CBSE (Commerce) Class 12CBSE
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Question Paper Solutions - Chemistry 2017 - 2018 CBSE (Commerce) Class 12

Alternate Sets

   

Marks: 70
[1]1

An analysis shows that FeO has a non-stoichiometric composition with formula Fe0.95O. Give reason.

Chapter: [8] "D" and "F" Block Elements
Concept: General Properties of the Transition Elements (D-block)
[1]2

CO (g) and H2 (g) react to give different products in the presence of different catalysts. Which ability of the catalyst is shown by these reactions?

Chapter: [5] Surface Chemistry
Concept: Catalysis - Catalysts in Industry
[1]3

Write the coordination number and oxidation state of Platinum in the complex [Pt(en)2Cl2].

Chapter: [9] Coordination Compounds
Concept: Coordination Compounds Numerical
[1]4

Out of chlorobenzene and benzyl chloride, which one gets easily hydrolysed by aqueous NaOH and why?

Chapter: [7] P - Block Elements
Concept: Compounds of Halogens
[1]5

Write the IUPAC name of the following :

Chapter: [11] Alcohols, Phenols and Ethers
Concept: Alcohols, Phenols and Ethers - Nomenclature
[2]6

Calculate the freezing point of a solution containing 60 g of glucose (Molar mass = 180 g mol–1) in 250 g of water. (Kf of water = 1.86 K kg mol–1)

Chapter: [2] Solutions
Concept: Colligative Properties and Determination of Molar Mass - Depression of Freezing Point
[2]7

For the reaction 

2N2O5 (g) → 4NO2 (g) + O2 (g), the rate of formation of NO2 (g) is 2·8 × 10–3 M s–1. Calculate the rate of disappearance of N2O5 (g).

Chapter: [4] Chemical Kinetics
Concept: Rate of a Chemical Reaction
[2]8

Among the hydrides of Group-15 elements, which have the lowest boiling point?

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

Among the hydrides of Group-15 elements, which have the maximum basic character?

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

Among the hydrides of Group-15 elements, which have the highest bond angle?

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

Among the hydrides of Group-15 elements, which have the maximum reducing character?

Chapter: [7] P - Block Elements
Concept: Concept of Group 15 Elements
[2]9 | Attempt Any One
[2]9.1

How do you convert the Ethanal to Propanone

Chapter: [11] Alcohols, Phenols and Ethers
Concept: Alcohols, Phenols and Ethers - Nomenclature

How do you convert the Toluene to Benzoic acid

Chapter: [12] Aldehydes, Ketones and Carboxylic Acids
Concept: Carboxylic Acids - Nomenclature
[2]9.2

Account for the following:

Aromatic carboxylic acids do not undergo Friedel-Crafts reaction.

Chapter: [12] Aldehydes, Ketones and Carboxylic Acids
Concept: Carboxylic Acids - Structure of the Carboxyl group

Account for the following:

pKa value of 4-nitrobenzoic acid is lower than that of benzoic acid.

Chapter: [12] Aldehydes, Ketones and Carboxylic Acids
Concept: Physical Properties of Carboxylic Acids
[2]10

Complete and balance the following chemical equations

`Fe^(2+) + MnO_4^(-) + H^+ ->`

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

Complete and balance the following chemical equations

`MnO_4^(-) + H_2O + I^(-) ->`

Chapter: [8] "D" and "F" Block Elements
Concept: General Properties of the Transition Elements (D-block)
[3]11

Give reasons for the following:

Measurement of osmotic pressure method is preferred for the determination of molar masses of macromolecules such as proteins and polymers.

Chapter: [2] Solutions
Concept: Colligative Properties and Determination of Molar Mass - Depression of Freezing Point

Give reasons for the following :

Aquatic animals are more comfortable in the cold water than in warm water.

Chapter: [2] Solutions
Concept: Solubility - Solubility of a Gas in a Liquid

Give reasons for the following

Elevation of the boiling point of 1 M KCl solution is nearly double than that of 1 M sugar solution.

Chapter: [2] Solutions
Concept: Abnormal Molar Masses
[3]12

An element 'X' (At. mass = 40 g mol-1) having f.c.c. the structure has unit cell edge length of 400 pm. Calculate the density of 'X' and the number of unit cells in 4 g of 'X'. (NA = 6.022 × 1023 mol-1)

Chapter: [1] Solid State
Concept: Number of Atoms in a Unit Cell
[3]13

A first-order reaction is 50% completed in 40 minutes at 300 K and in 20 minutes at 320 K. Calculate the activation energy of the reaction. (Given : log 2 = 0·3010, log 4 = 0·6021, R = 8·314 JK–1 mol–1)

Chapter: [4] Chemical Kinetics
Concept: Temperature Dependence of the Rate of a Reaction
[3]14

What happens when a freshly prepared precipitate of Fe(OH)3 is shaken with a small amount of FeCl3 solution?

Chapter: [5] Surface Chemistry
Concept: Properties of Colloidal Solutions

What happens when persistent dialysis of a colloidal solution is carried out?

Chapter: [5] Surface Chemistry
Concept: Properties of Colloidal Solutions

What happens when an emulsion is centrifuged?

Chapter: [5] Surface Chemistry
Concept: Properties of Colloidal Solutions
[3]15

Write the chemical reactions involved in the process of extraction of Gold. Explain the role of dilute NaCN and Zn in this process.

Chapter: [6] General Principles and Processes of Isolation of Elements
Concept: Concentration of Ores - Leaching
[3]16

Give reasons: E° value for the Mn3+/Mn2+ couple is much more positive than that for Fe3+/Fe2+.

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

Give reasons Iron has the higher enthalpy of atomization than that of copper.

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

Give reasons: Sc3+ is colourless in aqueous solution whereas Ti3+ is coloured.

Chapter: [8] "D" and "F" Block Elements
Concept: General Properties of the Transition Elements (D-block)
[3]17

Identify the chiral molecule in the following pair :

 

Chapter: [11] Alcohols, Phenols and Ethers
Concept: Physical and Chemical Properties of Alcohols and Phenols

Write the structure of the product when chlorobenzene is treated with methyl chloride in the presence of sodium metal and dry ether.

Chapter: [7] P - Block Elements
Concept: Compounds of Halogens

Write the structure of the alkene formed by dehydrohalogenation of 1-Bromo-1methylcyclohexane with alcoholic KOH.

Chapter: [7] P - Block Elements
Concept: Compounds of Halogens
[3]18

(A), (B) and (C) are three non-cyclic functional isomers of a carbonyl compound with molecular formula C4H8O. Isomers (A) and (C) give positive Tollens' test whereas isomer (B) does not give Tollens' test but gives positive Iodoform test. Isomers (A) and (B) on reduction with Zn(Hg)/conc. HCl give the same product (D).

1) Write the structures of (A), (B), (C) and (D).

2) Out of (A), (B), and (C) isomers, which one is least reactive towards the addition of HCN?

Chapter: [9] Coordination Compounds
Concept: Bonding in Metal Carbonyls
[3]19

Write the structures of the main products in the following reactions :

Chapter: [9] Coordination Compounds
Concept: Importance and Applications of Coordination Compounds

Write the structures of the main products in the following reactions :

Chapter: [10] Haloalkanes and Haloarenes
Concept: Haloalkanes and Haloarenes - Nomenclature

Write the structures of the main products in the following reactions :

Chapter: [11] Alcohols, Phenols and Ethers
Concept: Chemical Reaction of Ethers - Cleavege of C-O Bonds
[3]20

Why is bithional added to soap?

Chapter: [16] Chemistry in Everyday Life
Concept: Cleansing Agents - Soaps

What is tincture of iodine? What is its use?

Chapter: [16] Chemistry in Everyday Life
Concept: Therapeutic Action of Different Classes of Drugs - Antimicrobials

Among the following, which one acts as a food preservative?

Aspartame, Aspirin, Sodium Benzoate, Paracetamol

Chapter: [16] Chemistry in Everyday Life
Concept: Chemicals in Food - Artificial Sweetening Agents and Food Preservatives
[3]21 | Attempt Any One
[3]21.1

Define the following with an example of each

Polysaccharides

Chapter: [14] Biomolecules
Concept: Carbohydrates - Polysaccharides - Starch, Cellulose and Glycogen

Define the following with an example

Denatured protein

Chapter: [14] Biomolecules
Concept: Proteins - Denaturation of Proteins

Define the following terms: Essential amino acids

Chapter: [14] Biomolecules
Concept: Proteins - Amino Acids
[3]21.2

Write the product when D-glucose reacts with conc. HNO3.

Chapter: [14] Biomolecules
Concept: Carbohydrates - Structures of Glucose

Amino acids show amphoteric behaviour. Why?

Chapter: [14] Biomolecules
Concept: Proteins - Amino Acids

Write one difference between α-helix and β-pleated structures of proteins.

Chapter: [14] Biomolecules
Concept: Proteins - Structure of Proteins
[3]22

Write the formulas for the following coordination compounds:

Iron(III) hexacyanoferrate(II)

Chapter: [9] Coordination Compounds
Concept: Introduction of Coordination Compounds

What type of isomerism is exhibited by the complex `[Co(NH_3)_5Cl]SO_4`?

Chapter: [9] Coordination Compounds
Concept: Isomerism in Coordination Compounds - Structural Isomerism

Write the hybridisation and number of unpaired electrons in the complex `[CoF_6]^(3-)`. (Atomic No. of Co = 27)

Chapter: [9] Coordination Compounds
Concept: Bonding in Coordination Compounds - Valence Bond Theory (VBT)
[4]23

Shyam went to a grocery shop to purchase some food items. The shopkeeper packed all the items in polythene bags and gave them to Shyam. But Shyam refused to accept the polythene bags and asked the shopkeeper to pack the items in paper bags. He informed the shopkeeper about the heavy penalty imposed by the government for using polythene bags. The shopkeeper promised that he would use paper bags in future in place of polythene bags.

1) Write the values (at least two) shown by Shyam.

2) Write one structural difference between low-density polyethene and high-density polyethene.

3) Why did Shyam refuse to accept the items in polythene bags?

4) What is a biodegradable polymer? Give an example.

 

Chapter: [15] Polymers
Concept: Polymers - Classification of Polymers Based on Mode of Polymerisation
[5]24 | Attempt Any One
[5]24.1

Give reasons H3PO3 undergoes disproportionation reaction but H3PO4 does not.

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

Give reasons When Cl2 reacts with the excess of F2, ClF3 is formed and not FCl3.

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

Give reasons Dioxygen is a gas while Sulphur is a solid at room temperature.

Chapter: [7] P - Block Elements
Concept: P - Block Group 16 Elements - Sulphur - Allotropic Forms

Draw the structures of the following molecules: XeF4

Chapter: [7] P - Block Elements
Concept: P - Block Group 18 Elements - Concept of Group 18 Elements

Draw the structures of the HClO3

Chapter: [7] P - Block Elements
Concept: P - Block Group 17 Elements - Oxoacids of Halogens
[5]24.2

When concentrated sulphuric acid was added to an unknown salt present in a test tube a brown gas (A) was evolved. This gas intensified when copper turnings were added to this test tube. On cooling, the gas (A) changed into a colourless solid (B).

1) Identify (A) and (B).

2) Write the structures of (A) and (B).

3) Why does gas (A) change to solid on cooling?

Chapter: [7] P - Block Elements
Concept: P - Block Group 16 Elements - Sulphuric Acid

Arrange the following in the decreasing order of their reducing character :

HF, HCl, HBr, HI

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

What happens when: XeF4 reacts with SbF5?

Chapter: [7] P - Block Elements
Concept: P - Block Group 18 Elements - Concept of Group 18 Elements
[5]25 | Attempt Any One
[5]25.1

Write the cell reaction and calculate the e.m.f of the following cell at 298 K:

`Sn(s) | Sn^(2+) (0.004 M) || H^(+) (0.020 M) | H_2 (g) ("1 bar") | Pt(s)`

(Given: `E_(Sn^(2+)"/"Sn)^0 = -0.14` V)

Chapter: [3] Electrochemistry
Concept: Galvanic Cells - Measurement of Electrode Potential

Give reasons On the basis of E° values, O2 gas should be liberated at anode but it is Cl2 gas which is liberated in the electrolysis of aqueous NaCl.

Chapter: [3] Electrochemistry
Concept: Conductance of Electrolytic Solutions - Measurement of the Conductivity of Ionic Solutions

Give reasons Conductivity of CH3COOH decreases on dilution.

Chapter: [3] Electrochemistry
Concept: Conductance of Electrolytic Solutions - Measurement of the Conductivity of Ionic Solutions
[5]25.2

For the reaction

`2AgCl (s) + H_2 (g) ("1 atm") -> 2Ag (s) + 2H^(+)  (0.1 M) +  2Cl^(-) (0.1 M)`

`triangleG^0 = -43600 J at 25^@ C`

Calculate the e.m.f. of the cell

`[log 10^(-n) = -n]` 

Chapter: [3] Electrochemistry
Concept: Relation Between Gibbs Energy Change and Emf of a Cell

Define terms: Fuel cell

Chapter: [3] Electrochemistry
Concept: Batteries - Primary Batteries

Write two advantages of fuel cell

Chapter: [3] Electrochemistry
Concept: Fuel Cells
[5]26
[5]26.1

Write the chemical equations involved in the following reactions:(i) Hoffmann-bromamide degradation reaction

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Amines - Preparation of Amines

Illustrate the following reaction giving suitable example in each case: Diazotisation

 

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Diazonium Salts - Method of Preparation of Diazonium Salts

Illustrate the following reaction giving suitable example in each case:Gabriel phthalimide synthesis

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Amines - Preparation of Amines

Give reason (CH3)2NH is more basic than (CH3)3N in an aqueous solution.

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Physical Properties of Amines

Give reason Aromatic diazonium salts are more stable than aliphatic diazonium salts.

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Physical Properties of Diazonium Salts
[5]26.2

Write the structures of the main products of the following reactions:

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Amines - Chemical Reactions of Amines - Basic Character of Amines

Write the structures of the main products of the following reactions:

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Amines - Chemical Reactions of Amines - Basic Character of Amines

Write the structures of the main products of the following reactions:

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Amines - Chemical Reactions of Amines - Basic Character of Amines

Give a simple chemical test to distinguish between Aniline and N, N-dimethylaniline

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Amines - Chemical Reactions of Amines - Carbylamine Reaction

Arrange the following in the increasing order of their pKvalues:

C6H5NH2, C2H5NH2, C6H5NHCH3

Chapter: [13] Organic Compounds Containing Nitrogen
Concept: Amines - Preparation of Amines
S