12th Chemistry Paper Solutions Set 1 : CBSE Delhi Previous Year 2012

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 :

What is meant by “doping”™ in a semiconductor?


Answer :

Doping is the process of increasing the conductivities of the intrinsic semiconductors by adding suitable impurity.

Q2 :

What is the role of graphite in the electrometallurgy of aluminium?


Answer :

In the metallurgy of aluminium, steel cathode and graphite anode are used. The graphite anode is useful for the reduction of Al2O3 into Al.

Q3 :

Which one of is not likely to exist and why?


Answer :

is not likely to exist because the oxidation state of P is +3 here, which is less stable.

Q4 :

Give the IUPAC name of the following compound.


Answer :

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Q5 :

Draw the structural formula of 2-methylpropan-2-ol molecule.


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Q6 :

Arrange the following compounds in an increasing order of their reactivity in nucleophilic addition reactions: ethanol, propanal, propanone, butanone.


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Q7 :

Arrange the following in the decreasing order of their basic strength in aqueous solutions:

CH3NH2, (CH3)2NH, (CH3)3 N and NH3


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Q8 :

Define the term, “homopolymerisation”™ giving an example.


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Q9 :

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°C. Determine the van”™t Hoff factor for trichloroacetic acid. (Kb for water = 0.512 kg mol−1)

OR

Define the following terms:

(i) Mole fraction

(ii) Isotonic solutions

(iii) Van”™t Hoff factor

(iv) Ideal solution


Answer :

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Q10 :

What do you understand by the “order of a reaction”™? Identify the reaction order from each of the following units of reaction rate constant:

(i) L−1 mol s−1

(ii) L mol−1 s−1


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Q11 :

Name the two groups into which phenomenon of catalysis can be divided. Give an example of each group with the chemical equation involved.


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Q12 :

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


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Q13 :

Describe the principle involved in each of the following processes.

(i) Mond process for refining of Nickel.

(ii) Column chromatography for purification of rare elements.


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Q14 :

Explain the following giving an appropriate reason in each case.

(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.


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Q15 :

Complete the following chemical equations:

(i)

(ii)


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Q16 :

What is meant by (i) peptide linkage (ii) biocatalysts?


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Q17 :

Write any two reactions of glucose which cannot be explained by the open chain structure of glucose molecule.


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Q18 :

Draw the structure of the monomer for each of the following polymers:

(i) Nylon 6

(ii) Polypropene


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Q19 :

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?

OR

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


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Q20 :

Calculate the amount of KCl which must be added to 1 kg of water so that the freezing point is depressed by 2K. (Kf for water = 1.86 K kg mol−1)


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Q21 :

For the reaction

2NO(g) + Cl2(g) → 2 NOCl(g)

The following data were collected. All the measurements were taken at 263 K:

Experiment No.

Initial [NO] (M)

Initial [Cl2] (M)

Initial rate of disappearance of Cl2 (M/min)

1

0.15

0.15

0.60

2

0.15

0.30

1.20

3

0.30

0.15

2.40

4

0.25

0.25

?

(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?


Answer :

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Q22 :

How would you account for the following?

(i) Many of the transition elements are known to form interstitial compounds.

(ii)The metallic radii of the third (5d) series of transition metals are virtually the same as those of the corresponding group member of the second (4d) series.

(iii)Lanthanoids from primarily +3 ions, while the actinoids usually have higher oxidation states in their compounds, +4 or even + 6 being typical.


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Q23 :

Give the formula of each of the following coordination entities:

(i) Co3+ ion is bound to one Cl, one NH3 molecule and two bidentate ethylene diamine (en) molecules.

(ii) Ni2+ ion is bound to two water molecules and two oxalate ions.

Write the name and magnetic behaviour of each of the above coordination entities.

(At. nos. Co = 27, Ni = 28)


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Q24 :

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


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Q25 :

Draw the structure and name the product formed if the following alcohols are oxidized. Assume that an excess of oxidizing agent is used.

(i) CH3CH2CH2CH2OH

(ii) 2-butenol

(iii) 2-methyl-1-proponal


Answer :

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Q26 :

Write chemical equation for the following conversions:

(i) Nitrobenzene to benzoic acid.

(ii) Benzyl chloride to 2-phenylethanamine.

(iii) Aniline to benzyl alcohol.


Answer :

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Q27 :

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

(i) Tranquilizers

(ii) Food preservatives

(iii) Synthetic detergents


Answer :

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Q28 :

(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

Determine E° and ΔG° for the reaction

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 0.001 M KCl solution at 298 K is 1500Ω. What is the cell constant if the conductivity of 0.001 M KCl solution at 298 K is 0.146 x 10-3S cm-1?


Answer :

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Q29 :

(a) Complete the following chemical reactions equations:

(i)

(ii)

(b) Predict the shape and the asked angle (90° or more or less) in each of the following cases:

(i) and the angle O - S - O

(ii) ClF3 and the angle F - Cl - F

(iii) XeF2 and the angle F - Xe - F

OR

(a) Complete the following chemical equations:

(i)

(ii)

(b) Draw the structures of the following molecules:

(i) H3PO2

(ii) H2S2O7

(iii) XeOF4


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Q30 :

(a) Illustrate the following name reaction giving suitable example in each case:

(i) Clemmensen reduction

(ii) Hell-Volhard-Zelinsky reaction

(b) How are the following conversions carried out?

(i) Ethylcyanide to ethanoic acid

(ii) Butan-1-ol to butanoic acid

(iii) Benzoic acid to m-bromobenzoic acid

OR

(a) Illustrate the following reactions giving a suitable example for each.

(i) Cross aldol condensation

(ii) Decarboxylation

(b) Give simple tests to distinguish between the following pairs of compounds

(i) Pentan-2-one and Pentan-3-one

(ii) Benzaldehyde and Acetophenone

(iii) Phenol and Benzoic acid


Answer :

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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.