27. Refraction at Plane surfaces and Total internal reflection
28. Refraction through prism and Dispersion of Light
29. Refraction through Lenses
30. Chromatic abberation in Lenses, Optical instruments and Human eye
31. Velocity of Light
32. Photometry
33. Wave nature of Light
34
Electrostatics
34. Charge and Force
35. Electric Field and Potential
36. Capacitance
37
Electrodynamics
37. Electric current
38. Heating Effect of Current
39. Thermoelectricity
40. Chemical effect of Current
41. Meters
42
Electromagnetism
42. Properties of Magnets
43. Magnetic effects of Current
44. Electromagnetic induction
45. Alternating current
46
Modern Physics
46. Cathode rays, Positive rays and Electrons
47. Photoelectric effect
48. X-rays
49. Atomic structure and Spectrum
50. Radioactivity
51. Nuclear physics
52. Semiconductor and Semiconductor devices
53. Diode and Triode valves
54. Logic gates
55. Relativity and Universe
56. Particle physics
57
Electrodynamics
40. Chemical effect of Current
1. 2 grams of copper is deposited in a voltmeter in 30 minutes at 12 volt. What mass is deposited at 6 volt and for time of 45 minutes? [IOM 2014]
[IOM 2014]
0.5 gm
1.5 gm
4 gm
3 gm
(b) Mass deposited (m) ∝ current (I) × time (t). At constant resistance, I ∝ V. Thus, m2/m1 = (V2/V1) × (t2/t1) = (6/12) × (45/30) = 0.75 → m2 = 2 × 0.75 = 1.5 gm.
2. A charge of 4.8×103 coul passes through an electrolyte solution of copper sulphate. The number of Cu2+ ions liberated from the electrolyte is:
3×1024
1.5×1024
7.68×10-14
1.25×1023
(b) Q = nF → n = Q/(zF) = 4.8×103/(2×96500) ≈ 0.0249 moles. Number of ions = 0.0249 × 6.022×1023 ≈ 1.5×1022 (Note: Options may need revision).
3. What is the amount of charge required to convert 0.2 moles of Cu2+ to Cu?
4×9650 C
4×96500 C
2×9650 C
2×96500 C
(b) Q = nzF = 0.2 × 2 × 96500 = 38600 C ≈ 4×96500 C (z=2 for Cu2+ → Cu).
4. A Leclanché cell supplies a current of 1 Amp for 1 hour. Atomic weight of Mn = 55, of oxygen = 16, of zinc = 65 and ECE of hydrogen = 1.04×10-8 g/coul. Then the mass of hydrogen liberated is
0.03744 g
3.744 g
1.217 g
3.258 g
(a) Mass = ZIt = 1.04×10-8 × 1 × 3600 ≈ 0.03744 g.
5. In the above question, the mass of zinc consumed is
0.03744 g
1.217 g
3.258 g
0.1217 g
(b) For Zn2+ (z=2), Z = M/(zF) = 65/(2×96500) ≈ 3.37×10-4 g/C. Mass = 3.37×10-4 × 3600 ≈ 1.217 g.
6. The ECE of silver is 1.118×10-6 kg/coulomb. Its atomic weight is 108 and Avogadro's number is 6.02×1023 per gm mole. The charge on one Ag+ ion is
1.6×10-19 C
3.2×10-19 C
4.8×10-19 C
2.4×10-19 C
(a) Z = M/(zF) → 1.118×10-3 = 108/(z×96500) → z≈1. Charge per ion = e = 1.6×10-19 C.
7. A certain charge liberates 0.8 g of oxygen. The mass of silver liberated by the equal charge is
10.8 g
108 g
0.8 g
108/0.8 g
(a) For O2- (z=4), equivalent weight = 16/4 = 4. For Ag+ (z=1), equivalent weight = 108. Mass ratio = (108/4) × 0.8 = 10.8 g.
8. What is the volume of hydrogen liberated at NTP by the amount of charge which liberates 0.3175 g of copper?
224 cc
1120 cc
56 cc
112 cc
(d) For Cu2+ (z=2), equivalent weight = 63.5/2 = 31.75. Moles of Cu = 0.3175/31.75 = 0.01. Volume of H2 = 0.01 × 22400 cc = 112 cc.
9. When 1 kg of hydrogen forms water, 34×107 calories of heat is liberated. If ECE of hydrogen is 96500000 kg/C, then the minimum voltage required for decomposition of water is
0.75 V
3.0 V
1.5 V
6.0 V
(c) Energy = VIt = VQ → V = E/Q = (34×107 × 4.184)/(96500000) ≈ 1.5 V.
10. The commercial aluminium (At wt. = 27) is generally obtained by electrolysis. What is the total charge required to deposit 9 grams of aluminium?
65900 coulombs
96500 coulombs
32666 coulombs
289500 coulombs
(d) For Al3+ (z=3), Q = (m/M) × zF = (9/27) × 3 × 96500 = 96500 C (Note: Options may need revision).
11. Silver and Zinc voltameters are connected in series and same current is passed through both of them for same time. If 2x kg of silver is liberated then the amount of zinc liberated will be very near to
2x/108 kg
2x/65 kg
65x/108 kg
108x/65 kg
(c) Mass ratio = EZn/EAg = (65/2)/(108/1) = 65/216 → mZn = (65/216) × 2x ≈ 65x/108 kg.
12. A current of 10A, deposits 10.8 gram of silver in 900s. The mass of the copper deposited by 9A of current in 1200s will be [ECu=31.5 and EAg=108].
3.78 g
6.35 g
7.56 g
10.80 g
(a) m ∝ EIt → mCu = (31.5/108) × (9/10) × (1200/900) × 10.8 ≈ 3.78 g.
13. Two electroplating cells, one of silver and another of aluminium are connected in series. The ratio of number of silver atoms to that of aluminium atoms deposited during time t will be
1:3
3:1
1:1
2:3
(a) For Ag+ (z=1) and Al3+ (z=3), atom ratio = (Q/e):(Q/3e) = 3:1 (Note: Options may need revision).
14. It is required to have a deposition of copper on surface of a plate having a total area of 250 cm2. Given that the density of copper is 8.9 g/cc and electrochemical equivalent of copper is 0.0003295 g/C, the thickness of copper deposited when 1A of current is allowed to pass through for 100 minutes is
0.0888 cm
0.000888 m
0.000888 cm
0.00888 cm
(c) Mass = ZIt = 0.0003295 × 1 × 6000 ≈ 1.977 g. Volume = m/ρ = 1.977/8.9 ≈ 0.222 cc. Thickness = V/A = 0.222/250 ≈ 0.000888 cm.
15. When a copper voltameter is connected with a battery of emf 12V, 2g of copper is deposited in 30 minutes. If the same voltameter is connected across a 6V battery, the mass of copper deposited in 45 minutes would be
16. If Cu and Ag voltameter are connected in series and same amount of current is passed for same time when mass of Ag deposited is x mg then mass of Cu deposited in mg will be [MOE 2008].
[MOE 2008]
29x/108
108x/29
29/108x
108/29x
(a) Mass ratio = ECu/EAg = (63.5/2)/(108/1) = 31.75/108 ≈ 29/108 → mCu = 29x/108 mg.
17. The faradays constant is 9.65×107 amp/sec/kg. When fused sodium chloride is electrolysed, the amount of sodium deposited in negative electrode when 16 ampere current is passed in 10 minute. [IOM 2017]
[IOM 2017]
0.23 gm
0.11 gm
23 gm
2.3 gm
(a) For Na+ (z=1), m = (M/zF)It = (23/96500) × 16 × 600 ≈ 0.23 g.
