CHAPTER ELECTROCHEMISTRY

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149 CHAPTER ELECTROCHEMISTRY 1. On electrolysis of dilute sulphuric acid using platinum electrodes, the product obtained at the anode will be hydrogen oxygen hydrogen sulphide sulphur dioxide 2.

1 149 CHAPTER ELECTROCHEMISTRY 1. On electrolysis of dilute sulphuric acid using platinum electrodes, the product obtained at the anode will be hydrogen oxygen hydrogen sulphide sulphur dioxide 2. Which of the following is an insulator? Graphite Aluminium Diamond Silicon 3. Na+ Li+ Ba 2+ Mg The most durable metal plating on iron to protect against corrosion is nickel plating copper plating tin plating zinc plating 5. On heating one end of a piece of a metal, the other end becomes hot because of resistance of the metal mobility of atoms in the metal energised electrons moving to the other end minor perturbation in the energy of atoms 6. If 0.5 amp current is passed through acidified silver nitrate solution for 100 minutes. The mass of silver deposited on cathode, is (eq.wt.of silver nitrate = 108) g g g g 7. the temperature is constant e.m.f depends on molarities of acids used acids used in two compartments are different phof 0.1 MHCl and 0.1 MCH3COOH is not same 8. On passing a current of 1.0 ampere for 16 min and 5 sec through one litre solution of CuCl 2, all copper of the solution was deposited at cathode. The strength of CuCl2 solution was (Molar mass of Cu= 63.5; Faraday constant = 96,500 Cmol 1 ) 0.01 N 0.01 M 0.02 M 0.2 N Ans: 9. Equivalent conductances of NaCl, HCl and CH3COONa at infinite dilution are , and 91 ohm 1 cm2 respectively. The equivalent conductance of CH3COOH at infinite dilution would be ohm 1 cm ohm 1 cm ohm 1 cm ohm 1 cm If 0.01 Msolution 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

2 V V V V 16. The ionic conductance of Ba 2+ and Cl are respectively 127 and 76 ohm 1 cm 2 at infinite dilution. The equivalent conductance (in ohm 1 cm 2 ) of BaCl2 at infinite dilution will be: Ans: ln (C1) ln (C2 /C1) ln (C2) ln (C1 + C2) 14. Without losing its concentration ZnCl2 solution cannot be kept in contact with Au Al Pb Ag V V V 0.19 V 18. Specific conductance of a 0.1 NKCl solution at 23ºC is ohm 1 cm 1. Resistance of cell containing the solution at same temperature was found to be 55 ohm. The cell constant is cm cm cm cm 1 19.

151 20. The most convenient method to protect the bottom of ship made of iron is Coating it with red lead oxide White tin plating Connecting it with Mg block Connecting it with Pb block 21.

3 The most convenient method to protect the bottom of ship made of iron is Coating it with red lead oxide White tin plating Connecting it with Mg block Connecting it with Pb block 21. In the silver plating of copper, K[Ag(CN) 2] is used instead of AgNO3. The reason is Athin layer of Ag is formed on Cu More voltage is required Ag + ions are completely removed from solution Less availability of Ag + ions, as Cu cannot displace Ag from [Ag(CN) 2] ion V 2.14 V 4.28 V 6.42 V Which reaction is not feasible? 23. In electrolysis of NaCl when Pt electrode is taken then H2 is liberated at cathode while with Hg cathode it forms sodium amalgam. This is because Hg is more inert than Pt More voltage is required to reduce H + at Hg than at Pt Na is dissolved in Hg while it does not dissolve in Pt Conc. of H + ions is larger when Pt electrode is taken g of aluminium (at. mass 27 amu) is deposited at cathode from Al 3+ solution by a certain quantity of electric charge. The volume of hydrogen produced at STP from H + ions in solution by the same quantity of electric charge will be 44.8 L 22.4 L 11.2 L 5.6 L V V V

152 0.330 V 29. 30. The efficiency of a fuel cell is given by electrolyte, whatever be the nature of the other ion of the electrolyte.

4 V The efficiency of a fuel cell is given by electrolyte, whatever be the nature of the other ion of the electrolyte. infinite dilution each ion makes definite contribution to equivalent conductance of an electrolyte depending on the nature of the other ion of the electrolyte. infinite dilution, each ion makes definite contribution to conductance of an electrolyte whatever be the nature of the other ion of the electrolyte. infinite dilution, each ion makes definite contirubtion to equivalent conductance of an electrolyte, whatever be the nature of the other ion of the electrolyte V V V V V 0.30 V 0.38 V 0.52 V [Fe(CN) 6] 4 Fe 2+ Fe 3+ [Fe(CN) 6] Kohlrausch s law states that at: finite dilution, each ion makes definite contribution to equivalent conductance of an g g g g Ans: 37.

153 1.25 10 6 6.25 10 4 1.25 10 4 1.25 10 5 41. 38. 89.0 kj 89.0 J 44.5 kj 98.0 kj Ans: 39.

Standard electrode potential of three metals X, Yand Zare 1.2 V, + 0.5 Vand 3.0 V, respectively. The reducing power of these metals will be: Y> Z> X X> Y> Z Z> X> Y X> Y> Z 43. 40. 0.500 V 0.

5 kj 89.0 J 44.5 kj 98.0 kj Ans: 39. increase in ionic mobility of ions 100% ionisation of electrolyte at normal dilution increase in both i.e. number of ions and ionic mobility of ions increase in number of ions Ans: (ii) and (iv) (iii) and and (ii) (iii) and (iv) Ans: 42. Standard electrode potential of three metals X, Yand Zare 1.2 V, Vand 3.0 V, respectively. The reducing power of these metals will be: Y> Z> X X> Y> Z Z> X> Y X> Y> Z V V V V 44. Standard electrode potential for Sn 4+ / Sn 2+ couple is Vand that for the Cr 3+ / Cr couple is 0.74 V. These two couples in their standard state are connected to make a cell. The cell potential will be:

154 + 1.19 V + 0.89 V + 0.18 V + 1.83 V 45. 290.8 S cm 2 mol 1 390.5 S cm 2 mol 1 49.

6 V V V V S cm 2 mol S cm 2 mol Ahydrogen gas electrode is made by dipping platinum wire in a solution of HCl of ph= 10 and by passing hydrogen gas around the platinum wire at one atm pressure. The oxidation potential of electrode would be? 0.59 V V 1.18 V V Ans: I2 will be reduced to I There will be no redox reaction I will be oxidised to I2 Fe 2+ will be oxidised to Fe % 4.008% % 2.080% S cm 2 mol S cm 2 mol V 0.84 V 1.34 V 1.10 V 52. How many grams of cobalt metal will be deposited when a solution of cobalt (II) chloride is electrolyzed with a current of 10 amperes for 109 minutes (1 Faraday = 96,500 C; Atomic mass of Co = 59 u)

155 40.0 53. 2.69 V and no 4.18 V and yes + 0.

7 V and no 4.18 V and yes V and yes V and no Ans:

Solved Examples On Electrochemistry

Solved Examples On Electrochemistry Example 1. Find the charge in coulomb on 1 g-ion of Charge on one ion of N 3- = 3 1.6 10-19 coulomb Thus, charge on one g-ion of N 3- = 3 1.6 10-19 6.02 10 23 = 2.89