CBSE Question Paper 2012 class 12 Chemistry

General Instructions

1. All questions are compulsory.
2. Marks for each question are indicated against it.
3. Question numbers 1 to 8 are very short-answer questions, carrying 1 mark each. Answer these in one word or about one sentence each.
4. Question numbers 9 to 18 are short-answer questions, carrying 2 marks each. Answer these in about 30 words each.
5. Question numbers 19 to 27 are short-answer questions of 3 marks each. Answer these in about 40 words each.
6. Question numbers 28 to 30 are long-answer questions of 5 marks each. Answer these in about 70 words each.
7. Use Log Tables, if necessary Use of calculators is not permitted.

CHEMISTRY 2012 (Delhi)

1. Write a point of distinction between a metallic solid and an ionic solid other than metallic lustre. [1]

2. Which one of PCl₄⁺ and PCl₄^– is not likely to exist and why? [1]

3. What is the role of graphite in the electrometallurgy of aluminium? [1]

4. Arrange the following compounds in an increasing order of their reactivity in nucleophilic addition reactions: ethanal, propanal, propanone, butanone. [1]

5. Draw the structural formula of 2-methylpropan-2-ol molecule. [1]

6. Give the IUPAC name of the following compound. [1]

7. Define the term, “homopolymerisation giving an example. [1]

8. Arrange the following in the decreasing order of their basic strength in aqueous solutions: CH₃NH₂, (CH₃)₂NH,(CH₃)₃N and NH₃[1]

9. A 1.00 molal aqueous solution of trichloroacetic acid (CCl₃COOH) is heated to its boiling point. The solution has the boiling point of 100.18^oC. Determine the vant Hoff factor for trichloroacetic acid. (K_b for water = 0.512K kg mol^-1) [2]

OR

Define the following terms:
(i) Mole fraction
(ii) Isotonic solutions
(iii) Van ‘t Hoff factor
(iv) Ideal solution

10. What do you understand by the “order of a reaction? Identify the reaction order from each of the following units of reaction rate constant: [2]
i) L^-1 mols^-1
ii) L mol^-1s^-1

11. Describe a conspicuous change observed when [2]
(i) a solution of NaCl is added to a sol of hydrated ferric oxide.
(ii) a beam of light is passed through a solution of NaCl and then through a sol.

12. What is meant by coagulation of a colloidal solution? Describe briefly any three methods by which coagulation of lyophobic sols can be carried out. [2]

13. Describe the following: [2]
(i) The role of cryolite in electro metallurgy of aluminium.
(ii) The role of carbon monoxide in the refining of crude nickel.

14. What is meant by (i) peptide linkage (ii) biocatalysts? [2]

15. Explain the following giving an appropriate reason in each case. [2]
(i) O₂ and F₂ both stabilize higher oxidation states of metals but O₂ exceeds F₂ in doing so.
(ii) Structures of Xenon fluorides cannot be explained by Valence Bond approach.

16. Complete the following chemical equations: [2]

17. Draw the structure of the monomer for each of the following polymers: [2]
(i) Nylon 6
(ii) Polypropene

18. Write the main structural difference between DNA and RNA. Of the two bases, thymine and uracil, which one is present in DNA? [2]

19. Tungsten crystallizes in body centred cubic unit cell. If the edge of the unit cell is 316.5 pm, what is the radius of tungsten atom? [3]

OR

Iron has a body centred cubic unit cell with a cell dimension of 286.65pm. The density of iron is 7.874g cm^-3.Use this information to calculate Avogadro’s number. (At mass of Fe=55.845u)

20. A solution of glycerol (C₃H₈O₃) in water was prepared by dissolving some glycerol in 500g of water. This solution has a boiling point of 100.42^oC while pure water boils at 100 °C. What mass of glycerol was dissolved to make the solution?(K_b for water = 0.512K kg mol^-1) [3]

21. For the reaction [3]
the following data were collected. All the measurements were taken at 263 K:

(a) Write the expression for rate law.
(b) Calculate the value of rate constant and specify its units.
(c) What is the initial rate of disappearance of Cl₂ in exp. 4?

22. State a reason for each of the following situations: [3]
(i) Co²⁺ is easily oxidized to Co³⁺ in presence of a strong ligand.
(ii) CO is a stronger complexing reagent than NH_3.
(iii) The molecular shape of Ni(CO)₄ is not the same as that of [Ni(CN)₄]^2-.

23. How would you account for the following? [3]
(i) With the same d-orbital configuration (d⁴) Cr²⁺ is a reducing agent while Mn³⁺ is an oxidizing agent.
(ii) The actinoids exhibit a larger number of oxidation states than the corresponding members in the lanthanoid series.
(iii) Most of the transition metal ions exhibit characteristic in colours in aqueous solutions.

24. Write chemical equations for the following conversions: [3]
(i) Nitrobenzene to benzoic acid.
(ii) Benzyl chloride to 2-phenylethanamine.
(iii) Aniline to benzyl alcohol.

25. What are the following substances? Give one example of each one of them. [3]
(i) Tranquilizers
(ii) Food preservatives
(iii) Synthetic detergents

26. Draw the structure and name the product formed if the following alcohols are oxidized. Assume that an excess of oxidizing agent is used. [3]
(i) CH₃CH₂CH₂CH₂OH
(ii) 2-butenol
(iii) 2-methyl-1-propanol

27. Although chlorine is an electron withdrawing group, yet it is ortho-, para-directing in electrophilic aromatic substitution reactions. Explain why it is so? [3]

28. (a) Complete the following chemical reaction equations: [5]

(b) Predict the shape and the asked angle ( or more or less) in each of the following cases:

OR

(a) Complete the following chemical equations:

(b) Draw the structures of the following molecules:

29. (a) What type of a battery is the lead storage battery? Write the anode and the cathode reactions and the overall reaction occurring in a lead storage battery when current is drawn from it.
(b) In the button cell, widely used in watches, the following reaction takes place
Zn(s) + Ag₂O(s)+ H₂O(l)→→Zn²⁺(aq)+2Ag(s)+2OH^–(aq)
Determine E^o and △△G⁰ from the reaction.(given: E^o_Ag+/Ag = +0.80V, E²⁺_Zn2+/Zn = -0.76V) [5]

OR

(a) Define molar conductivity of a solution and explain how molar conductivity changes with change in concentration of solution for a weak and a strong electrolyte.
(b) The resistance of a conductivity cell containing 0.001M KCl solution at 298K is 1500 ππ  What is the cell constant if the conductivity of 0.001M KCl solution at 298 K is 0.146×10^-3 S cm^-1?

30. (a)Give a plausible explanation for each one of the following: [5]
(i) There are two -NH₂ groups in semicarbazide. However, only one such group is involved in the formation of semicarbazones.
(ii) Cyclohexanone forms cyanohydrin in good yield but 2, 4, 6-trimethylcyclohexanone does not.
(b) An organic compound with molecular formula C₉H₁₀O forms 2, 4, – DNP derivative, reduces Tollens reagent and undergoes Cannizzaro’s reaction. On vigorous oxidation it gives 1, 2-benzene-di-carboxylic acid. Identify the compound.

OR

(a) Give chemical tests to distinguish between
(i) Phenol and Benzoic acid
(ii) Benzophenone and Acetophenone
(b) Write the structures of the main products of following reactions:

Chemistry Question Paper 2012

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