al = 27 g mol–1) (1) 1.3 × 104 g (2) 9.0 × 103 g EC0106 4 (3) 8.1 × 10 g (4) 2.4 × 105 g 21 AIPMT Pre. 2011 EC0102 8. Standard electrode potential of three metals X, Y 0- AIPMT 2010 and Z are –1.2 V, +0.5 V and –3.0 V respectively. 02 4. An increase in equivalent conductance of a strong The reducing power of these metals will be :- electrolyte with dilution is mainly due to:- :2 (1) Y > Z > X (2) Y > X > Z (1) Increase in number of ions. (3) Z > X > Y (4) X > Y > Z n (2) Increase in ionic mobility of ions. EC0109 io (3) 100% ionisation of electrolyte at normal dilution. ss 9. The electrode potentials for (4) Increase in both i.e. number of ions and ionic 2+ – + Se Cu (aq) + e ® Cu (aq) mobility of ions. + – and Cu (aq) + e ® Cu(s) EC0103 are +0.15 V and +0.50 V respectively. The value Z:\NODE02\B0B0-BA\TARGET\CHEM\ENG\MODULE-4\4.ELECTROCHEMISTRY\02-EXE.P65 5. Consider the following relations for emf of a electrochemical cell : of E°Cu2+ / Cu will be :- (a) emf of cell =(Oxidation potential of anode) – (1) 0.500 V (2) 0.325 V (Reduction potential of cathode) (3) 0.650 V (4) 0.150 V (b) emf of cell = (Oxidation potential of anode) + EC0110 (Reduction potential of cathode) 10. Standard electrode potential for Sn4+/Sn2+ couple (c) emf of cell = (Reduction potential of anode) is +0.15 V and that for the Cr3+/Cr couples is + (Reduction potential of cathode) –0.74 V. These two couples in their standard state (d) emf of cell = (Oxidation potential of anode) – are connected to make a cell. The standard cell (Oxidation potential of cathode) potential will be :- Which of the above relations are correct : (1) +1.19 V (2) +0.89 V (1) (a) and (b) (2) (c) and (d) (3) +0.18 V (4) +1.83 V (3) (b) and (d) (4) (c) and (a) EC0111 EC0104 E  ® 152 Pre-Medical : Chemistry ALLEN 11. If the E°cell for a given reaction has a negative value, NEET-UG 2013 then which of the following gives the correct 15. At 25 °C molar conductance of 0.1 molar aqueous relationship for the values of DG° and Keq ? solution of ammonium hydroxide is 9.54 ohm–1 cm2 (1) DG° > 0; Keq > 1 (2) DG° < 0; Keq > 1 mol–1 and at infinite dilution its molar conductance is 238 ohm–1 cm2 mol–1. The degree of ionisation (3) DG° < 0; Keq < 1 (4) DG° > 0; Keq < 1 of ammonium hydroxide at the same concentration EC0112 and temperature is :- (1) 40.800 % (2) 2.080 % AIPMT Mains 2011 (3) 20.800 % (4) 4.008 % 12. A solution contains Fe 2+ , Fe 3+ and I – ions. EC0117 This solution was treated with iodine at 35 °C. E° f or Fe 3+ | Fe 2+ is +0.77 V and E° for 16. A hydrogen gas electrode is made by dipping I 2 |2I – = 0.536 V. The f avourable redox platinum wire in a solution of HCl of pH = 10 and reaction is :- by passing hydrogen gas around the platinum wire at 1 atm pressure. The oxidation potential of (1) Fe2+ will be oxidised to Fe3+ electrode would be ? (2) I2 will be reduced to I– (1) 1.18 V (2) 0.059 V (3) There will be no redox reaction (3) 0.59 V (4) 0.118 V (4) I– will be oxidised to I2 EC0118 EC0113 17. A button cell used in watches function as following Zn(s)+Ag2O(s)+H2O(l) ƒ 2Ag(s)+Zn2+(aq)+2OH–(aq) AIPMT Pre. 2012 21 If half cell potentials are 13. Limiting molar conductivity of NH4OH Zn2+(aq) + 2e– ® Zn(s); E° = –0.76 V 0- ( i.e.L ( ) is equal to:- Ag2O(s) + H2O(l) + 2e– ® 2Ag(s) + 2OH–(aq); 02 ° m NH4 OH ) E° = 0.34 V :2 The standard cell potential will be :- ° ° ° n (1) L m (NH4OH ) + L m (NH4Cl ) - L m (HCl ) (1) 1.34 V (2) 1.10 V io (3) 0.42 V (4) 0.84 V ss ° ° ° EC0119 (2) L m (NH4Cl ) + L m (NaOH ) - L m (NaCl ) Se AIPMT 2014 ° ° ° (3) L m (NH4Cl ) + L m (NaCl ) - L m (NaOH ) 18. When 0.1 mol MnO 24 - is oxidised the quantity of Z:\NODE02\B0B0-BA\TARGET\CHEM\ENG\MODULE-4\4.ELECTROCHEMISTRY\02-EXE.P65 electricity required to completely oxidise MnO 24 - ° ° ° (4) Lm(NaOH) + Lm(NaCl) - Lm (NH4Cl ) to MnO-4 is :- EC0114 (1) 96500 C (2) 2 × 96500 C (3) 9650 C (4) 96.50 C AIPMT Mains 2012 14. Molar conductivities ( L om ) at infinite dilution of NaCl, EC0121 HCl and CH 3COONa are 126.4, 425.9 and 19. The weight of silver (at wt. = 108) displaced by a quantity of electricity which displaces 5600 mL of 91.0 S cm2 mol–1 respectively. L om for CH3COOH O2 at STP will be :- will be :- (1) 5.4 g (2) 10.8 g (1) 290.8 S cm2 mol–1 (2) 390.5 S cm2 mol–1 (3) 425.5 S cm2 mol–1 (4) 180.5 S cm2 mol–1 (3) 54.0 g (4) 108.0 g EC0115 EC0122 E  ® ALLEN Pre-Medical : Chemistry 153 AIPMT 2015 NEET(UG) 2017 20. A device that converts energy of combustion of fuels 26. In the electrochemical cell :- like hydrogen and methane, directly into electrical energy is known as :- Zn|ZnSO4(0.01M)||CuSO4(1.0 M)|Cu, the emf of this Daniel cell is E1. When the concentration of (1) Electrolytic cell (2) Dynamo ZnSO4 is changed to 1.0M and that of CuSO4 (3) Ni-Cd cell (4) Fuel Cell changed to 0.01M, the emf changes to E2. Which one of the relationship is correct between E1 EC0124 and E2? NEET-I 2016 RT (Given, = 0.059 ) 21. The pressure of H2 required to make the potential F of H2-electrode zero in pure water at 298 K is :- (1) E1 < E2 (2) E1 > E2 (1) 10–14 atm (2) 10–12 atm (3) E2 = 0 ¹ E1 (4) E1 = E2 (3) 10–10 atm (4) 10–4 atm EC0133 EC0127 NEET(UG) 2018 27. Consider the change in oxidation state of Bromine NEET-II 2016 corresponding to different EMF values as shown in 22. The molar conductivity of a 0.5 mol/dm 3 the diagram below: solution of AgNO3 with electrolytic conductivity of 1.82 V 1.5 V BrO4 BrO3 HBrO 5.76 × 10–3 S cm–1 at 298 K is (1) 0.086 S cm2/mol (2) 28.8 S cm2/mol Br Br2 1.0652V 1.595 V 21 (3) 2.88 S cm2/mol (4) 11.52 S cm2/mol Then the species undergoing disproportionation is:- 0- (1) BrO3– (2) BrO4– 02 EC0128 (3) Br2 (4) HBrO :2 23. During the electrolysis of molten sodium chloride, EC0135 the time required to produce 0.10 mol of chlorine NEET(UG) 2019 n gas using a current of 3 A is io 28. For a cell involving one electron E°cell = 0.59V at ss (1) 220 minutes (2) 330 minutes 298 K, the equilibrium constant for the cell reaction Se (3) 55 minutes (4) 110 minutes is :- EC0129 é 2.303RT ù êë Given that = 0.059V at T = 298K ú Z:\NODE02\B0B0-BA\TARGET\CHEM\ENG\MODULE-4\4.ELECTROCHEMISTRY\02-EXE.P65 F û 24. If the E°cell for a given reaction has a negative value, which of the following gives the correct relationships (1) 1.0 × 102 (2) 1.0 × 105 for the values of DG° and Keq ? (3) 1.0 × 1010 (4) 1.0 × 1030 (1) DG° < 0; Keq > 1 (2) DG° < 0; Keq < 1 EC0192 29. For the cell reaction (3) DG° > 0; Keq < 1 (4) DG° > 0; Keq > 1 2Fe3+ (aq) + 2I–(aq) ® 2Fe2+(aq) + I2(aq) EC0130 E ocell = 0.24V at 298 K. The standard Gibbs energy 25. The number of electrons delivered at the cathode during electrolysis by a current of 1 A in 60 s is (charge on electron = 1.60 × 10–19 C) (D G ) r o of the cell reaction is : (1) 3.75 × 1020 (2) 7.48 × 1023 [Given that Faraday constant F = 96500 C mol–1] (1) – 46.32 kJ mol–1 (2) – 23.16 kJ mol–1 (3) 6 × 1023 (4) 6 × 1020 (3) 46.32 kJ mol–1 (4) 23.16 kJ mol–1 EC0131 EC0193 E  ® 154 Pre-Medical : Chemistry ALLEN 31. The standard electrode potential (E°) values of NEET(UG) (Odisha) 2019 Al 3+ |Al, Ag + |Ag, K + |K and Cr 3+ |Cr are 30. Following limiting molar conductivities are given as –1.66 V, 0.80V, –2.93 V and –0.74 V respectively. l0m (H2 SO4 ) = x S cm2 mol -1 The correct decreasing order of reducing power of the metal is : l0m (K2SO4 ) = y S cm2 mol -1 (1) Ag > Cr > Al > K (2) K > Al > Cr > Ag l0m( CH3COOK ) = z S cm2 mol -1 (3) K > Al > Ag > Cr (4) Al > K > Ag > Cr EC0195 l0m (in S cm2 mol–1) for CH3COOH will be- (1) x – y + 2 z (2) x + y – z (x - y) + z (3) x – y + z (4) 2 EC0194 21 0- 02 :2 n io ss Se Z:\NODE02\B0B0-BA\TAR