Electrochemistry

A device that converts energy of combustion of fuels like hydrogen and methane, directly into electrical energy is known as

1. dynamo
2. Ni-Cd cell
3. fuel cell
4. electrolytic cell

When 0.1 mol MnO42- is oxidised the quantity of electricity required to completely oxidise MnO42- to MnO4- is

1. 96500 C
2. 2 96500 C
3. 9650 C
4. 96.50 C

The weight of silver (at. wt. = 108) displaced by a quantity of electricity which displaces 5600 mL of O2 at STP will be

1. 5.4 g
2. 10.8 g
3. 54.0 g
4. 108.0 g

At 25 C molar conductance of 0.1 molar aqueous solution of ammonium hydroxide is 9.54 ohm-1 cm2 mol-1 and at infinite dilution its molar conductance is 238 ohm-1 cm2 mol-1. The degree of ionisation of ammonium hydroxide at the same concentration and temperature is

1. 4.008\%
2. 40.800\%
3. 2.080\%
4. 20.800\%

A button cell used in watches functions as follows. Zn(s) + Ag2O(s) + H2O(l) 2Ag(s) + Zn2+(aq) + 2OH-(aq) If half cell potentials are Zn2+(aq) + 2e- Zn(s); E = -0.76 V Ag2O(s) + H2O(l) + 2e- 2Ag(s) + 2OH-(aq), E = 0.34 V The cell potential will be

1. 0.84 V
2. 1.34 V
3. 1.10 V
4. 0.42 V

A hydrogen gas electrode is made by dipping platinum wire in a solution of pH = 10 and by passing hydrogen gas around the platinum wire at one atm pressure. The oxidation potential of electrode would be

1. 0.118 V
2. 1.18 V
3. 0.059 V
4. 0.59 V

Consider the half-cell reduction reaction Mn2+ + 2e- Mn, E = -1.18 V Mn2+ Mn3+ + e-, E = -1.51 V The E for the reaction 3Mn2+ Mn + 2Mn3+, and possibility of the forward reaction are respectively

1. -4.18 V and yes
2. +0.33 V and yes
3. +2.69 V and no
4. -2.69 V and no

How many gram 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)

1. 4.0
2. 20.0
3. 40.0
4. 0.66

Standard reduction potentials of the half reactions are given below : F2(g) + 2e- 2F-(aq); E = +2.85 V Cl2(g) + 2e- 2Cl-(aq); E = +1.36 V Br2(l) + 2e- 2Br-(aq); E = +1.06 V I2(s) + 2e- 2I-(aq); E = +0.53 V The strongest oxidising and reducing agents respectively are

1. F2 and I-
2. Br2 and Cl-
3. Cl2 and Br-
4. Cl2 and I2

Molar conductivities ( m) at infinite dilution of NaCl, HCl and CH3COONa are 126.4, 425.9 and 91.0 S cm2 mol-1 respectively. ( m) for CH3COOH will be

1. 425.5 S cm2 mol-1
2. 180.5 S cm2 mol-1
3. 290.8 S cm2 mol-1
4. 390.5 S cm2 mol-1

Limiting molar conductivity of NH4OH [i.e. 0m(NH4OH)] is equal to

1. 0m(NH4OH) + 0m(NaCl) - 0m(NaOH)
2. 0m(NaOH) + 0m(NaCl) - 0m(NH4Cl)
3. 0m(NH4OH) + 0m(NH4Cl) - 0m(HCl)
4. 0m(NH4Cl) + 0m(NaOH) - 0m(NaCl)

A solution contains Fe2+, Fe3+ and I- ions. This solution was treated with iodine at 35 C. E for Fe3+/Fe2+ is +0.77 V and E for I2/2I- = 0.536 V. The favourable redox reaction is

1. I2 will be reduced to I-
2. there will be no redox reaction
3. I- will be oxidised to I2
4. Fe2+ will be oxidised to Fe3+

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

1. Y > Z > X
2. Y > X > Z
3. Z > X > Y
4. X > Y > Z

The electrode potentials for Cu2+(aq) + e- Cu+(aq) and Cu+(aq) + e- Cu(s) are +0.15 V and +0.50 V respectively. The value of E Cu2+/Cu will be

1. 0.500 V
2. 0.325 V
3. 0.650 V
4. 0.150 V

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

1. +1.19 V
2. +0.89 V
3. +0.18 V
4. +1.83 V

Which of the following expressions correctly represents the equivalent conductance at infinite dilution of Al2(SO4)3. Given that Al3+ and SO42- are the equivalent conductances at infinite dilution of the respective ions?

1. 2 Al3+ + 3 SO42-
2. Al3+ + SO42-
3. ( Al3+ + SO42-) 6
4. 13 Al3+ + 12 SO42-

Consider the following relations for emf of an electrochemical cell (i) EMF of cell = (Oxidation potential of anode) − (Reduction potential of cathode) (ii) EMF of cell = (Oxidation potential of anode) + (Reduction potential of cathode) (iii) EMF of cell = (Reduction potential of anode) + (Reduction potential of cathode) (iv) EMF of cell = (Oxidation potential of anode) − (Oxidation potential of cathode) Which of the above relations are correct?

1. (iii) and (i)
2. (i) and (ii)
3. (iii) and (iv)
4. (ii) and (iv)

For the reduction of silver ions with copper metal, the standard cell potential was found to be +0.46 V at 25 C. The value of standard Gibbs energy, G will be (F = 96500 C mol-1)

1. -89.0 kJ
2. -89.0 J
3. -44.5 kJ
4. -98.0 kJ

An increase in equivalent conductance of a strong electrolyte with dilution is mainly due to

1. increase in ionic mobility of ions
2. 100% ionisation of electrolyte at normal dilution
3. increase in both i.e., number of ions and ionic mobility of ions
4. increase in number of ions.

Given : (i) Cu2+ + 2e- Cu, E = 0.337 V (ii) Cu2+ + e- Cu+, E = 0.153 V Electrode potential, E for the reaction, Cu+ + e- Cu, will be

1. 0.90 V
2. 0.30 V
3. 0.38 V
4. 0.52 V

Al2O3 is reduced by electrolysis at low potentials and high currents. If 4.0 104 amperes of current is passed through molten Al2O3 for 6 hours, what mass of aluminium is produced? (Assume 100% current efficiency, at. mass of Al = 27 g mol-1).

1. 8.1 104 g
2. 2.4 105 g
3. 1.3 104 g
4. 9.0 103 g

The equivalent conductance of M/32 solution of a weak monobasic acid is 8.0 mho cm2 and at infinite dilution is 400 mho cm2. The dissociation constant of this acid is

1. 1.25 10-6
2. 6.25 10-4
3. 1.25 10-4
4. 1.25 10-5

On the basis of the following E values, the strongest oxidizing agent is [Fe(CN)6]4- [Fe(CN)6]3- + e-; E = -0.35 V Fe2+ Fe3+ + e-; E = -0.77 V

1. Fe3+
2. [Fe(CN)6]3-
3. [Fe(CN)6]4-
4. Fe2+

Kohlrausch's law states that at

1. Infinite dilution, each ion makes definite contribution to conductance of an electrolyte whatever be the nature of the other ion of the electrolyte
2. Infinite dilution, each ion makes definite contribution to equivalent conductance of an electrolyte, whatever be the nature of the other ion of the electrolyte
3. Finite dilution, each ion makes definite contribution to equivalent conductance of an electrolyte, whatever be the nature of the other ion of the electrolyte
4. Infinite dilution, each ion makes definite contribution to equivalent conductance of an electrolyte depending on the nature of the other ion of the electrolyte.

Standard free energies of formation (in kJ/mol) at 298 K are -237.2, -394.4 and -8.2 for H2O(l), CO2(g) and pentane (g) respectively. The value of E cell for the pentane-oxygen fuel cell is

1. 1.0968 V
2. 0.0968 V
3. 1.968 V
4. 2.0968 V

The equilibrium constant of the reaction: Cu(s) + 2Ag+(aq) Cu2+(aq) + 2Ag(s); E = 0.46 V at 298 K is

1. 2.0 1010
2. 4.0 1010
3. 4.0 1015
4. 2.4 1010

The efficiency of a fuel cell is given by

1. G/ S
2. G/ H
3. S/ G
4. H/ G

A hypothetical electrochemical cell is shown below. A | A+(xM) || B+(yM) | B The emf measured is + 0.20 V. The cell reaction is

1. A + B+ A+ + B
2. A+ + B A + B+
3. A+ + e- A; B+ + e- B
4. the cell reaction cannot be predicted.

E Fe2+/Fe = -0.441 V and E Fe3+/Fe2+ = 0.771 V, the standard EMF of the reaction Fe + 2Fe3+ 3Fe2+ will be

1. 0.111 V
2. 0.330 V
3. 1.653 V
4. 1.212 V

4.5 g of aluminium (at. mass 27 amu) is deposited at cathode from Al3+ 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

1. 44.8 L
2. 22.4 L
3. 11.2 L
4. 5.6 L