CBSE Board Sample Paper – 2011
Class – 12th
Subject –Chemistry
Time: 3 Hrs Max Marks: 70
General Instructions:
i. All questions are compulsory.
ii. Questions 1 to 8 are very short answer type carrying 1 mark each. Answer them in one sentence each.
iii. Questions 9 to 18 are short answer type carrying 2 marks each. Answer each of them in about 30 words.
iv. Questions 19 to 27 are also short answer type carrying 3 marks each. Answer each of them in about 40 words.
v. Questions 28, 29 & 30 are long answer type carrying 5 marks each. Answer each of them in about 70 words.
vi. Calculators are not permitted. Use log tables if necessary.
Section-A
1. The value of DfGo for formation of Cr2O3 is – 540 kJ mol-1 and that of Al2O3 is – 827 kJ mol- Is the reduction of Cr2O3 possible with Al? 1
2. What is oxidoreductase? 1
3. What is common in hcp and ccp types of solids? 1
4. Write IUPAC name of the ionization isomer of: [Cr (NH3)5 Br] SO4 . 1
5. A reaction is 50% complete in 2 hours and 75% in 4 hours what is order of the reaction? 1
6. What do you understand by term glycosidic linkage? 1
7. Write the product of electrolysis of AgNO3 by using silver electrode. 1
8. Why N2 is less reactive than P4? 1
Section-B
9. Aluminium crysatlises in a cubic close packed structure .its metallic radius is 125pm
a. What is length of side of the unit cell. 1
b. How many unit cells are there in 1 meter cube of aluminium. 1
10. R of 1 molar common salt solution filled in a cylindrical container having length 10 cm and radius 4 cm is 500 ohm find the conductivity of solution. 2
11. A reaction is first order w.r.t. A and second order with respect to B. 1.Write the differential rate equation .2.How is the rate of reaction affected if concentration of B is increases three time. 2
12. Sulphur in vapor state exhibit paramagnetic behavior. Explain. 2
13. What is lanthanide contraction ? 2
14. Account for the following
a. Chlorine water has both oxidizing and bleaching properties. 1
b. On addition of ozone ga to ki aolution,violet vapors are obtained. 1
15. Corrosion is essentially an electrochemical phenomenon .with the help of diagram explain the reactions occurring during the corrosion of iron. 2
16. “The extraction of Ag by leaching with NaCN involves both oxidation and reduction”. Explain? 2
17. Explain the following:
(i) Clemenson reduction (ii) Diazotization 2
18. Which oxide of sulphur is capable of acting as oxidizing as well as reducing agent? Why? 2
19. (a) What are the classes of neurologically active drugs? Write one example for each. 3
(b) What is the use of sodium benzoate in food?
20. (i) Calculate the emf of the cell in which the following reaction takes place. 3
Ni (s) + 2 Ag+ (0.002 M) → Ni 2+ (0.160 M) + 2 Ag (s)
Given that E0Cell = 1.05V
(ii) What are the products obtained at anode and cathode when aqueous NaCl is is electrolyzed with Pt electrodes?
21. (i) Which metal in the 1st transition series exhibits +1 oxidation state most frequently and why? 3
(ii) Write down the number of 3d electrons in each of the following ions:
Ti2+, V2+, Cr3+, Mn2+, Fe2+, Co3+, Co2+, Ni2+ and Cu2+
Indicate how the five d orbital's are to be occupied for these hydrated ions (Octahedral)
22. (a) How do you explain the amphoteric nature of amino acids. 2
(b) Write reaction when glucose is treated with acetic anhydride. 1
23. During a nuclear explosion ,one of the product is 90sr with the half life of 28.1 years .if 1ug of 90sr was absorbed in the bones of newly bone baby instead of calcium ,how much of it will remain after 10 years and 60 years if it is not lost metabolically. 3(please refer question no. 17 from ncert for proper statement in terms of symbols). 3
24. (a) In a given series the difference in the ionization enthalpies between any two successive d block elements is very much less than that in case of s and p block elements. Give the explanation. 3
(b) Transition elements exhibit highest oxidation states in oxides rather than in fluorides. Why?
(c) An yellow translucent solution is obtained on passing H2S gas through an acidified solution of KMnO4. Identify the solution and write the balanced chemical equation.
25. A copper-silver cell is set up . The copper ion concentration in it is 0.10 m. The concentration of silver ion is not known. The cell potential measured is 0.422v determine the concentration of silver ion in the cell. 3
26. How do you account for reducing nature of H3PO2 on the basis of its structure? 3
27. Silver crystallizes in F.c.c. ,if edge length is 4.07 x10-8 cm and density is 10.5 g/cm3 calculate the Atomic mass of silver. 3
Section-C
28. (a) The rate of reaction, 2NO + Cl2 → 2NOCl , is doubled when concentration of Cl2 is doubled and it becomes eight times when concentration of both NO and Cl2 are doubled. Deduce the order of the reaction.
(b) The time required for 10% completion of a first order reaction at 298 K is equal to that required for its 25% completion at 308K. If the pre-exponential factor for the reaction is 3.56 x 109 sec-1, calculate its rate constant at 318K and also the energy of activation. 5
OR
(a) Discuss the chemistry involved in Brown ring test for nitrate ion. Give equations also. 2
(b) Complete the following equations: 3
(i) P4 + SOCl2 --------------- →
(ii) 4 AgNO3 + 2H2O + H3PO4 ------------- →
(iii) NaCl + MnO2 + H2SO4 ------------------ →
29. (i) An unknown aldehyde A, C7H6O on reaction with KOH gives B and C. A reacts with Zn-Hg and conc HCl to give D which changes to A by CrO2Cl2. B on heating with soda lime gives E. identify A to E and write all reactions.
(ii) Write equations for:
(a) Cross aldol condensation between propanal and ethanal in the presence of dil NaOH
(b) Preparation of 2-methyl propan-2-ol from a Grignard reagent. 5
OR
(i) Account for the following 1 x 3+2
(a) Sc, the first member of first transition series doesn’t exhibit variable oxidation state.Account for the following
(b) Transition metals have a strong tendency to form complexes.
(c) Zirconium (atomic no 40) and hafnium (atomic no 72) exhibit similar properties.
(ii) How does acidified solution of potassium dichromate react with (a) H2C2O4 and (b) KI?
30. (a) Derive an expression to express the realtive lowering of vapour pressure for a solution is eaqual to the mole fraction of the solute in it whne the solvent alone is volatile. 3
(b) The elements a and b form purely covalent compounds having molecular formula ab2 and ab4.when dissolved in 20 g of benzene,1 g of ab2 lowers the freezing point by 2.3 k whereas i g of ab4 lowers it by 1.3k. The molal depression constant for benzene is 5.1k kg/mol calculate the atomic mass of a and b. 2
OR
(a) Account For the Following: 3
(i) H3PO2 act as monobasic acid.
(ii) Interhalogen compounds are more reactive than halogens
(iii) Bond dissociation energy of F2 is smaller than Cl2.
(b) Discuss the quantitative method for estimating O3 gas. 2