CBSE Guess paper class XII Informatics Practices 2008 3


Guess Paper – 2008
Class – XII
Subject – Informatics Practices

Time: Three Hours Max. Marks: 70

General Instructions

1. All questions are compulsory.

2. Question nos. 1 to 8 are very short answer questions and carry 1 mark each.

3. Question nos. 9 to 18 are short answer questions and carry 2 marks each.

4. Question nos. 19 to 27 are also short answer questions and carry 3 marks each.

5. Question nos. 28 to 30 are long answer questions and carry 5 marks each.

6. Use log tables if necessary, use of calculators is not allowed.

  1. Mention one property which is caused due to presence of F –centre in a solid?
  2. The decomposition reaction of ammonia gas on platinum surface has a rate constant = 2.5 x 10-4 mol L-1 S-1. What is the order of the reaction?
  3. Give the IUPAC name of the following compound:(CH3)2NHC2H5
  4. What is the effect of Schottky defect and Frenkel defects on the density of crystals.
  5. A reaction is first order in A and second order in B. How is the rate affected when the concentration of both A and B is doubled.
  6. Give the structure of : 4 - methyl pent -3- en - 2 – one
  7. In the ring test for identification of nitrate ion, what is the formula of the compound responsible for the brown ring formed at the interface of two liquids?
  8. Except for vitamin B12, all other vitamins of group B, should be supplied regularly in diet. Why?
  9. Niobium crystallizes in body –centered cubic structure .if density is 8.55 g/cm3 .calculate atomic radius of niobium using its atomic mass 93 u.
  10. How do you account for conductivity of strong and weak electrolyte with concentration? Plot the graphs also.
  11. Differentiate between the following: (a) Lyophobic & Lyophilic sol
  12. Explain the following observations:

(a) An electrolyte NaCl is added to hydrated ferric oxide

(b) Electric current is passed through a colloidal sol.

13.(a) Describe Brown ring Test.

(b) R3P=O exist but R3N=O does not. Why

OR

(a)Ozone (O3) acts as a powerful oxidising agent. Why

(b)Sulphur vapours exhibits paramagnetism.Why

14. (a) How can you convert an amide into an amine having one carbon less - than the starting compound? Name the reaction.

(b) Accomplish the following conversions:

Nitrobenzene to Aniline

15. (a) ICl is more reactive than Cl2.why

(b) The acidic strength of oxoacids of halogens varies in the order:

HClO4> HClO3> HClO2> HClO. Why

16. Give one chemical test to distinguish:

(a) Phenol and Benzoic Acid

(b)Propanal and propanone

17. Write the mechanism of the following reactions

nBuBr + KCN à nBuCN

18. Give example for following name reaction:

(a) Hell Volhard Zelinsky Reaction

(b)Rosenmund Reduction

19. Calculate the standard free energy change for the following reaction at 250C

Au(s) +Ca+2 (1 M)à Au3+(1M) + Ca (s)

The electrode values are Ca2+ / Ca = –2.87V Au3+ / Au = +1.50V

Predict whether the reaction will be spontaneous or not at 250C which of the above two half cells will act as an oxidizing agent and which one will be a reducing agent?

(b) When a current of 0.75A is passed through a CuSO4 solution for 25 min, 0.369g of copper is deposited at the Cathode. Calculate the atomic mass of copper.

20. (a) For a first order reaction, show that time required for 99% completion is twice the time required for the completion of 90% of reaction.

(b) Sucrose decomposes in acid solution into glucose and fructose according to the first order rate law, with t1/2 = 3.00 hours. What fraction of sample of sucrose remains after 8 hours?

21. (a) Describe a method for refining of Nickel or Zirconium.

(b) What is the role of cryolite in the metallurgy of aluminium?

22. Complete the following equations:

(a)XeF4 + H2Oà

(b) XeF6 +H2O à

(c)Write the balanced equations involved in the preparation of PH3.

23. Give the electronic configuration of the

(a) d- orbital’s of Ti in [Ti (H2O)6]3+ ion in an octahedral crystal field.

(b) Why is this complex coloured? Explain on the basis of distribution of electrons in the d- orbitals.

(c) How does the colour change on heating [Ti (H2O)6]3+ ion?

24. (a) The treatment of alkyl chlorides with aq.KOH leads to the formation of alcohols but in the presence of alc.KOH alkenes are major products.

(b)Haloalkanes react with KCN to form alkyl cyanides as main product while AgCN forms isocyanides as main product.

25. (a) Write a note on zwitter ion.

(b) What is the effect of Denaturation on the structure of proteins?

(c) Write the important differences between DNA and RNA

26. Write the structure of monomer& uses each of Buna-S Dacron, Bakelite, and PHBV.

27. Define the following terms giving suitable examples: Tranquilizers ,Antifertility drugs Antihistamines Artificial sweeteners, Antiseptics & Disinfectants

OR

27. Account for the following:

(a) Aspirin drug helps in the prevention of heart attack.

(b) Diabetic patients are advised to take artificial sweetners instead of natural sweetners.

(c) Detergents are non-biodegradable while soaps are biodegradable.

(d) The is use of aspartame limited to cold drinks and foods?

28. (a) Derive the relationship between relative lowering of vapour pressure and mole fraction of the volatile liquid.

(b) (i) Benzoic acid completely dimerises in benzene. What will be the vapour pressure of a solution containing 61g of benzoic acid per 500g benzene when the vapour pressure of pure benzene at the temperature of experiment is 66.6 torr?

(ii) What would have been the vapour pressure in the absence of dimerisation?

(iii) Derive a relationship between mole fractions and vapour pressure of a component of an ideal solution in the liquid phase and vapour phase.

OR

28. (a) Which aqueous solution has higher concentration -1 molar or 1 molal solution of the same solute? Give reason.

(b) 0.5g KCl was dissolved in 100g water and the solution originally at 200C, froze at – 0.240C. Calculate the percentage ionization of salt. Kf per 1000g of water = 1.86K.

29. (a) Out of Ag2SO4, CuF2 , MgF2 and CuCl, which compound will be coloured and why?(b) Explain :

(i) CrO42- is a strong oxidizing agent while MnO42 is not.

(ii) Zr and Hf have identical sizes.

(iii) The lowest oxidation state of manganese is basic while the highest is acidic.

(iv) Mn (II) shows maximum paramagnetic character amongst the divalent ions of the first transition series. 5

OR

29. (a) In the titration of FeSO4 with KMnO4 in the acidic medium, why is dil H2SO4 used instead of dil HCl?

(b) Give reasons:

(i) Among transition metals, the highest oxidation state is exhibited in oxoanins of a metal.

(ii) Ce4+ is used as an oxidizing agent in volumetric analysis.

(iii) Transition metals form a number of interstitial compounds.

(iv) Zn2+ salts are white while Cu2+ salts are blue.

30. An unknown Aldehyde ‘A’ on reacting with alkali gives a -hydroxy –aldehyde, which losses water to form an unsaturated aldehyde, 2- butenal. Another aldehyde ‘B’ undergoes disproportionation reaction in the presence of

conc. alkali to form products C and D. C is an arylalcohol with the formula C7H8O.

(i) Identify A and B.

(ii) Write the sequence of reactions involved.

(iii) Name the product, when ‘B’ reacts with Zinc amalgum and hydrochloric acid.

OR

An organic compound (A) having molecular formula C8H8O forms an orange red precipitate (B) with 2, 4 – DNP reagent. Compound (A) gives a yellow precipitate (C) when heated in the presence of iodine and NaOH along with a colourless compound (D). (A) does not reduce Tollen’s reagent or Fehling’s solution nor does it decolorize bromine water. On drastic oxidation of (A) with chromic acid, a carboxylic acid (E) of molecular formula C7H6O2 is formed. Deduce the structures of the organic compounds (A) to (E).

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