St.brittos matric hr. Sec . school
Pre-half yearly exam
Chemistry
Choose the correct answer :
Std 12
Part I
Max marks: 150
1. The value of Bohr radius for hydrogen atom is
a) 0.529 × 10-8 cm b) 0.529 × 10-10 cm c) 0.529 × 10-6 cm d) 0.529 × 10-12 cm
2. The bond order of oxygen molecule is
a) 2.5 b) 1 c) 3 d) 2
3. The hybridisation in PCl5molecule is
a) sp3 b) sp3d2 c) sp3d d) sp3d3
4. Among the following which has the maximum ionisation energy
a) Alkali elements b) Alkaline elements c) Halogens c) Noble gases
5. The bond length of Cl2 molecule is
a) 0.74 b) 1.44 c) 1.98 d) 2.28
6. When XA>>XB, A–B bond is
a) polar covalent b) non-polar covalent c) Ionic d) metallic
7. One can draw the map of building on a glass plate by
a) HI b) HF c) HBr d) HCl
8. The lightest gas which is non-inflammable is
a) He b) H2 c) N2 d) Ar
9. The compound with garlic odour is
a) P2 O3 b) P2O5 c) H3PO3 d) H3PO4
10. Silver salt used in photography is
a) AgCl b) AgNO3 c) AgF d) AgBr
11. Which of the following compounds is not coloured?
a) Na2CuCl4 b) Na2CdI4 c) K4 [Fe(CN)6] d)K3[Fe(CN)6]
12. Which transition element show highest oxidation state
a) Sc b) Ti c) Os d) Zn
13. The Lanthanides contraction is due to
a) Perfect shielding of 4f electron b) Imperfect shielding of 4f electron
c) Perfect shielding of 3d electron d) Imperfect shielding of 3d electron
14. _______form oxocations
a) Lanthanides b) Actinides c) Noble gases d) Alkalimetals
15. Lanthanides are separated by
a) Fractional distillation b) Steam distillation c) Fractional Crystallisation d) Sublimation
16. The coordination number of Ni(II) in [Ni(CN)4] is
a) 2 b) 4 c) 5 d) 6
17. Paramagnetic moment is expressed in
a) Debye unit b) K Joules c) BM d) ergs
18. Valence bond theory does not explain the property of complex compound
a) geometry b) magnetic c) nature of ligand d) colour
19. In the nuclear reaction, 92U238 → 82Pb206, the number of α and β particles emitted are
a) 7α, 5β b) 6α, 4β c) 4α, 3β d) 8α, 6β
20. Which of the following is used as neutron absorber in the nuclear reactor?
a) Water b) Deuterium c) Some compound of uranium d) Cadmium
21. Which one of the following particles is used to bombard 13Al27 to give15p30 and a
neutron
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a) α particle b) deuteron c) proton d) neutron
22. In the Bragg’s equation for diffraction of X-rays ‘n’ represents
(a) The number of moles (b) Avogadro number
(c) A quantum number (d) Order of reflection
23. Rutile is
(a) TiO2 (b) Cu2O (c) MoS2 (d) Ru
24. An example of metal deficiency defect
(a) NaCl (b) AgCl (c) CsCl (d) FeS
25. All the naturally occuring processes proceed spontaneously in a direction which leads to
a) decrease of entropy b) increase in enthalpy
c) increase in free energy d) decrease of free energy
26. In which of the following process, the process is always non-feasible?
a) ΔH > 0, ΔS > 0 b) ΔH < 0, ΔS > 0 c) ΔH > 0, ΔS < 0 d) ΔH < 0, ΔS < 0
27. The reaction of Lucas reagent is fast with
(a) (CH3)3COH (b) (CH3)2CHOH (c) CH3(CH2)2OH (d) CH3CH2OH
28. An equilibrium reaction is endothermic if K1 and K2 are the equilibrium constants at T1
and T2 temperatures respectively and if T2 is greater than T1 then
a) K1 is less than K2 b) K1 is greater than K2 c) K1 is equal to K2 d) None
29. The alcohol obtained by the hydrolysis of oils and fats is
(a) pentanol (b) propanol (c) glycerol (d) glycol
30. The rate constant of the forward reaction and reverse reaction are 8X10-5 and 2X10-4
respectively. The Kc is –
a) 0.004 b) 0.02 c) 0.2 d) 0.4
Part II
Answer any 15 questions
15x3=45
31. Distinguish between particle and wave.
32. If C-Cl bond distance is 1.76 A° and atomic radius of chlorine is 0.99 A°, calculate the
Atomic radius of Carbon.
33. Write a note on plumbo solvency?
34. Why transition elements from complexes?
35. Account for the following :
(a) lower members of alcohols are soluble in water but higher members are not
(b) Alcohols cannot be used as solvent for grignard reagent.
36. A substance is found to have a magnetic moment of 3.9 BM. How many unpaired
electrons does it Contain?
37. What is binding energy of Nucleus?
38. Write a short note on metallic crystals.
39. What is entropy? What are the units of entropy?
40. Define – Reaction quotient ‘Q’.
41. Why He2 is not formed?
42. Calculate the effective nuclear charge experienced by the 4s electron in potassium atom.
43. What are inter halogen compounds? How are they formed?
44. What happens when KI solution is added to an aqueous solution of copper sulphate?
45. Wooden artifact and freshly cut tree are having 7.6 and 15.2 counts min-1g-1 of carbon
(t½ = 5700 years) respectively. Calculate the age of the artifact.
46. The diffraction of a crystal with X-ray of wavelength 2.31A° gives a first order reflection
at 28°.9. What is the distance between the diffracted planes.
47. Mention the essential condition for spontaneity in a chemical reaction.
48. Calculate Δng, for the following reactions
49. H3PO3 is diprotic. Why?
50. How is allyl alcohol obtained from glycerol?
51. Write short notes on alumino thermic process?
PART – III
Answer any seven questions
7×5 = 35
52. Derive de-Broglie’s equation. What is its significance?
53. Explain how potassium dichromate is extracted from chromite ore.
54. Bring out the consequences of lanthanide contraction.
55. Write the postulates of werner’s theory.
56. State various statements of second law of thermodynamics.
57. State Le chatlier’s principle. How this principle used for the formation of NH3
58. Explain the formation of O2 molecule by molecular orbital theory.
59. List the ores of silver. How silver is extracted from Argentite?
60. Describe the extraction of Lanthanides from monozite sand.
61. In what way [FeF6] differs from [Fe(CN)6]
62. Explain Characteristics of Free energy ‘G’
63. Derive the expressions for Kc and Kp for decomposition of PCl5.
Part IV
Question No. 70 compulsory and answer any three from the remaining questions.
4×10=40
64. (a) Explain the various factors that affect ionisation energy.
(b) Mention the uses of silicones.
65. (a) Write the postulates of VB theory.
(b) Explain radio carbon dating
66. (a) Explain the nature of glass.
(b) Explain Braggs spectrometer.
67. (a) explain paulings scale of electronegativity.
(b) Describe in detail how noble gases are isolated from air?
68. (a) explain the isomerism in coordination compounds
(b) Differentiate chemical reactions from nuclear reactions.
69. (a) explain schottky and frenkel defects.
(b) Explain the Applications of electronegativity
70. a) An organic compound ‘A’ (C2H6O) reacts with metallic sodium liberates hydrogen
gas and also gives red color in victor Mayer test. On oxidation with K2Cr2O7 ‘A’gives
the compound ‘B’. ‘B’ also undergoes aldol condensation . Further oxidation of ‘B’
gives compound ‘C’ compound ‘A’&’C’ reacts in the presence of H2SO4 it gives
compound ‘D’ compound ‘D’ is fruity odour in nature. Identify compound A,B,C, and
D. Explain the reactions.
(b) An element A belongs to group number 12 and period number 4, bluish white in colour
reacts with conc.H2SO4 to give its salt B with the liberation of SO2 gas. Compound B
reacts with sodium bicarbonate to give C which is used as ointment for curing skin
diseases. Identify A, B and C and explain the reactions.
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