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# Question Paper Solutions - Chemistry 2012 - 2013-CBSE 12th-Class 12 CBSE (Central Board of Secondary Education)

SubjectChemistry
Year2012 - 2013 (March)

Marks: 70
[1]1

How many atoms constitute one unit cell of a face-centered cubic crystal?

Chapter: [1] Solid State
Concept: Number of Atoms in a Unit Cell
[1]2

Name the method used for the refining of Nickel metal.

Chapter: [6] General Principles and Processes of Isolation of Elements
Concept: Refining
[1]3

What is the covalency of nitrogen in N2O5?

Chapter: [1] Solid State
Concept: Classification of Crystalline Solids
[1]4

Write the IUPAC name of

Chapter: [9] Coordination Compounds
Concept: Nomenclature of Coordination Compounds - Naming of Mononuclear Coordination Compounds
[1]5

What happens when CH3 − Br is treated with KCN?

Chapter: [10.02] Haloarenes
Concept: Chemical Reactions of Haloalkanes and Haloarenes - Reactions of Haloarenes - Nucleophilic Substitution
[1]6

Write the structure of 3-methyl butanal

Chapter: [12.01] Aldehydes and Ketones
Concept: Aldehydes and Ketones - Nomenclature
[1]7

Arrange the following in increasing order of their basic strength in aqueous solution:

CH3.NH2, (CH3)3N, (CH3)2NH

Chapter: [15] Cyanides, Isocyanides, Nitro compounds, Amines and Diazonium Salt
Concept: Amines - Chemical Reactions of Amines - Basic Character of Amines
[1]8

What are three types of RNA molecules which perform different functions?

Chapter: [14] Biomolecules
Concept: Introduction of Nucleic Acids
[2]9

8 g of glucose, C6H12O6 (Molar Mass = 180 g mol−1) is dissolved in 1 kg of water in a sauce pan. At what temperature will this solution boil?

(Kb for water = 0.52 K kg mol−1, boiling point of pure water = 373.15 K)

Chapter: [2] Solutions and Colligative Properties
Concept: Colligative Properties and Determination of Molar Mass - Elevation of Boiling Point
[2]10

The conductivity of 0.20 M solution of KCl at 298 K is 0.025 S cm−1. Calculate its molar conductivity.

Chapter: [6.04] Electrolytic conductance
Concept: Conductance of Electrolytic Solutions - Variation of Conductivity and Molar Conductivity with Concentration
[2]11
[2]11.1

Write the dispersed phase and dispersion medium of the following colloidal systems:

(i) Smoke

(ii) Milk

Chapter: [5] Surface Chemistry
Concept: Catalysis - Enzyme Catalysis
[2]11.2

What are lyophilic and lyophobic colloids ? Which of these sols can be easily coagulated on the addition of small amounts of electrolytes?

Chapter: [5] Surface Chemistry
Concept: Classification of Colloids - Classification Based on Nature of Interaction Between Dispersed Phase and Dispersion Medium
[2]12

Write the differences between physisorption and chemisorption with respect to the following:

(i) Specificity

(ii) Temperature dependence

(iii) Reversibility and

(iv) Enthalpy change

Chapter: [5] Surface Chemistry
[2]13

Which solution is used for the leaching of silver metal in the presence of air in the metallurgy of silver?

Chapter: [6] General Principles and Processes of Isolation of Elements
Concept: Oxidation Reduction

Out of C and CO, which is a better reducing agent at the lower temperature range in the blast furnace to extract iron from the oxide ore?

Chapter: [10] Chemistry of Transition and Inner-Transition Elements: d-Block: 3d, 4d and 5d series f-Block: 4f and 5f series
Concept: Occurrence of Metals
[2]14

What happens when

(i) PCl5 is heated ? Write the reactions involved.

Chapter: [7] P - Block Elements
Concept: P - Block Group 17 Elements - Chlorine

What happens when

H3PO3 is heated ?

Write the reactions involved.

Chapter: [7] P - Block Elements
Concept: P - Block Group 15 Elements - Phosphine
[2]15

Which metal in the first transition series (3d series) exhibits + 1 oxidation state most frequently and why?

Chapter: [8] "D" and "F" Block Elements
Concept: General Properties of the Transition Elements (D-block)

Which of the following cations are coloured in aqueous solutions and why ?

Sc3+, V3+, Ti4+, Mn2+ (At. Nos. Sc = 21, V = 23, Ti = 22, Mn = 25)

Chapter: [8] "D" and "F" Block Elements
Concept: General Properties of the Transition Elements (D-block)
[2]16

Chlorobenzene is extremely less reactive towards a nucleophilic substitution reaction. Give two reasons for the same.

Chapter: [10.02] Haloarenes
Concept: Chemical Reactions of Haloalkanes and Haloarenes - Reactions of Haloarenes - Nucleophilic Substitution
[2]17

Explain the mechanism of the following reaction:

Chapter: [11] Alcohols, Phenols and Ethers
Concept: Preparation of Ethers from Dehydration of Alcohols and Williamson Systhesis
[2]18

How will you convert: Propene to Propan-2-ol?

Chapter: [11] Alcohols, Phenols and Ethers
Concept: Preparation of Alcohols from Alkenes, Carbonyl Compounds and Grignard Reagents

How will you convert: Phenol to 2, 4, 6 − trinitrophenol?

Chapter: [11] Alcohols, Phenols and Ethers
Concept: Preparation of Alcohols from Alkenes, Carbonyl Compounds and Grignard Reagents
[3]19

What type of semiconductor is obtained when silicon is doped with boron?

Chapter: [19] Semiconductors
Concept: Electrical Properties - Applications of N-type and P-type Semiconductors

What type of magnetism is shown in the following alignment of magnetic moments?

Chapter: [2] States of Matters: Structure and Properties Solid State
Concept: Magnetic Properties

What type of point defect is produced when AgCl is doped with CdCl2?

Chapter: [1] Solid State
Concept: Imperfections in Solids - Introduction
[3]20

Determine the osmotic pressure of a solution prepared by dissolving 2.5 × 10−2 g of K2SO4 in 2L of water at 25°C, assuming that it is completely dissociated.

(R = 0.0821 L atm K−1 mol−1, Molar mass of K2SO4 = 174 g mol−1)

Chapter: [2] Solutions and Colligative Properties
Concept: Colligative Properties and Determination of Molar Mass - Osmosis and Osmotic Pressure
[3]21

Calculate the emf of the following cell at 298 K:

Fe(s)|Fe^(2+)(0.001M)||H^+(1M)|H_2 "(g)(1bar) ",Pt(s)

("Given " E_(cell)^@=+0.44V)

Chapter: [4] Electrochemistry
Concept: Galvanic Cells - Introduction
[3]22 | Attempt any one of the following
[3]22.1

How would you account for the following?

Transition metals exhibit variable oxidation states.

Chapter: [8] "D" and "F" Block Elements
Concept: General Properties of the Transition Elements (D-block)

How would you account for the following?

Zr (Z = 40) and Hf (Z = 72) have almost identical radii.

Chapter: [8] "D" and "F" Block Elements
Concept: General Properties of the Transition Elements (D-block)

How would you account for the following?

Transition metals and their compounds act as catalyst.

Chapter: [8] "D" and "F" Block Elements
Concept: General Properties of the Transition Elements (D-block)
[3]22.2

Complete the following chemical equations:

(i) Cr_2O_7^(2-)+6Fe^(2+)+14H^+ ->

(ii) 2CrO_4^(2-)+2H^+ ->

(iii) 2MnO_4^-+5C_2O_4^(2-)+16H^+ ->

Chapter: [8] "D" and "F" Block Elements
Concept: General Properties of the Transition Elements (D-block)
[3]23

Write the IUPAC names of the following coordination compounds: [Cr(NH3)3Cl3]

Chapter: [9] Coordination Compounds
Concept: Nomenclature of Coordination Compounds - Naming of Mononuclear Coordination Compounds

Write the IUPAC names of the following coordination compounds:  K3[Fe(CN)6]

Chapter: [9] Coordination Compounds
Concept: Nomenclature of Coordination Compounds - Naming of Mononuclear Coordination Compounds

Write the IUPAC names of the following coordination compounds:

[CoBr2(en)2]+, (en = ethylenediamine)

Chapter: [9] Coordination Compounds
Concept: Nomenclature of Coordination Compounds - Naming of Mononuclear Coordination Compounds
[3]24

Give the structures of A, B and C in the following reactions:

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Diazonium Salts - Chemical Reaction of Diazonium Salts - Reactions Involving Displacement of Nitrogen

Give the structures of A, B and C in the following reaction:

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Diazonium Salts - Chemical Reaction of Diazonium Salts - Reactions Involving Displacement of Nitrogen
[3]25
[1]25.1

Write the names and structure of the monomers of the following polymers: Buna − S

Chapter: [15] Polymers
Concept: Introduction of Polymers
[1]25.2

Write the names and structure of the monomers of the following polymers: Neoprene

Chapter: [15] Polymers
Concept: Introduction of Polymers
[1]25.3

Write the names and structure of the monomers of the following polymers: Nylon-6, 6

Chapter: [16] Polymers
Concept: Types of Polymerisation Reactions - Condensation Polymerisation Or Step Growth Polymerisation
[3]26

After watching a programme on TV about the adverse effects of junk food and soft drinks on the health of school children, Sonali, a student of Class XII, discussed the issue with the school principal. Principal immediately instructed the canteen contractor to replace the fast food with the fibre and vitamins rich food like sprouts, salad, fruits etc. This decision was welcomed by the parents and the students.

(a) What value are expressed by Sonali and the Principal of the school?

(b) Give two examples of water-soluble vitamins.

Chapter: [14.03] Vitamins
Concept: Introduction of Vitamins
[3]27

Which one of the following is a food preservative?

Equanil, Morphine, Sodium benzoate

Chapter: [16.02] Chemicals in Food
Concept: Chemicals in Food - Artificial Sweetening Agents and Food Preservatives

Why is bithional added to soap?

Chapter: [16.03] Cleansing Agents
Concept: Cleansing Agents - Soaps

Which class of drugs is used in sleeping pills?

Chapter: [16.01] Chemicals in Medicines
Concept: Drugs and Their Classification
[5]28 | Attempt any one of the following
[5]28.1

A reaction is second order in A and first order in B.

(i) Write the differential rate equation.

(ii) How is the rate affected on increasing the concentration of A three times?

(iii) How is the rate affected when the concentrations of both A and B are doubled?

Chapter: [5] Chemical Kinetics
Concept: Factors Influencing Rate of a Reaction

A first order reaction takes 40 minutes for 30% decomposition. Calculate t1/2 for this reaction. (Given log 1.428 = 0.1548)

Chapter: [5] Chemical Kinetics
Concept: Integrated Rate Equations - Half-life of a Reaction
[5]28.2

For a first order reaction, show that time required for 99% completion is twice the time required for the completion of 90% of reaction.

Chapter: [5] Chemical Kinetics
Concept: Integrated Rate Equations - Half-life of a Reaction

(b) Rate constant ‘k’ of a reaction varies with temperature ‘T’ according to the equation:

logk=logA-E_a/2.303R(1/T)

Where Ea is the activation energy. When a graph is plotted for logk Vs. 1/T a straight line with a slope of −4250 K is obtained. Calculate ‘Ea’ for the reaction.(R = 8.314 JK−1 mol−1)

Chapter: [5] Chemical Kinetics
Concept: Temperature Dependence of the Rate of a Reaction
[5]29 | Attempt any one of the following
[5]29.1
[3]29.1.1

Give reasons for the following:

(i) Bond enthalpy of F2 is lower than that of Cl2.

(ii) PH3 has lower boiling point than NH3.

Chapter: [9] Coordination Compounds
Concept: Bonding in Coordination Compounds - Introduction
[3]29.1.2

Draw the structures of the following molecules: XeF4

Chapter: [8] Chemistry of p-Block Elements: Group 16, 17, 18
Concept: P - Block Group 18 Elements - Concept of Group 18 Elements

Draw the structures of the following molecules: BrF3

Chapter: [8] Chemistry of p-Block Elements: Group 16, 17, 18
Concept: P - Block Group 17 Elements - Interhalogen Compounds

Draw the structures of the following molecules: (HPO3)3

Chapter: [7.01] Group 15 Elements
Concept: P - Block Group 15 Elements - Compounds of Phosphorus
[5]29.2
[3]29.2.1

Account for the following:

Helium is used in diving apparatus.

Chapter: [8] Chemistry of p-Block Elements: Group 16, 17, 18
Concept: P - Block Group 18 Elements - Concept of Group 18 Elements

Account for the following: Fluorine does not exhibit positive oxidation state.

Chapter: [7.03] Group 17 Elements
Concept: P - Block Group 17 Elements - Concept of Group 17 Elements

Account for the following: Oxygen shows catenation behavior less than sulphur.

Chapter: [8] Chemistry of p-Block Elements: Group 16, 17, 18
Concept: Concept of Group 16 Elements
[3]29.2.2

Draw the structures of the following molecules: XeF2

Chapter: [8] Chemistry of p-Block Elements: Group 16, 17, 18
Concept: P - Block Group 18 Elements - Concept of Group 18 Elements

Draw the structures of the following molecules: H2S2O8

Chapter: [7.02] Group 16 Elements
Concept: P - Block Group 16 Elements - Oxoacids of Sulphur
[5]30 | Attempt any one of the following
[5]30.1
[3]30.1.1

Although phenoxide ion has more number of resonating structures than Carboxylate ion, Carboxylic acid is a stronger acid than phenol. Give two reasons.

Chapter: [12] Aldehydes, Ketones and Carboxylic Acids
Concept: Carboxylic Acids - Chemical Reactions of Carboxylic Acids - Reactions Involving Cleavege of O-H Bond
[2]30.1.2

How will you bring about the following conversions?

Propanone to propane

Chapter: [12] Aldehydes, Ketones and Carboxylic Acids
Concept: Aldehydes and Ketones - Chemical Reactions of Aldehydes and Ketones - Reduction

How will you bring about the following conversion?

Benzoyl chloride to benzaldehyde

Chapter: [14.02] Acid derivatives
Concept: Aldehydes and Ketones - Preparation of Aldehydes

How will you bring about the following conversion?

Ethanal to but-2-enal

Chapter: [12] Aldehydes, Ketones and Carboxylic Acids
Concept: Aldehydes and Ketones - Chemical Reactions of Aldehydes and Ketones - Reactions Due to A-hydrogen
[5]30.2
[3]30.2.1

Complete the following reactions:

Chapter: [12.01] Aldehydes and Ketones
Concept: Aldehydes and Ketones - Chemical Reactions of Aldehydes and Ketones - Other Reactions

Complete the following reactions:

Chapter: [12.01] Aldehydes and Ketones
Concept: Aldehydes and Ketones - Chemical Reactions of Aldehydes and Ketones - Other Reactions

Complete the following reactions:

Chapter: [12.01] Aldehydes and Ketones
Concept: Aldehydes and Ketones - Chemical Reactions of Aldehydes and Ketones - Other Reactions
[2]30.2.2

Give simple chemical tests to distinguish between the following pairs of compounds:

Ethanal and Propanal

Chapter: [12] Aldehydes, Ketones and Carboxylic Acids
Concept: Aldehydes and Ketones - Chemical Reactions of Aldehydes and Ketones - Oxidation

Give simple chemical tests to distinguish between the following pairs of compounds:  Benzoic acid and Phenol

Chapter: [12.05] Distinction between primary, secondary and tertiary alcohols
Concept: Chemical Reactions of Phenols (Only)
S