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. Define the maximum boiling point azeotrope. 1
2. What is the nature of crystral defect produced when sodium chloride is doped with magnesium chloride? 1
3. People living at high altitude generally suffer from anoxia , Explain. 1
4. Define the term mutarotation. 1
5. Give one example each of a triclinic and rhombohedral crystal type. 1
6. Write the structure of 1,4-Dibromobut-2-ene. 1
7. Why LiCl acquires pink colour when heated in Li vapours ? 1
8. Differentiate between chirality and chiral centre. 1
Section – B
9. Write the difference between physisorption and chemisorptions.
10. Write chemical equations for the following
i. Orthophosphorus acid is heated. 1
ii. Ptf6 and xenon are mixed together. 1
11. (i) Why are transition metal compounds coloured? 2
(ii) Although Sc is the first transition element, its compounds are colourless. Why?
12.What do you mean by activity and selectivity of catalysts?
13. Halo alkanes have higher boiling point than the corresponding parent alkane.
14. Give IUPAC names of following.
i. o- BrC6H4 CH( CH3) CH2 CH3
ii. m - Cl C6H4 CH2C (CH3)3
15. State what are : 2
(i) Henry’s law ?
(ii) relative lowering of vapour pressure ?
16. Calculate the freezing point of a one molar aqueous solution of KCl. [ Density of the solution = 1.04 g/cc. , Kf = 1.86 K Kg mol-1 , At wt. of K = 39 and Cl = 35.5] 2
17. State what are : 2
(i) Hypotonic solution ?
(ii) Azeotropes ?
18. Explain how an –OH group attached to a carbon atom in the benzene ring activates it towards electrophilic substitution. 2
Section – C
19. a) How is colloidal sol. of sulphur is prepared?
b) Define gold number. What does receprocal of gold number indicate?
c) Give one test to distinguish whether the given emulsion is oil in wtaer type or water in oil type emulsion. 3
20. Account for following: 3
a) Dehydration of alcohols to form alkenes is always carried out with conc.H2SO4 and not with conc.HNO3.
b) Ditertiary butyl ether cannot be prepared by Williamson’s synthesis.
c) Hydrzones of CH3CHO are not prepared in highly acidic medium
21. Discuss the following terms. i. slectivity ii. hydrophillic sol iii. peptization. 3
22. An organic compound (A) C5H11 Br on treatment with alcoholic caustic potash gives a hydrocarbon (B) C7H10. (B) on treatment with ozone and subsequent hydrolysis gives C and D.C does not give tollen’s reagent test ,both C&D gives idoform test. What are (A) ,(B),C and D. Explain reactions. 3
23. Prove that the time required for completion of ¾th of a first order reaction is twice the time required for the completion of half of the reaction. 3
24. What are : 3
(i) Inhibitors. (ii) Cataphoresis. (iii) Peptization.
25. A first order reaction takes 69.3 minutes for 50% completion. Set up an equation for determining the time required for 80% completion of this reaction. 3
26. What are biodegradable and non-biodegradable detergents? Give one example of each. 3
27. Answer the following: 3
(i) How do you classify carbohydrates on the basis of their hydrolysis?
(ii) What are nucleic acids? Mention their two important functions.
Section – D
28. a) State Henry’s law for solubility of a gas in a liquid. explain the significance of Henry’s law constant. At the same temperature , hydrogen is more soluble in water than helium. Which of them will have higher value of KH and why?
b) Explain elevation in boiling point of a solution with the help of vapour pressure temperature diagram.
OR
a) Why is a molar solution of solute in water is more concentrated than a molal solution?
b) Explain depression in freezing point of a solution on the addition of a solute. Show that depression in freezing point is a colligative property. 5
29. (a) What are primary and secondary cells? Discuss Variation of molar conductivity with dilution. 4
(b) What is abnormal molecular mass? 1
OR
(a) What kind of complex should be formed in dry cell by NH3. 5
(b) How the corrosion is an electrochemical process ? give the reaction.
(c) During the silver plating on a metal plate having area 10 cm2 in an electrolytic cell 15 A current is passed for one hour.What will be the thickness of silver plating if density of silver metal is 10.8 g/cm3 .
30. Write chemical equations(only) for the following reactions : 5
(a) (i) Etard reaction
(ii) Cannizzaro's reaction
(iii) Aldol condensation
(b) Of aldehydes and ketones which would reduce Tollen's reagent ? Why
OR
(a) How will you prepare the following compounds from benzene ? you may use any inorganic reagent and any organic reagent having not more than one carbon atom.
(i) p-nitrobenzaldehyde
(ii) Methyl benzoate
(iii) Phenylacetic acid
(b) Explain why carboxylic acids do not give reactions of aldehydes and ketones.