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CBSE Class XII Important Questions Chemistry 2009

CBSE Important Questions
Class XII


Q. 1. Among the isomeric alkanes of molecular formula C5H12, identify the one that on photochemical chlorination yields (i) A single monochloride (ii) Three isomeric monochlorides. (1 mark)
Q. 2. While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason. (1 mark)
Q. 3. Write the IUPAC name of the following. (2 mark)
Q. 4. With the help of an example discuss the stereo chemistry involved in SN1 and SN 2 mechanism. (2 marks)
Q. 5. Explain Saytzeff rule by taking suitable examples. (2 marks)
Q. 6. Draw the structures of all isomeric alcohols of molecular formula C5H12O and give their IUPAC names. Classify these isomers of alcohols as primary, secondary and tertiary alcohols. (2 marks)
Q. 7. Nitro group increases the reactivity of chlorobenzene when attched to o and p- position but not at meta position? Explain? Write the mechanism also. (3 marks)
Q. 8. Account for the following. (3 marks)
  1. It is necessary to avoid even traces of moisture from a Grignard reagent.
  2. Chloroform is stored in closed dark coloured bottles completely filled.
  3. The carbon– oxygen bond length in phenol is slightly less than that in methanol.
Q. 9. (a) Explain the fact that in aryl alkyl ethers (i) the alkoxy group activates the benzene ring towards electrophilic substitution and (ii) it directs the incoming substituents to ortho and para positions in benzene ring. (2 mark)
(b) Arrange the following compounds in increasing order of their acid strength: (1 mark)
Propan-1-ol, 2,4,6-trinitrophenol, 3-nitrophenol, 3,5-dinitrophenol, phenol, 4-methylphenol
Q. 10. Give equations of the following reactions: (3 mark)
  1. Preparation of Sec-Butyl alcohol from ethanal
  2. Preparation of Phenol from Aniline.
  3. Treating phenol with chloroform in presence of aqueous NaOH.
Q. 11. How will you distinguish between the following: (3 marks)
  1. Propanoic acid and propanal
  2. Ethanal and Benzaldehyde
  3. Pentan-3-one and Pentan-2-one
Q. 12. How will you bring about the following conversions in not more than two steps. (5 marks)
  1. Propanone to Propene
  2. Benzene to m-Nitroacetophenone
  3. Chlorobenzene to benzoic acid
  4. Propanoic acid to propene
  5. Propyne to propan-2-ol
Q. 13. Explain the following with the help of suitable examples: (5 marks)
(a) Limitation of Williamsons synthesis (b) Stephen reaction. (c) Hell-Volhard-Zelinsky reaction (d) Aldol Condensation (e) Wolff-Kishner reduction.
Q. 14. (a) An organic compound (A) (molecular formula C8H16O2) was hydrolysed with dilute sulphuric acid to give a carboxylic acid (B) and an alcohol (C). Oxidation of (C) with chromic acid produced (B). (C) on dehydration gives but-1-ene. Write equations for the reactions involved
(b) Predict the products formed when cyclohexanecarbaldehyde reacts with following reagents.
  1. PhMgBr and then H3O+
  2. Tollens ’ reagent
Q. 15. Primary alkyl halide C4H9Br (a) reacted with alcoholic KOH to give compound (b). Compound (b) is reacted with HBr to give (c) which is an isomer of (a). When (a) is reacted with sodium metal it gives compound (d), C8H18 which is different from the compound formed when n-butyl bromide is reacted with sodium. Give the structural formula of (a) and write the equations for all the reactions.
(ii) Out of C6H5CH2Cl and C6H5CHClC6H5, which is more easily hydrolysed by aqueous KOH.
Q. 16. (a) Write the reactions of glucose with (i) HI (ii)HNO3 (iii)(CH3CO)2O
(b) Discuss the amphoteric nature of amino acid with suitable example.
Q. 17. (a) Discuss the following
  1. Denaturation
  2. invert sugar
  3. Globular proteins
(b) What is glycogen? How is it different from starch?
(c) Draw the cyclic structures of anomers of glucose.
Q. 18. (a) Compound A of molecular formula C3H7Br, yields a compound B of molecular formula C3H8O when treated with aq. NaOH. On oxidation the compound B yields a ketone C. Compound C on treating with methyl magnesium bromide and then H2O in acidic medium gives tertiary butyl alcohol. Deduce the structures of A, B and C and write the reactions involved. (3 marks)
(b) Draw the structures of major mono halo products in each of the following reactions. (2 marks)
(2 marks)
  1. Carboxylic acid is a stronger acid than phenol. Why? 2
  2. How will you convert ethanal into the following compounds? 2
    (i) Butane-1,3-diol
    (ii) But-2-enal
  3. Predict the products formed when cyclohexanecarbaldehyde reacts with Semicarbazide and weak acid (1 marks)
Q. 19. (a) Discuss the chemistry involved in Brown ring test for nitrate ion. Give equations also. 2 marks
(b) Complete the following equations: 3
  1. P4 + SOCl2 ---------------à
  2. 4 AgNO3 + 2H2O + H3PO4 -------------à
  3. NaCl + MnO2 + H2SO4 ------------------à
(a) Account For the Following: 3
  1. H3PO2 act as monobasic acid.
  2. Interhalogen compounds are more reactive than halogens
  3. Bond dissociation energy of F2 is smaller than Cl2.
(b) Discuss the quantitative method for estimating O3 gas. (2 marks)
Q. 20. (i) What are interstitial compounds? Why are such compounds well known for transition metals? (1 marks)
(ii) How is the variability in oxidation states of transition metals different from that of the non transition metals? Illustrate with examples. (1 marks)
(iii)Describe the preparation of potassium dichromate from iron chromite ore. What is the effect of increasing pH on a solution of potassium dichromate? (2 + 1 marks)
(i) Account for the following. (1 x 3 marks)
  1. Sc, the first member of first transition series doesn’t exhibit variable oxidation state. Account for the following
  2. Transition metals have a strong tendency to form complexes.
  3. Zirconium (atomic no 40) and hafnium (atomic no 72) exhibit similar properties.
(ii) How does acidified solution of potassium dichromate react with (a) FeSO4 and (b) H2S?

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