1. The number of Coulombs of electricity required to deposit 0.3 mole of Cu is[MOE Model]
- 9650
- 2 × 9650
- 4 × 9650
- 6 × 9650
(d) Cu²⁺ + 2e⁻ → Cu ⇒ 0.3 mol Cu requires 0.6 F = 0.6 × 96500 C = 6 × 9650 C. 2. The amount of electricity required to deposit 0.2 mole of Ag⁺ is[MOE 2008]
- 3 × 9650
- 2 × 9650
- 2 × 96500
- 96500
(b) Ag⁺ + e⁻ → Ag ⇒ 0.2 mol Ag requires 0.2 F = 0.2 × 96500 C = 2 × 9650 C. 3. When sodium chloride is electrolysed, which reaction takes place at anode?[MOE 2060]
- Na → Na⁺ + e⁻
- Na⁺ → Na + e⁻
- 2Cl⁻ → Cl₂ + 2e⁻
- Cl₂ + 2e⁻ → 2Cl⁻
(c) Chloride ions (Cl⁻) are oxidized to chlorine gas (Cl₂) at the anode. 4. Electrochemical equivalent refers to mass deposited in which case?[MOE 2060]
- 1 Faraday
- 1 Coulomb
- 1 ampere of current for 1 minute
- 96500 Coulomb charge
(b) Electrochemical equivalent is the mass deposited by 1 Coulomb of electricity. 5. CuSO₄ is electrolyzed by passing 1 Faraday of current. At anode, there is[MOE 2003]
- Loss of 32 gram
- Gain of 32 gram
- Loss of 64 gram
- Gain of 64 gram
(a) At anode: 2H₂O → O₂ + 4H⁺ + 4e⁻. 1 F oxidizes 8g O₂ (equivalent to 32g Cu loss). 6. In electrolysis, amount of silver deposited equivalent to 112 ml of Hydrogen is[MOE 2054]
- 108 gm
- 10.8 gm
- 1.08 gm
- 0.108 gm
(c) 112 ml H₂ at STP = 0.005 mol. Equivalent Ag = 0.005 × 108 = 1.08 g (1:1 eq ratio). 7. An electric current of 0.25 Amp was passed through acidified water for 2 hours. Volume of H₂ produced at NTP?[IOM 08]
- 0.108 litre
- 0.2016 litre
- 0.36 litre
- 0.408 litre
(b) Charge = 0.25 A × 7200 s = 1800 C. Moles H₂ = 1800/(2×96500) ≈ 0.009 ⇒ Volume ≈ 0.2016 L. 8. Given: Zn²⁺ + 2e⁻ → Zn (E°=-0.76 V); Mg²⁺ + 2e⁻ → Mg (E°=-2.37 V). When Zn dust is added to MgCl₂ solution:[B.E. 2065]
- Zn is dissolved
- ZnCl₂ is formed
- Mg is crystallized out
- No reaction
(d) Zn cannot reduce Mg²⁺ (E°(Zn²⁺/Zn) > E°(Mg²⁺/Mg)) ⇒ No reaction. 9. In electrolysis of water, 224 liters of H₂ was liberated at NTP. Weight of O₂ liberated will be[MOE 2065]
(b) 224 L H₂ = 10 mol ⇒ 5 mol O₂ (2:1 ratio) ⇒ Mass = 5 × 32 = 160 g. 10. The weight of Ag deposited when 465.5 coulomb electricity is passed is[I.E. 2009]
- 0.521 g
- 0.480 g
- 0.441 g
- 0.465 g
(a) Moles Ag = 465.5/96500 ≈ 0.00482 ⇒ Mass ≈ 0.00482 × 108 ≈ 0.521 g. 11. When CuSO₄ solution is electrolysed, at anode:
- O₂ gas is evolved
- Dissociation of Cu takes place
- Metallic copper is deposited
- SO₂ gas is evolved
(a) Water oxidizes to O₂ at anode (2H₂O → O₂ + 4H⁺ + 4e⁻) since SO₄²⁻ is not oxidized. 12. Electrolysis of H₂O produces 4 ml of O₂ at NTP. Mass of H₂ gas produced is[KU 2008, BPKIHS 2007]
(a) 4 ml O₂ = 0.000178 mol ⇒ 0.000356 mol H₂ ⇒ Mass ≈ 0.000356 × 2 ≈ 0.01 g. 13. The conductivity of strong electrolyte:
- Increases slightly on dilution
- Decreases on dilution
- Doesn't change with dilution
- Depends upon the density of electrolyte
(a) Dilution increases ionic mobility, slightly increasing conductivity for strong electrolytes. 14. Three faradays of charge is supplied to bivalent metal. Number of electrons involved?[BPKIHS 1999]
- 18 × 10²³
- 6 × 10²³
- 2 × 10²³
- 9 × 10²³
(a) 3 F = 3 × 6.022×10²³ electrons = 18.066×10²³ ≈ 18 × 10²³ electrons. 15. How many faradays of charge is required to convert 1 mole of MnO₄⁻ to Mn²⁺?[I.E.]
(b) MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O ⇒ 1 mol MnO₄⁻ requires 5 F. 