12th Chemistry Paper Solutions Set 3 : CBSE All India 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 :

Define “activation energy”™ of a reaction.


Answer :

The energy required to form an activated complex in any reaction, is known as activation energy of that reaction.

Q2 :

What is meant by “reverse osmosis”™?


Answer :

The phenomenon of reversal of the direction of osmosis by the application of a pressure larger than the osmotic pressure on the solution side is known as reverse osmosis. In this case, the pure solvent flows out of the solution through a semi permeable membrane.

Q3 :

What type of ores can be concentrated by magnetic separation method?


Answer :

If the ore or the gangue can be attracted by the magnetic field, then the ore can be concentrated by the process of magnetic separation.

Q4 :

Write the IUPAC name of the following compound: CH2 = CHCH2Br


Answer :

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Q5 :

What is meant by “lanthanoid contraction”™?


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Q6 :

How would you convert ethanol to ethene?


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Q7 :

Draw the structure of 4-chloropentan-2-one.


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Q8 :

Give a chemical test to distinguish between ethylamine and aniline.


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Q9 :

Calculate the packing efficiency of a metal crystal for a simple cubic lattice.


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Q10 :

Explain how you can determine the atomic mass of an unknown metal if you know its mass density and the dimensions of unit cell of its crystal.


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Q11 :

Differentiate between molarity and molality values for a solution. What is the effect of change in temperature on molarity and molality values?


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Q12 :

The thermal decomposition of HCO2H is a first order reaction with a rate constant of 2.4 × 10−3 s−1 at a certain temperature. Calculate how long will it take for three-fourths of initial quantity of HCO2H to decompose.

(log 0.25 = − 0.6021)


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Q13 :

What do you understand by the rate law and rate constant of a reaction?

Identify the order of a reaction if the units of its rate constant are:

(i) L−1 mol s−1

(ii) L mol−1 s−1


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Q14 :

Describe the principle controlling each of the following processes:

(i) Preparation of cast iron form pig iron.

(ii) Preparation of pure alumina (Al2O3) from bauxite ore.


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Q15 :

Explain giving reasons:

(i) Transition metals and their compounds generally exhibit a paramagnetic behaviour.

(ii) The chemistry of actinoids is not so smooth as that of lanthanoids.


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Q16 :

Complete the following chemical equations:

(i)

(ii)

OR

State reasons for the following:

(i) Cu (I) ion is not stable in an aqueous solution.

(ii) Unlike Cr3+, Mn2+, Fe3+ and the subsequent other M2+ ions of the 3d series of elements, the 4d and the 5d series metals generally do not form stable cationic species.


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Q17 :

Write the main structural difference between DNA and RNA. Of the four bases, name those which are common to both DNA and RNA.


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Q18 :

Write such reactions and facts about glucose which cannot be explained by its open chain structure.


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Q19 :

A solution prepared by dissolving 8.95 mg of a gene fragment in 35.0 mL of water has an osmotic pressure of 0.335 torr at 25°C.

Assuming that the gene fragment is a non-electrolyte, calculate its molar mass.


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Q20 :

Classify colloids where the dispersion medium is water. State their characteristics and write an example of each of these classes.

OR

Explain what is observed when

(i) an electric current is passed through a sol

(ii) a beam of light is passed through a sol

(iii) an electrolyte (say NaCl) is added to ferric hydroxide sol


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Q21 :

How would you account for the following:

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

(ii) The acidic strength of compounds increases in the order:

PH3 < H2S < HCl

(iii) SF6 is kinetically inert.


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Q22 :

Write the state of hybridization, the shape and the magnetic behaviour of the following complex entities:

(i) [Cr(NH3)4 Cl2] Cl

(ii) [Co(en)3] Cl3

(iii) K2 [Ni(CN)4]


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Q23 :

State reasons for the following:

(i) pKb value for aniline is more than that for methylamine.

(ii) Ethylamine is soluble in water whereas aniline is not soluble in water.

(iii) Primary amines have higher boiling points than tertiary amines.


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Q24 :

Rearrange the compounds of each of the following sets in order of reactivity towards SN2 displacement:

(i) 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane

(ii) 1-Bromo-3-methylbutane, 2-Bromo-2-methylbutane, 3-Bromo-2-methylbutane

(iii) 1-Bromobutane, 1-Bromo-2, 2-dimethylpropane, 1-Bromo-2-methylbutane


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Q25 :

How would you obtain the following:

(i) Benzoquinone from phenol

(ii) 2-methyl propan-2-ol from methyl-magnesium bromide

(iii) Propane-2-ol from propene


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Q26 :

Write the names and structures of the monomers of the following polymers:

(i) Buna-S

(ii) Dacron

(iii) Neoprene


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Q27 :

What are the following substances? Give one example of each.

(i) Food preservatives

(ii) Synthetic detergents

(iii) Antacids


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Q28 :

(a) Draw the structures of the following molecules:

(i) (HPO3)3

(ii) BrF3

(b) Complete the following chemical equations:

(i) HgCl2 + PH3

(ii) SO3 + H2SO4

(iii) XeF4 + H2O →

OR

(a) What happens when

(i) chlorine gas is passed through a hot concentrated solution of NaOH?

(ii) sulphur dioxide gas is passed through an aqueous solution of a Fe (III) salt?

(b) Answer the following:

(i) What is the basicity of H3PO3 and why?

(ii) Why does fluorine not play the role of a central atom in inter-halogen compounds?

(iii) Why do noble gases have very low boiling points?


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Q29 :

(a) What type of a battery is lead storage battery? Write the anode and cathode reactions and the overall cell reaction occurring in the operation of a lead storage battery.

(b) Calculate the potential for half-cell containing 0.10 M K2Cr2O7 (aq), 0.20 M Cr3+ (aq) and 1.0 x 10-4 M H+ (aq)

The half-cell reaction is and the standard electrode potential is given as E0 = 1.33 V.

OR

(a) How many moles of mercury will be produced by electrolysing 1.0 M

Hg (NO3)2 solution with a current of 2.00 A for 3 hours?

[Hg(NO3)2 = 200.6 g mol-1]

(b) A voltaic cell is set up at 25°C with the following half-cells Al3+ (0.001 M) and Ni2+ (0.50 M). Write an equation for the reaction that occurs when the cell generates an electric current and determine the cell potential.


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Q30 :

(a) Illustrate the following name reactions:

(i) Cannizzaro’s reaction

(ii) Clemmensen reduction

(b) How would you obtain the following:

(i) But-2-enal from ethanal

(ii) Butanoic acid from butanol

(iii) Benzoic acid from ethylbenzene

OR

(a) Given chemical tests to distinguish between the following:

(i) Benzoic acid and ethyl benzoate

(ii) Benzaldehyde and acetophenone

(b) Complete each synthesis by giving missing reagents or products in the following:

(i)

(ii)

(iii)


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12th Chemistry Paper Solutions Set 3 : CBSE Delhi Previous Year 2013 will be available online in PDF book soon. The solutions are absolutely Free. Soon you will be able to download the solutions.