CBSE Question Paper 2015 class 12 Chemistry

General Instructions:

(i) There ae total of 26 questions in all. All questions are compulsory.
(ii) Question numbers 1 to 5 are very short answers questions carrying 1 mark each.
(iii) Question numbers 6 to 10 are short answers questions carrying 2 marks each.
(iv) Question numbers 11 to 22 are also short answer questions carrying 3 marks each.
(v) Question number 23 is value based question carrying 4 marks.
(vi) Question numbers 24 to 26 are long answer questions carrying 5 marks each.

1. Which stoichiometric defeat in crystals increases the density of a solid?

2. What is meant by ‘shape selective catalysis’ of reactions?

3. Which of the following is more stable complex and why?

 and

4. Write the IUPAC name of the following compound:

5. Which would undergo  reaction faster in the following pair and why?

and

6. State Raoult’s law for the solution containing volatile components. What is the similarity between Raoult’s law and Henry’s law?

OR

Determine the osmotic pressure of a solution prepared by dissolving  of  in 2L of water at C, assuming that is completely dissociated.
(R = 0.0821 L atm  , Molar mass of  = 174 g mol)

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

8. How do you prepare?
(a)  from ?
(b)  from ?

9. Write the mechanism of the following reaction:

10. Arrange the following in the decreasing order of given property indicated:
(a)  and
(b)  and

11. (a) What type of semiconductor is obtained when silicon is doped with boron?
(b) What type of magnetism is shown in the following alignment of magnetic moments?

(c) What type of point defect is produced when AgCl is doped with ?

OR

Niobium crystallises in body-centred cubic structure. If density is 8.55g , calculate atomic radius of niobium using its atomic mass as 93u.

12. 3.9g of benzoic acid dissolved in 49g of benzene shows a depression in freezing point of 1.62K. Calculate the Van’t Hoff factor and predict the nature of solute (associated or dissociated).
(Given: Molar mass of benzoic acid = 122g , for benzene = 4.9 K kg )

13. (a) What do you understand by the ‘order of reaction’? Identify the reaction order from each of the following units of reaction rate constant:
(i)
(ii)
(b) Give one example of zero order reaction.

14. Explain the following terms:
(a) Tyndall effect
(b) Dialysis
(c) Electrophoresis

15. Write the principles of the following methods:
(a) Froth flotation method
(b) Electrolytic refining
(c) Zone refining

16. Complete the balance the following chemical equations:
(a)  + NaOH (hot and conc.)
(b)
(c)

17. (a) Name the element of 3d transition series which shows maximum number of oxidation state.
(b) Name a member of the lanthanoid series which is well-known to exhibit +2 oxidation state.
(c) Complete the equation:

18. (a) Draw the geometrical isomers of complex compound
(b) On the basis of crystal field theory, write the electronic configuration for  ion if
(c) Write the hybridization and magnetic behaviour of the complex compound

19. Give reasons for the following:
(a) The presence of nitro group  at ortho or Para positions increases the reactivity of haloarenes towards nucleophilic substitution reactions.
(b) Racemic mixture is optically inactive.

20. Give the structure of A, B and C in the following rections:
(a)  – Br  A  B  C
(b)   A  B  C

21. (a) Deficiency of which vitamin causes scurvy?
(b) What type of linkage is responsible for the formation of proteins?
(c) Write the product formed when glucose is treated with HI.

22. (a) What are disinfectants? Give an example.
(b) Give two examples of macromolecules that are chosen as drug targets.
(c) What are anionic detergents? Give an example.

23. After the ban on plastic bags, students of one school decided to make the people aware of the harmful effects of plastic bags on environment and Yamuna river. To make the awareness more impactful, they organized rally by joining hands with other schools and distributed paper bags to vegetable vendors, shopkeepers and departmental stores. All students pledged not to use polythene bags in future to save Yamuna river.
After reading the above passage, answer the following questions:
(a) What values are shown by the students.
(b) What are biodegradable polymers? Give one example.
(c) Is polythene a consideration or an addition polymer.

24. (a) Explain the following observations:
(i) The products of electrolysis of molten NaCl are sodium metal and chlorine gas.
(ii) The products of electrolysis of aqueous sodium chloride are NaOH,  and
(b) The molar conductivities of  ion and  ion are 73.5 s  and 76.25 s respectively. The specific conductivity of 0.1M  is  s . Calculate the dissociated constant of

OR

(a) Describe the principle and overall reaction involved in the working of hydrogen-oxygen fuel cell.
(b) Write the Nernst equation and calculate the emf of the following cell at 298K:
Cu(s)/  (0.13M)   (M) /Ag(s)

25. Assign a possible reason for the following:
(a) Fluorine forms only one oxoacid HOF.
(b) Nitrogen exist as diatomic  while phosphorus exist as tetratomic  at room temperature.
(c) The negative value of the electron gain enthalpy of fluorine is less than that of chlorine.
(d) Interhalogen compounds are more reactive than halogens.
(e)  is a monoprotic acid.

OR

(a) Give reasons for the following:
(i) has lower boiling point than
(ii) Oxygen shows catenation behaviour less than Sulphur.
(iii) Helium is used in diving apparatus.
(b) Draw the structures of the following molecules:
(i)
(ii)

26. (a) Give simple chemical tests to distinguish between the following pairs of compounds:
(i) Proponal and propanone
(ii) Benzaldehyde and acetaldehyde

(b) Write the products of the following reactions:
(i)  NCONHN 
(ii)  conc. NaOH
(iii)

OR

(a) Account for the following:
(i)  is more reactive than  towards reaction with HCN.
(ii) Carboxylic acid is stronger acid than phenol.
(b) Identify A, B and C in the following sequence of reactions:
  A  B  C

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