KENDRIYA VIDYALAYA SANGATHAN CHENNAI REGION COMMON PRE-BOARD EXAMINATION 2014-15

CLASS-XII CHEMISTRY

TIME:3HRS MAX.MARKS-70

Instructions:

Answer all the questions.

Questions 1 to 5are very short answer type and carry one mark each. Answer them in one

word or in one sentence.

Questions 6 to 10 are short answer type and carry 2 marks each. Answer them in 20 words.

Questions 11 to 22 are short answer type and carry 3 marks each. Answer them in 30

words.

Question 23 is value based question and carry 4 marks.

Questions 24 to 26 are long answer type and carry 5 marks each. Answer them in 50 to 60

words.

All 5 mark questions, one 3 mark question and one 2 mark question have internal choice.

There is no overall choice.

Use log book wherever needed. Use of calculator or any other electronic item is strictly

prohibited.

1. Write the IUPAC name of p-Cl C6H5CHO. (1)

2. What are Nucleosides? (1)

3. Ethers are highly volatile than alcohols. Give reason. (1)

4. Why are the diazonium salt formed by aliphatic amines unstable whereas that of aromatic

amines stable. (1)

5. What is the basic principle involved in zone refining method of purification of metals. (1)

6. In the Button cell, widely used in watches, the following reaction takes place:

Zn(s) +Ag2O(s) + H2O → Zn+2(aq) + 2Ag(s)+ 2OH-(aq)

CalculateE0cell and standard Gibbs energy for the reaction.

(Given: E0Ag+ / Ag = + 0.80 V ; E0

Zn+ / Zn = - 0.76 V )(2)

OR

What is meant by over voltage and electro chemical equivalent in electro chemistry?

7. Haloarenes are less reactive than haloalkanes towards nucleophilic substitution reactions.

Give two reasons. (2)

8. Distinguish between- (2)

a. Pentan-3-one and Pentan-2-one.

b. Ethanal and propanol.

9. What type of deviation from ideal behavior does chloroform and acetone mixture show?

Explain. (2)

10. Write one example each for Finkelstine reaction and Wurtz reaction. (2)

11. Explain the following with example-

a. Cationic detergents b. Broad spectrum antibiotics c. Food preservatives. (3)

12. What is hydrometallurgy? Why is cryolite added to alumina in the extraction of ‘Al'? Why is

CaCO3 added in blast furnace of extraction of iron? (1+2)

13. Draw the structure of- a. XeOF4 b. Pyrophosporic acid c. Sulphuric acid. (3)

14. An organic compound (A) (molecular formulaC8H16O2) was hydrolyzed 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. (3)

OR

An organic compound C9H10O forms 2,4-DNP derivative, reduces Tollens’ reagent and

undergoes Cannizzaro reaction. On vigorous oxidation, it gives 1,2-benzenedicarboxylic

acid. Identify the compound.

15. 1. Write the structure of monomers used for the preparation of Buna – N. (1+1+1)

2. What is vulcanization of rubber?

3. Give one example each for elastomer and fibrous polymer.

16. What is molar conductivity of an electrolyte? Calculate the equilibrium constant of the

reaction Cu(s) + 2Ag+(aq) Cu2+(aq) + 2Ag(s). Given that the E°Ag+/Ag = 0.8v and

E°Cu2+

/Cu= 0.34v. (1+2)

17. Differentiate between Lyophilic and lyophobic colloids. What is the significance of

Brownian movement in colloids? (1+2)

18. a. Explain on the basis of valence bond theorythat [Ni(CN)4]2- ion with square planar

structure is diamagnetic and the [NiCl4]2- ion with tetrahedral geometry is paramagnetic.

b.Drawadiagram to show the crystal field splitting of ‘d’orbital in tetrahedral field.(3)

19. a. How do you prove that glucose contains a 1° alcohol group?

b. What is a tripeptide?

c. Name the vitamin whose deficiency cause pernicious anemia.(1+1+1)

20. Define osmotic pressure of a solution. 18g of C6H12O6 is dissolved in 1kg of water in a

saucepan. At what temperature will water boil at 1.013bar? Kb for water is 0.52Kkgmol-1

21. a. How will you convert propan 1 ol topropan 2 ol? (3)

b. How will you distinguish between 1 phenyl ethanol to 2 phenyl ethanol?

22. Give reason –(3)

a. Aniline does not undergo Friedal Crafts reaction.

b. Gabriel pthalimide synthesis is not a suitable method to prepare aromatic primary

amine.

c. Aniline is less basic than ethanamine.

23. Raman and John are fruit sellers. Raman always arranges the fruits in an orderly fashion.

John keeps the fruits as a heap. As a student of science, does this make any difference to

you? What value does this add to your life? By seeing such orderly arrangement of fruits in

shops what differences are you reminded of quartz and quartz glass? Does it have any

impact in understanding why diamond is used as gemstone? (4)

24. Answer the following related to ‘d’ block elements:(5)

a. They posses high enthalpy of atomization.

b. They and their compounds act as catalyst.

c. They easily form alloys

d. They form complex compound.

e. They show magnetic character.

OR

a. Write one similarity and two differences between Lanthanides and actinides. (3)

b. Write equation for the reaction between KMnO4 and KI in acid and alkaline medium.(2)

25. a. Arrange the following in the increasing order of properties mentioned.(3)

i. H2Te, H2Se,H2O,H2S (Boiling point)

ii. PH3, NH3, SbH3, AsH3, BiH3 (Basic strength)

iii. HBr, HCl, HI, HF ( Acidic character)

c. Write the equations involved in the preparation of H2SO4 by contact process. (2)

OR

a. Explain why? (3)

i. S2 is paramagnetic in nature.

ii. O3 acts as a powerful oxidizing agent.

iii. 'He’ is used in diving apparatus.

b. How is PH3 purified? Write equation. (2)

26. a. What is order of a reaction? How does it differ from molecularity of the reaction? (2)

b. Calculate the rate constant of the reaction at 700K if the energy of activation for the

following reaction is 209kJ/mol and the rate constant at 600K is 1.60x10-5S-1.

C2H5I (g) C2H4(g) + HI(g) (3)

OR

a. What is pseudo first order reaction? Write one example. (2)

b. The following data were obtained during the first order thermal decomposition of

N2O5(g) at constant volume.2N2O5(g) 2N2O4(g)+O2(g)

(3)

Sl.No. Time/s Total Pressure/(atm)

1. 0 0.5

2. 100 0.512

Calculate the rate constant.

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