Electrochemistry · Question 32

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+