12th Chemistry Paper Solutions Set 3 : CBSE Delhi Previous Year 2011

General Instructions:
(i) All questions are compulsory
(ii) Question numbers 1 to 8 are very short-answer questions and carry 1 mark each.
(iii) Question numbers 9 to 18 are short-answer questions and carry 2 marks each.
(iv) Question numbers 19 to 27 are also short-answer questions and carry 3 marks.
(v) Question numbers 28 to 30 are long-answer questions and carry 5 marks each.
(vi) Use Log Tables, if necessary. Use of calculators is not allowed.
Q1 :

Crystalline solids are anisotropic in nature”™. What does this statement mean?


Answer :

This statement means that some of the physical properties of crystalline solids such as electrical resistance or refractive index show different values when measured along different directions in the same crystals.

Q2 :

Express the relation among the conductivity of solution in the cell, the cell constant and the resistance of solution in the cell.


Answer :

The conductivity of a solution, the cell constant and the resistance of a cell are related by the following expression.

Q3 :

Define “shape-selective catalysis”™.


Answer :

A catalytic reaction which depends upon the pore structure of the catalyst and on the size of the reactant and the product molecules is called shape-selective catalysis.

For example, catalysis by zeolites is a shape-selective catalysis. The pore size present in the zeolites ranges from 260-740 pm. Thus, molecules having a pore size more than this cannot enter the zeolite and undergo the reaction.

Q4 :

Draw the structure of BrF3 molecule.


Answer :

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Q5 :

Arrange the following compounds in an increasing order of their solubility in water: 

C6H5NH2, (C2H5)2NH, C2H5NH2


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Q6 :

Write the IUPAC name of the following compound: 

(CH3)3 CCH2Br 


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Q7 :

Draw the structure of 3-methylbutanal.


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Q8 :

In nylon 6, 6 what does the designation “6, 6”™ mean?


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Q9 :

What type of a battery is lead storage battery? Write the anode and the cathode reactions and the overall reactions occurring in a lead storage battery.

 


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Q10 :

Two half-reactions of an electrochemical cell are given below:

Construct the redox equation from the standard potential of the cell and predict it the reaction is reactant favoured or product favoured.


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Q11 :

State reasons for each of the following: 

(i) The N - O bond in is shorter than the N - O bond in

(ii) SF6 is kinetically an inert substance. 

OR

State reasons for each of the following: 

(i) All the P-Cl bonds in PCl5 molecule are not equivalent. 

(ii) Sulphur has greater tendency for catenation than oxygen.


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Q12 :

Distinguish between “rate expression”™ and “rate constant”™ of a reaction.


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Q13 :

Assign reasons for each of the following: 

(i) Transition metals generally form coloured compounds. 

(ii) Manganese exhibits the highest oxidation state of +7 among the 3d series of transition elements. 


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Q14 :

How would you obtain 

(i) Picric acid (2, 4, 6-trinitrophenol) from phenol, 

(ii) 2-Methylpropene from 2-methylpropanol?


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Q15 :

Explain the following giving one example for each:

(i)Reimer-Tiemann reaction.

(ii)Friedel Craft”™s acetylation of anisole.


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Q16 :

Describe what you understand by primary structure and secondary structure of proteins.


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Q17 :

What is essentially the difference between α-form of glucose and β-form of glucose? Explain.


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Q18 :

Name the sub-groups into which polymers are classified on the basis of magnitude of intermolecular forces.


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Q19 :

The density of lead is 11.35 g cm−3 and the metal crystallizes with fcc unit cell. Estimate the radius of lead atom (At. Mass of lead = 207 g mol−1 and NA = 6.02 × 1023 mol−1


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Q20 :

Explain how the phenomenon of adsorption finds application in each of the following processes:

(i) Production of vacuum

(ii) Heterogeneous catalysis

(iii) Froth Floatation process

OR

Define each of the following terms:

(i) Micelles

(ii) Peptization

(iii)Desorption


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Q21 :

Nitrogen pentoxide decomposes according to equation: 2N2O5(g) 4NO2(g) + O2(g) 

This first order reaction was allowed to proceed at 40° C and the data below were collected:

[N2O5] (M) Time (min)
0.400 0.00
0.289 20.0
0.209 40.0
0.151 60.0
0.109 80.0

(a) Calculate the rate constant. Include units with your answer. 

(b) What will be the concentration of N2O5 after 100 minutes? 

(c) Calculate the initial rate of reaction.


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Q22 :

Complete the following chemical equations:

(i)

(ii)

(iii)


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Q23 :

Write the name, stereochemistry and magnetic behaviour of the following: 

(At. nos. Mn = 25, Co = 27, Ni = 28) 

(i) K4[Mn(CN)6

(ii) [Co(NH3)5Cl]Cl2

(iii) K2[Ni(CN)4]


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Q24 :

Describe the principle behind each of the following processes:

(i)Vapour phase refining of a metal.

(ii)Electrolytic refining of a metal.

(iii)Recovery of silver after silver ore was leached with NaCN.


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Q25 :

Answer the following: 

(i) Haloalkanes easily dissolve in organic solvents, why? 

(ii) What is known as a racemic mixture? Give an example. 

(iii) Of the two bromoderivatives, C6H5CH(CH3)Br and C6H5CH(C6H5)Br, which one is more reactive in substitution reaction and why?


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Q26 :

Complete the following chemical equations: 

(i)

(ii) C6H5N2Cl + H3PO2 + H2O

(iii) 


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Q27 :

Answer the following questions: 

(i) Why do soaps not work in hard water? 

(ii) What are the main constituents of dettol? 

(iii) How do antiseptics differ from disinfectants?


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Q28 :

(a) Give chemical tests to distinguish between 

(i) Propanal and propanone, 

(ii) Benzaldehyde and acetophenone. 

(b) How would you obtain 

(i) But-2-enal from ethanal, 

(ii) Butanoic acid from butanol, 

(iii) Benzoic acid from ethylbenzene? 

OR

(a) Describe the following giving linked chemical equations: 

(i) Cannizzaro reaction 

(ii) Decarboxylation 

(b) Complete the following chemical equations: 

(i)

(ii)

(iii)


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Q29 :

(a) Explain the following: 

(i) NF3 is an exothermic compound whereas NCl3 is not. 

(ii) F2 is most reactive of all the four common halogens. 

(b) Complete the following chemical equations: 

(i) C + H2SO4 (conc)

(ii) P4 + NaOH + H2O

(iii)

OR

(a) Account for the following: 

(i) The acidic strength decreases in the order HCl > H2S > PH3

(ii) Tendency to form pentahalides decreases down the group in group 15 of the periodic table. 

(b) Complete the following chemical equations: 

(i) P4 + SO2Cl2

(ii) XeF2 + H2O

(iii)


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Q30 :

(a) Differentiate between molarity and molality for a solution. How does a change in temperature influence their values? 

(b) Calculate the freezing point of an aqueous solution containing 10.50 g of MgBr2 in 200 g of water. (Molar mass of MgBr2 = 184 g) (Kf for water = 1.86 K kg mol−1

OR

(a) Define the terms osmosis and osmotic pressure. Is the osmotic pressure of a solution a colligative property? Explain. 

(b) Calculate the boiling point of a solution prepared by adding 15.00 g of NaCl to 250.0 g of water. (Kb for water = 0.512 K kg mol−1), (Molar mass of NaCl = 58.44 g)


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