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# Chemistry 56/1/3 2018-2019 CBSE (Science) Class 12 Question Paper Solution

Chemistry [56/1/3]
Date & Time: 13th March 2019, 10:30 am
Duration: 3h
• All questions are compulsory
• Section A: Q. no. 1 to 5 are very short-answer questions and carry 1 mark each.
• Section B: Q. no. 6 to 12 are short-answer questions and carry 2 marks each.
• Section C: Q. no. 13 to 24 are also short-answer questions and carry 3 marks each.
• Section D: Q. no. 25 to 27 are long-answer questions and carry 5 marks each.

SECTION - A
[1]1

Arrange the following in decreasing order of solubility in water:
$\ce{(CH3)3N,(CH3)2NH,CH3NH2}$

Concept: Solubility - Introduction
Chapter: [2] Solutions
[1]2

What type of stoichiometric defect is shown by ZnS and why?

Concept: Imperfections in Solids - Types of Point Defects - Stoichiometric Defects
Chapter: [1] Solid State
[1]3

Write one stereochemical difference between SN1 and SN2 reactions.

Concept: Chemical Reactions of Haloalkanes and Haloarenes - Reactions of Haloalkanes - Nucleophilic Substitution Reactions
Chapter: [10] Haloalkanes and Haloarenes
[1]4
[1]4.1

Why are medicines more effective in the colloidal state?

Concept: Properties of Colloidal Solutions
Chapter: [5] Surface Chemistry
OR
[1]4.2

What is the difference between an emulsion and a gel?

Concept: Emulsions
Chapter: [5] Surface Chemistry
[1]5
[1]5.1

What is the basic structural difference between glucose and fructose?

Concept: Carbohydrates - Structures of Glucose
Chapter: [14] Biomolecules
OR
[1]5.2

Write the products obtained after the hydrolysis of lactose.

Concept: Carbohydrates - Disaccharides - Sucrose, Maltose and Lactose
Chapter: [14] Biomolecules
SECTION - B
[2]6

When MnO2 is fused with KOH in the presence of KNO3 as an oxidizing agent, it gives a dark green compound (A). Compound (A) disproportionates in an acidic solution to give a purple compound (B).  An alkaline solution of compound (B) oxidizes KI to compound (C) whereas an acidified solution of compound (B) oxidizes KI to (D). Identify (A), (B), (C), and (D).

Concept: Some Important Compounds of Transition Elements - Oxides and Oxoanions of Metals
Chapter: [8] "D" and "F" Block Elements
[2]7

State Henry's law and write its two applications.

Concept: Solubility - Solubility of a Gas in a Liquid
Chapter: [2] Solutions
[2]8
[2]8.1

Write IUPAC name of the complex [Pt(en)2CI2]. Draw structures of geometrical isomers for this complex.

Concept: Isomerism in Coordination Compounds - Stereoisomerism
Chapter: [9] Coordination Compounds
OR
[2]8.2

Using IUPAC norms write the formulae for the following:
Hexaamminecobalt(III) sulphate

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

Using IUPAC norms write the formulae for the following:
Potassium trioxalatochromate (III)

Concept: Haloalkanes and Haloarenes - Nomenclature
Chapter: [10] Haloalkanes and Haloarenes
[2]9
[2]9.1

Write a balanced chemical equation for the following process:
XeF2 undergoes hydrolysis.

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

Write a balanced chemical equation for the following process:
MnO2 is heated with conc.HCI

Concept: Rate of a Chemical Reaction
Chapter: [4] Chemical Kinetics
OR
[2]9.2

Arrange the following in the order of the property indicated against set :
H2O, H2S, H2Se, H2Te − increasing acidic character.

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

Arrange the following in order of the property indicated set.
HF, HCl, HBr, HI - decreasing bond enthalpy.

Concept: Concept of Group 16 Elements
Chapter: [7] P - Block Elements
[2]10

For a reaction
$\ce{2H2O2->[I^-][Alkaline medium]2H2O + O2}$

The Proposed mechanism is given below:
(1) H2O2+I- → H2O+IO-(slow)
(2) H2O2+IO-→H2O+I-+O2(fast)

(i) Write the rate law for the reaction.
(ii) Write the overall order of a reaction.
(iii) Out of steps(1) and (2), which one is the rate-determining step?

Concept: Catalyst - Effect of Catalyst on the Rate of Reaction
Chapter: [4] Chemical Kinetics
[2]11

Write the hybridization and magnetic character of the following complexes:
[Fe(H2O)6]2+
(Atomic no. of Fe = 26)

Concept: Bonding in Coordination Compounds - Magnetic Properties of Coordination Compounds
Chapter: [9] Coordination Compounds

Write the hybridization and magnetic character of the following complexes:
[Fe(CO)5]
(Atomic no. of Fe = 26)

Concept: Bonding in Coordination Compounds - Magnetic Properties of Coordination Compounds
Chapter: [9] Coordination Compounds
[2]12

Write the structure of main compounds A and B in the following reaction:

$\ce{CH3CH2CN->[CH3MgBRH/3O+]A->[LiAIH4]B}$

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

Write the structure of main compounds A and B in the following reaction:

Concept: Chemical Reactions of Haloalkanes and Haloarenes - Reactions of Haloalkanes - Reaction with Metals
Chapter: [10] Haloalkanes and Haloarenes
SECTION - C
[3]13
[1]13.1

Complete the following reaction:

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

Complete the following reaction:
$\ce{(C6H5CH2)2Cd + 2CH3COCI}$

Concept: Aldehydes and Ketones - Preparation of Aldehydes and Ketones
Chapter: [12] Aldehydes, Ketones and Carboxylic Acids

Complete the following reaction:

$\begin{array}{cc} \ce{CH3}\phantom{..............}\\ |\phantom{..............}\phantom{...}\\ \ce{CH3-CH-COOH->[(i) Br2/Red P4][(ii) H2O]}\\ \phantom{.......}\ \end{array}$

Concept: Introduction of Carboxylic Acids
Chapter: [12] Aldehydes, Ketones and Carboxylic Acids
OR
[3]13.2

Write a chemical equation for the following reaction:
Propanone is treated with dilute Ba( OH)2.

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

Write chemical equation of the following reaction :
Acetophenone is treated with ("Zn"("Hg"))/"Conc.HCl".

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

Write chemical equations of the following reaction :
Benzoyl chloride is hydrogenated in the presence of "Pd"/(BaSO_4)

Concept: Aldehydes and Ketones - Chemical Reactions of Aldehydes and Ketones - Reactions Due to A-hydrogen
Chapter: [12] Aldehydes, Ketones and Carboxylic Acids
[3]14

What is the role of activated charcoal in gas masks?

Concept: Types of Solutions
Chapter: [2] Solutions

A colloidal sol is prepared by the given method in the figure. What is the charge on hydrated ferric oxide colloidal particles formed in the test tube? How is the sol represented?

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

How does chemisorption vary with temperature?

Chapter: [5] Surface Chemistry
[3]15

A 4% solution(w/w) of sucrose (M = 342 g mol−1) in water has a freezing point of 271.15 K. Calculate the freezing point of 5% glucose (M = 180 g mol−1) in water.
(Given: Freezing point of pure water = 273.15 K)

Concept: Colligative Properties and Determination of Molar Mass - Depression of Freezing Point
Chapter: [2] Solutions
[3]16

An element crystallizes in fcc lattice with a cell edge of 300 pm. The density of the element is 10.8 g cm−3. Calculate the number of atoms in 108 g of the element.

Concept: Calculations Involving Unit Cell Dimensions
Chapter: [1] Solid State
[3]17

How will you convert the following:
Impure Nickel to pure Nickel

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

How will you convert the following:
Zinc blende to Zinc metal

Concept: Application of Thermodynamic Principles of Metallurgy
Chapter: [6] General Principles and Processes of Isolation of Elements

How will you convert the following:
[Ag(CN)2] to Ag

Concept: Occurrence of Metals
Chapter: [6] General Principles and Processes of Isolation of Elements
[3]18

Give reasons for the following:
The transition metals generally form coloured compounds.

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

Give reasons for the following:
E⁰ value for (Mn3+|Mn2+) is highly positive than that for (Cr3+|Cr2+) couple.

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

Give reasons for the following:
The chemistry of actinoids elements is not so smooth as that of the lanthanoids.

Concept: F-block Elements - The Actinoids
Chapter: [8] "D" and "F" Block Elements
[3]19
[1]19.1

Why type of drug is used in sleeping pills?

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

What type of detergent are used in toothpastes?

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

Why the use of alitame as an artificial sweetener is not recommended?

Concept: Chemicals in Food - Artificial Sweetening Agents and Food Preservatives
Chapter: [16] Chemistry in Everyday Life
OR
[1]19.2

Define the following term with a suitable example in each:

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

Define the following term with a suitable example in each:
Disinfectants

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

Define the following term with a suitable example in each:
Cationic detergents

Concept: Cleansing Agents - Synthetic Detergents
Chapter: [16] Chemistry in Everyday Life
[3]20
[1]20.1

Write the structures of monomers used the following polymers:
Nylon - 6, 6

Concept: Types of Polymerisation Reactions - Condensation Polymerisation Or Step Growth Polymerisation
Chapter: [15] Polymers

Write the structures of monomers used the following polymers:
Glyptal

Concept: Polymers of Commercial Importance
Chapter: [15] Polymers

Write the structures of monomers used the following polymers:
Buna S

Concept: Types of Polymerisation Reactions - Rubber
Chapter: [15] Polymers
OR
[1]20.2

Is   a homopolymer or copolymer? Give reason.

Concept: Types of Polymerisation Reactions - Copolymerisation
Chapter: [15] Polymers

Write the monomers of the following polymer :

Concept: Polymers - Some Important Polymers
Chapter: [15] Polymers

What is the role of Sulphur in the vulcanization of rubber?

Concept: Types of Polymerisation Reactions - Rubber
Chapter: [15] Polymers
[3]21

Out of (CH3)3 C-Br and (CH3)3 C-I, which one is more reactive towards SN1 and why?

Concept: Chemical Reactions of Haloalkanes and Haloarenes - Reactions of Haloarenes - Nucleophilic Substitution
Chapter: [10] Haloalkanes and Haloarenes

Write the product formed when p-nitro chlorobenzene is heated with aqueous  NaOH at 443K followed by acidification?

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

Why dextro and laevo rotatory isomers of Butan-2-ol are difficult to separate by fractional distillation?

Concept: Isomerism in Coordination Compounds - Introduction
Chapter: [9] Coordination Compounds
[3]22

Write equations of the following reactions:
Acetylation of aniline

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

Write equations of the following reactions:
Coupling reaction

Concept: Diazonium Salts - Chemical Reaction of Diazonium Salts - Reactions Involving Retention of Diazo Group Coupling Reactions
Chapter: [13] Organic Compounds Containing Nitrogen

Write equations of the following reactions:
Carbyl amine reaction

Concept: Amines - Chemical Reactions of Amines - Carbylamine Reaction
Chapter: [13] Organic Compounds Containing Nitrogen
[3]23

The decomposition of NH3 on a platinum surface is a zero-order reaction. If the rate constant (k)  is 4 x 10-3 ms-1, how long will it take to reduce the initial concentration of NH3 from 0.1 M to 0.064 M?

Concept: Integrated Rate Equations - Zero Order Reactions
Chapter: [4] Chemical Kinetics
[3]24
[3]24.1

Define the following term:
Oligosaccharides

Concept: Carbohydrates - Oligosaccharides
Chapter: [14] Biomolecules

Define the following term:
Denaturation of protein

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

Define the following term:
Vitamins

Concept: Vitamins - Classification of Vitamins
Chapter: [14] Biomolecules
OR
[3]24.2

Write the reactions involved when D-glucose is treated with the following reagent:
Br2 water

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

Write the reactions involved when D-glucose is treated with the following reagent:
H2N-OH

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

Write the reactions involved when D-glucose is treated with the following reagent:
(CH3CO)2O

Concept: Carbohydrates - Structures of Glucose
Chapter: [14] Biomolecules
SECTION - D
[5]25
[1]25.1

How do you convert the following :
Phenol to anisole

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

How do you convert the following :
Ethanol to Propan-2-ol

Concept: Some Commercially Important Alcohols
Chapter: [11] Alcohols, Phenols and Ethers
[1]25.2

Write the mechanism of the following reaction :

$\ce{C2H5OH->[H2SO4][443K]CH2=CH2 + H2O}$

Concept: Some Commercially Important Alcohols
Chapter: [11] Alcohols, Phenols and Ethers
[3]25.3

Why phenol undergoes electrophilic substitution more easily than benzene?

Concept: Preparation of Phenols from Haloarenes, Benzenesulphonic Acid, Diazonium Salts and Cumene
Chapter: [11] Alcohols, Phenols and Ethers
OR
[1]25.4

Account for the following:
o-nitrophenol is more steam volatile than p-nitrophenol.

Concept: Chemical Reactions of Alcohols and Phenols - Reactions Involving Cleavage of O–H Bond
Chapter: [11] Alcohols, Phenols and Ethers

Account for the following :
t-butyl chloride on heating with sodium methoxide gives 2-methylpropene instead of t-butyl methyl ether.

Concept: Preparation of Ethers from Dehydration of Alcohols and Williamson Systhesis
Chapter: [11] Alcohols, Phenols and Ethers
[1]25.5

Write the reaction involved in the following:
Reimer-Tiemann reaction

Concept: Chemical Reactions of Phenols (Only)
Chapter: [11] Alcohols, Phenols and Ethers

Write the reaction involved in the following:
Friedal-Crafts Alkylation of Phenol

Concept: Chemical Reactions of Phenols (Only)
Chapter: [11] Alcohols, Phenols and Ethers
[3]25.6

Give simple chemical test to distinguish between Ethanol and Phenol.

Concept: Some Commercially Important Alcohols
Chapter: [11] Alcohols, Phenols and Ethers
[5]26
[3]26.1

Give reasons for the following:
Sulphur in vapour state shows paramagnetic behaviour.

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

Give reasons for the following:
N-N bond is weaker than P-P bond.

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

Give reasons for the following:
Ozone is thermodynamically less stable than oxygen.

Concept: P - Block Group 16 Elements - Ozone
Chapter: [7] P - Block Elements
[2]26.2

Write the name of gas released when Cu is added to
dilute HNO3

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

Write the name of gas released when Cu is added to
conc. HNO3

Concept: P - Block Group 15 Elements - Nitric Acid
Chapter: [7] P - Block Elements
OR
[2]26.3

Write the disproportionation reaction of H3PO3

Concept: P - Block Group 15 Elements - Phosphorus - Allotropic Forms
Chapter: [7] P - Block Elements

Draw the structure of XeF4

Concept: P - Block Group 18 Elements - Concept of Group 18 Elements
Chapter: [7] P - Block Elements
[2]26.4

Account for the following :
Although Fluorine has less negative electron gain enthalpy yet F2 is a strong oxidizing agent.

Concept: P Block Elements
Chapter: [7] P - Block Elements

Account for the following :
Acidic character decreases from N2O3 to Bi2O3 in group 15.

Concept: Concept of Group 15 Elements
Chapter: [7] P - Block Elements
[1]26.5

Write a chemical reaction to test sulphur dioxide gas. write a chemical equation involved.

Concept: P - Block Group 16 Elements - Sulphur Dioxide
Chapter: [7] P - Block Elements
[5]27
[5]27.1

cell for the given redox reaction is 2.71 V
Mg(s) + Cu2+ (0.01 M) → Mg2+ (0.001 M) + Cu(s)

Calculate Ecell for the reaction. Write the direction of flow of current when an external opposite potential applied is
(i) less than 2.71 V and
(ii) greater than 2.71 V

Concept: Electrochemical Cells
Chapter: [3] Electrochemistry
OR
[5]27.2
[3]27.2.1

Solve the following question.
A steady current of 2 amperes was passed through two electrolytic cells X and Y connected in series containing electrolytes FeSO4 and ZnSO4 until 2.8 g of Fe deposited at the cathode of cell X. How long did the current flow? Calculate the mass of Zn deposited at the cathode of cell Y.
(Molar mass : Fe = 56 g mol–1, Zn = 65.3 g mol–1, 1F = 96500 C mol–1)

Concept: Electrolytic Cells and Electrolysis - Introduction
Chapter: [3] Electrochemistry
[2]27.2.2

In the plot of molar conductivity (∧m) vs square root of concentration (c1/2), following curves are obtained for two electrolytes A and B:

(i) Predict the nature of electrolytes A and B.
(ii) What happens on extrapolation of ∧m to concentration approaching zero for electrolytes A and B?

Concept: Conductance of Electrolytic Solutions - Variation of Conductivity and Molar Conductivity with Concentration
Chapter: [3] Electrochemistry

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## CBSE previous year question papers Class 12 Chemistry with solutions 2018 - 2019

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