CBSE Board Class 12 Chemistry Previous Year Question Papers 2007

previous year  paper-2007
class-12

chemistry

All questions are compulsory.

Marks for each question are indicated against it.

Question number 1 to 5 are very short–answer questions, carrying 1 mark each Answer these in one word or about one sentence each.

Question number 6 to 12 are short-answer  questions, carrying 2 marks each. Answer these in about 30 words each.

Question number 13 to 24 are short-answer questions of 3 marks each. Answer these in about 40 words each.

Question number 25 to 27 are long-answer questions of 5 marks each. Answer these in about 70 words each.

Use Log Tables, if necessary. Use of calculators is not permitte



Question 1: Find out the number of atoms per unit cell in a face-centred cubic structure having only single atoms at its lattice points.


Question 2: State the condition resulting in reverse osmosis.


Question 3: Express the rate of the following reaction in terms of disappearance of hydrogen in the reaction

3 H2(g)+N2(g) ->2NH3(g)      


Question 4: Name the following compound according to IUPAC system:

CH3COCH2COCH3  


Question 5: Why do amines react as nucleophiles?   


Question 6:
(a) Write the mathematical expression for the relationship of wavelength () of a moving particle and its momentum(p)

(b) What physical meaning is attributed to the square of the absolute value of wave function, |Ψ|^2  


Question 7: State the Heisenberg Uncertainty Principle and explain as to why it is not of real consequence when applied to a macroscopic object, like a cricket ball. 


Question 8: Define conductivity and molar conductivity for the solution of an electrolyte.  


Question 9: How would you account for the following:

(i)  Sulphur hexafluoride is less reactive than sulphur tetrafluoride.

(ii) Of the noble gases only xenon forms known chemical compounds. 


Question 10: On the basis of the standard electrode potential values stated for acid solution, predict whether Ti4+ species may be used to oxidise FeII to FeIII.

Reaction E /V

TiIV +e-  ->Ti3+  : +0.01

Fe3 +e- ->Fe2  : +0.77   


Question 11: What are chiral objects? Indicate the presence of center of chirality, if any, in the molecules of 3-bromopent -1-ene.  


Question 12: How many the following conversions be carried out:

(i)   Propene to propan-2-ol

(ii)  Anisole to phenol

(Write the reaction only) 


Question 13: Write formulae of the monomers of polythene and teflon. 


Question 14: Define bond order in a diatomic molecule. Find the bond order in O2 molecule. State and explain magnetic character of molecular oxygen.  


Question 15: Assign reasons for the following : Phosphorus doped silicon is a semiconductor. Schottky defect lowers the density of a solid. Some of the very old glass objects appear slightly milky instead of being transparent.  


Question 16: A 0.1539 molal aqueous solution of cane sugar (mol.mass=342 g mol-1) has a freezing point of 271 K while the freezing point of pure water is 273.15 K. What will be the freezing point of an aqueous solution containing 5 g of glucose (mol.mas=180g mol-1) per 100 g of solution? 


Question 17: Calculate the standard cell potential of the galvanic cell in which the following reaction takes place:

2 Cr(s)+3Cd2+(aq.) ->2Cr3+(aq.)+3Cd(s)

Also calculate the  rG value of the reaction.

(Given : Ecr3+/cr=+0.74V;E cd2+/cd=-0.40V and F=96500 C mol-1) 


Question 18: The rate constant for a first order reaction is 60s-1. How much time will it take to reduce the concentration of the reactant to 1/10th of its initial value?  


Question 19: Describe the following types of colloids, giving an example for each:

(i)   Multimolecular colloids

(ii)  Macromolecular colloids        


Question 20-: Explain the following terms with a suitable example in each case: 

Shape-selective catalysis  Dialysis


Question 21: How would you account for the following : The transition elements have high enthalpies of atomisation.

The transition metals and their compounds are found to be good catalysts in many processes.    


Question 22: Describe for any two of the following complex ions, the type of hybridization, shape and magnetic property:

[Fe(H2O6)]2+

[Co(NH3)6]3+

[NiCl4]2-

(At. Nos. Fe=26, Co=27, Ni=28)  


Question 23:  Complete the following statements for nuclear reactions:

(_94^239)Pu(a," β _) …………….

………………..(a,2n)(_85^211)At

(_966^246)Cm+ (_6^12)C ->………………+4(_0^1)n

(Note: You may use ‘X’ as symbol if the correct symbol in a reaction is not known)


Question 24: Write one chemical equation for each, to illustrate the following reactions:

Rosenmund reduction

Cannizzaro reaction

Fischer esterification    


Question 25: Account for any two of the following :

Amines are basic substances while amides are neutral.

Nitro compounds have higher boiling points than the hydrocarbons having almost the same molecular mass.

Aromatic amines are weaker bases than aliphatic amines. 



Question 26:
(a) Describe and illustrate with an example each, a mordant dye and a detergent,

(b)  Give an example of a liquid.propellant.  


Question 27:
(a) Prove that  Gsystem =-TStotal for a system which is not isolated.

(b)  The decomposition of Fe2O3 is a non-spontaneous process

2Fe2O3(S)->4 Fe(s)+3O2 (g), rG =+1487 KJ mol-1

Show that the reduction of Fe2O3 by CO can be made spontaneous by coupling with the following reaction.

2CO(g) +O2(g) -> 2CO2(g), rG=-514 kJ mol-1 


Question 28:
(a) Define the following terms:

Entropy

A spontaneous process

(b)  Given below are the standard Gibbs energy changes for two reaction at 1773 K:

C+O2 =CO2 :      rG = 380 kJ mol-1

2C+O2 2CO : rG =500 kJ mol-1

Discuss the possibility of reducing A12O3 with carbon at this temperature. Given that :

4Al+3O2 =2Al2O3 :rG =22500kJ mol-1         


Question 29 :
(a) Assign reasons for the following:

PbO2 is a stronger oxidising agent than SnO2.

In solid state PCl5 behaves as an ionic species,

Aluminium chloride (AlCl3) is very often used as a catalyst.

(b)  What is the structural difference between orthosilicates and pyrosilicates?      


Question 30:
(a) Assign reasons for the following :

The acid strengths of acids increase in the order

HF < HCl<HBr<HI

The lower oxidation state becomes more stable with increasing atomic number in Group 13.

H3PO2 behaves as a monoprotic acid.



(b)  Draw the structures of the following compounds:

(i)   SF4

(ii)  XeF2      


Question 31:
(a) Answer the following questions briefly:

What are reducing sugars?

What is meant by denaturation of a protein?

How is oxygen replenished in our atmosphere?

(b)  Define enzymes.



Question 32 : Answer the following questions briefly :

What are any two good sources of vitamin A?

What are nucleotides?

Give an example of simple lipids.

(b) How are carbohydrates classified?