CBSE Sample Paper
Subject – Chemistry
Class – 12th
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.
iii. Questions 9 to 18 are short answer type carrying 2 marks each.
iv. Questions 19 to 27 are also short answer type carrying 3 marks each.
v. Questions 28, 29 & 30 are long answer type carrying 5 marks each.
vi. Calculators are not permitted. Use log tables if necessary.
1. Give The Methiod of Prep. of XeOF4 & XeO3 from XeF6.
2. Which point defect in crystals alter the density of the relevant solid?
3. Write the structural formula of 4-oxo pentanal.
4. Electrons are trapped in anionic vacancies.
5. N-atom is most electronegative and the bond pairs and lone pair are closest therefore there is strongrepulsion which leads to easy coordination of lone pair.
6. A chemical bond (in chemisorption) is always stronger than vander Waals forces ( in physisorption)
7. Why is glass considered a super cooled liquid?
8. Why does NO2 dimerise ?
9. Explain negative deviation of non-ideal solution with example ?
10. Write reactions of mercury cell at anode and cathode ?
11. (i) A solution having lower concentration hence osmotic pressure than a given solution.
(ii) Constant boiling mixtures from which further separation of solute and solvent is not possible.
12. (a) Those amino acids which cannot be synthesized in the body and hence must be given in the diet.
(b) Human stomach does not have enzymes to break cellulose molecule hence it cannot be digested.
13. A reaction is first order in A and second order in B.How is the rate of reaction be affected if the concentration of this reaction is
i)Doubled
ii)Reduced to half
14. i) Write the method of preparation of Phosphine gas from P4.
ii) How is O3 estimated quantitatively?
15. Explain the following :
a) Denaturation of protein.
b) Two strands of DNA are not identical but complimentary to each other. Explain this statement.
16. What is a biodegradable polymer? Write the monomer of Nylon 6 and Neoprene.
17. Explain the following with an application:
(i) Reaction of nitrous acid with aliphatic primary amine
(ii) Diazotization
18. In the electrolytic refining of copper name the common elements present in the anode mud. Why are they so present?
19. Draw The Structure of 1)H2SO5 2)H2S2O8 3)HOClO3 4) BrF3 5)XeF6.
20. (a) Why chloramphenicol is regarded as a broad spectrum antibiotic.
(b) Write one example each of anionic and cationic detergents.
21. Calculate the standard cell potential of galvanic cell in which the following reactions take place:
2 Cr (s) + 3 Cd2+ (aq) --------------> 2 Cr3+ (aq) + 3 Cd (aq).
Calculate the Gibb’s energy change and the equilibrium constant for the reaction.
E0 Cr3+/Cr = - 0.74 V, E0 Cd2+/Cd =-0.40 V
22. (i) What is electrokinetic potential?
(ii) Why is FeCl3 solution used to stop bleeding?
(iii) What is the role of MnO2 in the decomposition of Hydrogen peroxide?
23. Henry’s law constant for CO2 in water is 1.67x108 Pa at 298 K. Calculate the quantity of CO2 in 500 mL of soda water when packed under 2.5 atm CO2 pressure at 298 K.
24. (i) What are emulsions? What are their different types? Give example of each type.
(ii) What is demulsification? Name two demulsifiers..?
(iii) Action of soap is due to emulsification and micelle formation. Comment
25. What happens when D-glucose is treated with the following reagents?
(i) HI (ii) Bromine water (iii) HNO3.
26. (i) Inhibitors or catalytic poisons are those substances which decrease the activity of a catalyst.
(ii) Cataphoresis is the movement of colloidal particles towards either of the electrodes under the influence of an electric field.
(iii) The conversion of a freshly precipitated substance into colloidal state by the addition of a suitableelectrolyte is called peptization.
27. (a) Antipyretic as well as analgesic.
(b) (i) As an antiseptics in soaps.
(ii) As an antioxidant.
28. (a) How do you convert the following?
(i) Benzaldehyde to α –hydroxy phenyl ethanoic acid
(ii) Ethanol to to 1,3 di- hydroxy butane
(b) Account for the following:
(i) Carboxyl group attached to aryl & vinyl carbon increases acidic strength.
(ii) pKa of chloro acetic acid is higher than acetic acid.
(iii) Methanal is the most reactive carbonyl compound towards nucleophiles.
29. (a) Give simple chemical tests to distinguish betweenPropanal and Propanone
(b) Cyclohexanone forms cyanohydrin in good yield but 2,2,6-trimethylcyclohexanonedoes not?
(c) An organic compound with the molecular formula 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.
30. (a) At anode : 2H2(g) + 4OH- → 4H2O(l) + 4e-
At cathode: O2(g) + 2H2O(l) + 4e- → 4OH-.
(b) (i) The limiting molar conductivity of an electrolyte, i.e.molar conductivity at infinite dilution, is the sum of the limiting ionic conductivities of the cation and the anion each multiplied with the no. of ions present in the one formula unit of the electrolyte.
e.g. Λom for AxBy = x lo (A) y+ + y lo (B) x-
(ii) H+ ions are required for rusting. Alkaline medium will combine with H+ ions and inhibit rusting.