CBSE Chemistry Practice Paper for Class XII Board Exam

CHEMISTRY, CLASS :XII, MAX.MARKS : 70, TIME : 3Hrs.

INSTRUCTIONS:

* Answer all the questions:

* Questions 1 to 8 carry one mark each. Answer them in one word or a sentence.

* Questions 9 to 18 carry 2 marks each. Answer them in 20 to 30 words.

* Questions 19 to 27 carry 3 marks each. Answer them in 40 to 50 words.

* Questions 28 to 30 carry 5 marks each. Answer them in 70 words.

* There is no overall choice. However there is internal choice in one question each

of two mark and three marks questions. All 5 marks questions have internal

choice.

* Calculator or any other electronic items are not allowed. However logarithm

book may be used for calculations.

1. Blood cells collapse when suspended in saline water. Give reason. (1)

2. Why is shape selective catalyst highly specific? (1)

3. What is the difference between pig iron and cast iron in terms of amount of

carbon present? (1)

4. Write one example each for homoleptic and heteroleptic complexes. (1/2 +1/2)

5. Write the IUPAC name of (1)

clip_image001

clip_image002clip_image002[1]clip_image003clip_image004 CH3 OC2H5

6. When benzoic acid is treated with CH3Cl and anhydrous AlCl3 ring substitution

doesn’t take place. Why? (1)

7. How do you convert ethanamide to methanamine? Write balanced equation

only. (1)

8. Name the linkage connecting the nucleotide units in DNA. (1)

9. Define the terms a) Unit cell b) Co-ordination number of a particle in close

Packing. (2)

(OR)

Write an example of intrinsic semi conductor? How can you increase their

conductivity?

10. If sodium is present in a simple cubic lattice and the radius of one atom is

100pm, calculate the packing efficiency of the crystal. (2)

11. Calculate the mass of Ascorbic acid (C6H8O6) to be dissolved in 75g of acetic

acid to lower its melting point by 1.5°C.kf = 3.9 K Kg Mol-1. (2)

12. State Raoult’s law for the solution containing non-volatile solute. What type of

deviation is shown by Ethyl alcohol and water solution. (1+1)

13. Differentiate between order of a reaction and molecularity of a reaction (2)

14. Give reason why? (1+1)

a) C is a better reducing agent for ZnO than CO above 805°C.

b) NaCN is used in froth floatation method of purification of PbS.

15. Draw the structure of (2)

a) S6 molecule b) HClO4 molecule

16. Write the IUPAC name of [Co(NH3)5(NO2)]Cl2. This compound can be prepared

in two different colored crystalline forms. What could be the structural

difference in the two forms? (1+1).

17. Complete the following reactions. (1+1)

clip_image005clip_image006clip_image007 a) 2 Cl + 2 Na Ether

clip_image008

clip_image009 b) C6H5 CH2 CH = CH2 + HBr

18. Write the SN1 Mechanism involved in the conversion of (CH3)3C-Br to

(CH3)3C- OH (2)

19. a) Draw the structure of activated complex formed when H2 & I2 react to form

HI. (1)

b) A wood piece found in a excavation site contain 75% of C14 content as the

fresh wood contain. If the half life period of C14 = 5730 years, find the age of

the wood. (2)

(OR)

a) In a reaction, 5g of a reactant reduced to 2.5g in 10 hr. When 10g of the (1)

reactant is taken, it took 20 hr to reduce to 5g. What is the order of the reaction?

b) For a first order reaction, the rate constant at 400K is 2.25×10-6 s-1. Calculate the rate constant at 500K if the activation energy for the reaction is 250KJ/mol.

20. a) Define the terms – (2)

i) Dialysis ii) peptisation

b) Which among the following is most suitable for coagulation of

Fe2O3.xH2O/Fe3+ colloid? Why? Al3+, PO43- , Na+, Br-. (1/2 +1/2)

21. a) Arrange the following in the decreasing order of the property mentioned.

H2Se, H2S, H2Te, H2O (Bond angle)

HClO2,HClO4, HClO, HClO3 (acidic character) (2)

b) H3PO2 (metaphosphoric acid) is a strong reducing agent. Write an equation to prove this property. (1)

22. i) Though F2 has less tendency to gain electron than Cl2 egH for Cl2 is more –ve

than that of F2), it is a strong oxidizing agent than Cl2. Why? (1)

ii) Why is He used in diving apparatus? (1)

iii) Why does NO2 dimerise? (1)

23. A colorless crystalline organic solid (A), having carbolic smell is acidic in

nature. ‘A’ when treated with Bromine water gives white precipitate (B). ‘A’

when treated with NaOH and CO2 followed by hydrolysis gives compound

(C).C can be used for the preparation of Aspirin. Identify A, B, C and write

equations for all changes. (3)

24. a)Gabriel phthalimide synthesis is not suitable for the preparation of Aniline.

Why? Write equation for the preparation of ethanamine by this method. (2)

b) Why is it necessary to acetylate aniline before nitration? (1)

25. a) Name the disease caused by the deficiency of vitamin E. (1)

b) Among 1°,2°,3°& 4° structures which structure decides whether the protein is

globular (or) fibrous? Which type of forces stabilize the 2° structure of protein?

c)How do you prove that glucose contain one primary alcohol group? (1+1)

26.a) Is PVC a thermo plastic (or) thermosetting plastic? Why is it called so? (1)

b) state whether the following polymer is condensation polymer or addition

polymer ? Write the structure and name of monomers involved in this polymer.

clip_image010clip_image011clip_image012clip_image010[1]clip_image011[1] ( NH CO NH CH2 )n (2)

27.a) What do you mean by Agonist and Allosteric inhibitors? (2)

b) Soaps do not work in hard water. Why? (1)

28. a) Write two advantages of fuel cell over other cells. (2)

b) Two electrolytic cells containing AgNO3 & CuSO4 solutions as electrolytes

are connected in series. If two amperes of current is passed through the solutions

for 8 min, What is the mass of silver & copper deposited? (Atomic weight of

Cu=63.5u & Ag=108u) (2)

c) When Iron electrode at standard conditions is connected to standard hydrogen electrode to measure its standard potential, Which electrode act as anode? Why?

(OR)

a) Calculate the cell potential (Ecell) of the voltaic cell which is represented as

Cr(s) / Cr3+(0.001M) // Cd2+ (0.01M) / Cd (s) (3)

Given that E°Cr3+ / Cr = – 0.74v & E°Cd2+ / Cd = – 0.40.

b) State Kohlrausch law of independent migration of ion and one of its use? (2)

29.a) What do you observe when K2MnO4 solution is acidified? support your

observation with equation. (2)

b) Answer the following related to d- Block elements-

i) For ‘Fe’ the third ionization potential is less than expected.

ii) Both Cr2+ and Mn3+ have d4 configuration but Cr2+ is reducing and Mn3+

is oxidizing. Why?

iii) d- Bolck elements & their compounds can act as catalyst. (3)

(OR)

a) What is lanthanoid contraction? Write its consequences? (2)

b) Actinoids show greater number of oxidation state than Lanthanoid. Why?(1)

c) D- block elements form complexes easily. Why? (1)

d) The enthalpy of atomization is high for d-block element than s-block elements. Why? (1)

30.a) Write one example each for i) Wolff-Kishner reduction. (2)

ii) Hell-Volhard Zelinsky reaction.

b) The pKa value for benzoic acid,4-nitrobenzoic acid, 4-methoxy benzoic acid

are 4.19,3.41,4.46 respectively. What do you suggest about the effect of

substituents on the acidic character of these compounds. (2)

e) Among Acetaldehyde and acetone which is more reactive towards nucleophilic addition reaction? Why? (1)

(OR)

a) Distinguish between the compound s using chemical test and write equation.

i)Benzoic acid & ethyl benzoate.

ii)Ethanal & propanal.

b) Write the equation for cross aldol condensation reaction between Benzaldehyde and acetaldehyde. (2)

c) Aldehydes & ketones have less boiling point than alcohols.Why? (1)

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