Chemistry (Theory) Official 2022-2023 ISC (Science) ISC Class 12 Question Paper Solution

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Chemistry (Theory) [Official]
Marks: 70 CISCE
ISC (Science)

Academic Year: 2022-2023
Date & Time: 27th February 2023, 2:00 pm
Duration: 3h
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  1. Candidates are allowed an additional 15 minutes for only reading the paper.
  2. They must NOT start writing during this time.
  3. This paper is divided into four sections A, B, C and D.
  4. Answer all questions.
  5. Section A consists of one question having sub-parts of one mark each.
  6. Section B consists of ten questions of tuwo marks each.
  7. Section C consists of seven questions of three marks each and
  8. Section D consists of three quesfions of five marks each.
  9. Internal choices have been provided in one question each in Section B, Section C and Section D.
  10. All working, including rough work, should be done on the same sheet as, and adjacent to the rest of the answer.
  11. The intended marks for questions or parts of questions are given in brackets [].
  12. Balanced equations must be given wherever possible and diagrams where they are helpful.
  13. When solving numerical problems, all essential working must be shown.
  14. In working out problems, use the following data :
    Gas constant R = 1.987 cal deg-1 mol-1 = 8.314 JK-1mol-1 = 0.0821 dm3 atm K-1 mol-1
    1 l. 1 atm =1 dm3 atm = 101.3 J.
    1 Faraday = 96500 coulombs.
    Avogadro's number = 6.023 x 1023

SECTION A - 14 MARKS
[14]1
[4]1.i
[1]1.i.a

Fill in the blanks by choosing the appropriate words from those given in the brackets:

[stable, low, aldehyde, unstable, 6, 4, ethane, Clemmensen’s, 2, 3, carboxylic acid, high, propane, Rosenmund's]

The primary alcohols are easily oxidised first into ______ and then into ______.

Concept: Acids - Methods of Preparation of Carboxylic Acids
Chapter: [0.141] Carboxylic acids
[1]1.i.b

Fill in the blanks by choosing the appropriate words from those given in the brackets:

[stable, low, aldehyde, unstable, 6, 4, ethane, Clemmensen’s, 2, 3, carboxylic acid, high, propane, Rosenmund's]

The intermediate activated complex in a chemical reaction is highly ______ due to ______ energy.

Concept: Collision Theory - Activated Complex Formation
Chapter: [0.0302] Collision Theory
[1]1.i.c

Fill in the blanks by choosing the appropriate words from those given in the brackets:

[stable, low, aldehyde, unstable, 6, 4, ethane, Clemmensen’s, 2, 3, carboxylic acid, high, propane, Rosenmund's]

The coordination number and oxidation state of the complex K4[Fe(CN6)] are ______ and ______ respectively.

Concept: Coordination Compounds - calculation for a complex coordination sphere
Chapter: [0.07] Coordination Compounds
[1]1.i.d

Fill in the blanks by choosing the appropriate words from those given in the brackets:

[stable, low, aldehyde, unstable, 6, 4, ethane, Clemmensen’s, 2, 3, carboxylic acid, high, propane, Rosenmund's]

Propanone on reaction with zinc amalgam in the presence of conc. HCI gives ______ and the reaction is known as ______ reduction.

Concept: Aldehydes and Ketones - Reduction to Alcohol and Alkanes
Chapter: [0.131] Carbonyl compounds
[4]1.ii
[1]1.ii.a

The reaction of a primary amine with chloroform and ethanolic KOH is called ______.

Carbylamine reaction

Kolbe's reaction

Reimer-Tiemann reaction

Wurtz-Fittig reaction

Concept: Amines - Chemical Reactions of Amines - Carbylamine Reaction
Chapter: [0.15] Cyanides, Isocyanides, Nitro compounds, Amines and Diazonium Salt
[1]1.ii.b

Which one of the following statements is true for the galvanic cell?

Electrons flow from the copper electrode to the zinc electrode.

Current flows from the zinc electrode to the copper electrode.

Cations move towards the copper electrode.

Cations move towards zinc electrode.

Concept: Galvanic Cells, Mechanism of Current Production in a Galvanic Cell; - Galvanic Cells - Introduction
Chapter: [0.062] Galvanic cells, mechanism of current production in a galvanic cell;
[1]1.ii.c

Which one of the following compounds is diamagnetic and colourless?

\[\ce{K2Cr2O7}\]

\[\ce{ZnSO4}\]

\[\ce{KMnO4}\]

\[\ce{Cr2(SO4)3}\]

Concept: Magnetic Properties
Chapter: [0.02] States of Matters: Structure and Properties Solid State
[1]1.ii.d

For a first order reaction, the half-life period (t1/2) is ______.

proportional to the initial concentration.

inversely proportional to the initial concentration.

proportional to the square root of the initial concentration.

independent of the initial concentration.

Concept: Order of a Reaction - Derivation of Expression of Half-life Period from First Order Rate Equation
Chapter: [0.0301] Order of a reaction
[4]1.iii

Match the following:

(i) Phenol (a) Hexane + heptane
(ii) EDTA (b) Globular protein
(iii) Ideal solution (c) Azo dye
(iv) Insulin (d) Hexadentate ligand
Concept: Phenols - Phenols
Chapter: [0.12300000000000001] Distinction between primary, secondary and tertiary alcohols
[2]1.iv
[1]1.iv.a

Assertion: If a solution contains both H+ and Na+ ions, the H+ ions are reduced first at cathode.

Reason: Cations with higher E° value are reduced first at cathode.

Both Assertion and reason are true and Reason is the correct explanation for Assertion.

Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion.

Assertion is true but Reason is false.

Assertion is false but Reason is true.

Concept: Ionic Equilibria - Multistage Ionization of Acids and Bases with Examples
Chapter: [0.052000000000000005] Ionic product of water, pH of solutions and pH indicators
[1]1.iv.b

Assertion: Addition of bromine water to 1-butene gives two optical isomers.

Reason: The product formed contains two asymmetric carbon atoms.

Both Assertion and Reason are true, and Reason is the correct explanation for Assertion.

Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion.

Assertion is true but Reason is false.

Assertion is false, but Reason is true.

Concept: Isomerism in Coordination Compounds - Stereoisomerism
Chapter: [0.07] Coordination Compounds
SECTION B - 20 MARKS
[2]2

Calculate the mass of ascorbic acid (molecular mass = 176 g/mol) that should be dissolved in 155 g of acetic acid to cause a depression of the freezing point by 1.15 K. Assume that ascorbic acid does not dissociate or associate in the solution. (Kf for acetic acid = 3.9 K kg/mol)

Concept: Relative Molecular Mass of Non-volatile Substances - Depression in Freezing Point
Chapter: [0.013000000000000001] Relative molecular mass of non-volatile substances
[2]3
[1]3.i

Give a reason for the following:

Cu+2 salts are paramagnetic, while Cu+ salts are diamagnetic.

Concept: Magnetic Properties
Chapter: [0.02] States of Matters: Structure and Properties Solid State
[1]3.ii

Give a reason for the following:

Mn+2 compounds are more stable than Fe+2 compounds.

Concept: Concept of Group 17 Elements
Chapter: [0.08] Chemistry of p-Block Elements: Group 16, 17, 18
[2]4
[1]4.i

Give a chemical equation for the following:

Ethyl chloride is treated with aqueous KOH solution.

Concept: Alcohol - Uses of Alcohols
Chapter: [0.121] Methods of preparation, manufacture, properties and use
[1]4.ii

Give a chemical equation for the following:

Chlorobenzene is treated with ammonia at 573 K and high pressure.

Concept: Chlorobenzene - Preparation from Aniline
Chapter: [0.114] Chlorobenzene
[2]5
[1]5.i

State one reason for the following:

Alkylamine is soluble in water, whereas arylamine is insoluble in water.

Concept: Amines - Chemical Reactions of Amines - Basic Character of Amines
Chapter: [0.15] Cyanides, Isocyanides, Nitro compounds, Amines and Diazonium Salt
[1]5.ii

State one reason for the following:

Methylamine is a stronger base than methyl alcohol.

Concept: Alcohol - Uses of Alcohols
Chapter: [0.121] Methods of preparation, manufacture, properties and use
[2]6

Calculate the emf of the following cell at 298 K.

\[\ce{Cu/Cu^{2+}_{(0.025 M)}//Ag^+_{(0.005 M)}/Ag}\]

Given `"E"_("Cu"^(2+)//"Cu")^circ` = 0.34 V, `"E"_("Ag"^+//"Ag")^circ` = 0.80 V

1 Faraday = 96500 C mol -1

Concept: Nernst Equation - Introduction
Chapter: [0.062] Galvanic cells, mechanism of current production in a galvanic cell;
[2]7
[1]7.i

Complete and balance the following chemical equation:

\[\ce{KMnO4 + KI + H2SO4 → }\]_____ + _____ + _____ + ______

Concept: Methods of Preparation and Manufacture of Alcohol - Manufacture of Methanol by Bosch Process and Ethanol by Fermentation of Carbohydrates
Chapter: [0.121] Methods of preparation, manufacture, properties and use
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[1]7.ii

Complete and balance the following chemical equation:

\[\ce{K2Cr2O7 + H2SO4 + H2S →}\]____ + ____ + ____ + ____

Concept: Methods of Preparation and Manufacture of Alcohol - Manufacture of Methanol by Bosch Process and Ethanol by Fermentation of Carbohydrates
Chapter: [0.121] Methods of preparation, manufacture, properties and use
[2]8
[2]8.i
[1]8.i.a

How will the following be obtained? (Give chemical equation):

Ethanol from Grignard's reagent.

Concept: Acid Derivatives - Reaction with Grignard Reagent
Chapter: [0.142] Acid derivatives
[1]8.i.b

How will the following be obtained? (Give chemical equation):

Diethyl ether from sodium ethoxide.

Concept: General Formula and Structure
Chapter: [0.132] Ethers
OR
[2]8.ii

An organic compound [A] C2H6O, on heating with conc. H2SO4 at 413 K gives a neutral compound [B] C4H10O. Compound [B] on treatment with PCl5 gives a product, which on subsequent treatment with KCN yields compound [C] C3H5N. Compound [C] on hydrolysis gives an acid [D] C3H6O2. Identify the compounds [A], [B], [C] and [D].

Concept: Acid Derivatives - Formation of Acid Derivatives
Chapter: [0.141] Carboxylic acids [0.142] Acid derivatives
[2]9

The osmotic pressure of blood at 37°C is 8.21 atm. How much glucose in grams should be used per litre of aqueous solution for an intravenous injection so that it is isotonic with blood? (Molecular wt of glucose = 180 g/mol)

Concept: Relative Molecular Mass of Non-volatile Substances - Osmotic Pressure and Its Application in the Determination of Relative Molecular Mass
Chapter: [0.013000000000000001] Relative molecular mass of non-volatile substances
[2]10

An aromatic carboxylic acid [A], which readily sublimes on heating, produces compound [B] on treatment with PCl5, Compound [B], when reduced in the presence of Pd catalyst over BaSO4 poisoned by sulphur in xylene solution, gives compound [C]. When compound [C] is condensed in the presence of alcoholic KCN, it gives compound [D] (Molecular formula of compound [D] is C14H12O2)

Identify the compounds [A], [B], [C] and [D].

Concept: Physical Properties of Carboxylic Acids
Chapter: [0.141] Carboxylic acids
[2]11
[1]11.i

State a reason for the following:

La(OH)3 is more basic than Lu(OH)3.

Concept: F-block Elements - The Lanthanoids
Chapter: [0.1] Chemistry of Transition and Inner-Transition Elements: d-Block: 3d, 4d and 5d series f-Block: 4f and 5f series
[1]11.ii

How would you account for the following? 

Transition metals and their compounds act as catalysts.

Concept: General Properties of the Transition Elements (D-block)
Chapter: [0.1] Chemistry of Transition and Inner-Transition Elements: d-Block: 3d, 4d and 5d series f-Block: 4f and 5f series
SECTION C - 21 MARKS
[3]12

20% of a first-order reaction is completed in five minutes. How much time will the 60% reaction take to complete? Calculate the half-life period (t1/2) for the above reaction.

Concept: Order of a Reaction - Problems Based on First Order Rate Equation and Half Life Period
Chapter: [0.0301] Order of a reaction
[3]13
[1]13.i

Write the balanced chemical equation for the following name reaction:

Sandmeyer's reaction

Concept: Aniline - Sandmeyer’s Reaction
Chapter: [0.15] Cyanides, Isocyanides, Nitro compounds, Amines and Diazonium Salt
[1]13.ii

Write the balanced chemical equation for the following name reaction:

Wurtz reaction

Concept: Chlorobenzene - Wurtz-fittig Reaction
Chapter: [0.114] Chlorobenzene
[1]13.iii

Write the balanced chemical equation for the following name reaction:

Finkelstein reaction

Concept: Preparation, Properties, and Uses of the Following: Ethyl Bromide, Chloroform, Iodoform, Haloform Reaction
Chapter: [0.115] Preparation, properties, and uses of the following
[3]14
[1]14.i

Give an example of reducing sugar.

Concept: Carbohydrates classification
Chapter: [0.17] Biomolecules – carbohydrates, proteins, enzymes, vitamins and nucleic acids

Give an example of non-reducing sugar.

Concept: Carbohydrates classification
Chapter: [0.17] Biomolecules – carbohydrates, proteins, enzymes, vitamins and nucleic acids
[1]14.ii

What is denaturation of proteins?

Concept: Proteins - Denaturation of Proteins
Chapter: [0.17] Biomolecules – carbohydrates, proteins, enzymes, vitamins and nucleic acids
[1]14.iii

Give an example of water soluble vitamin.

Concept: Introduction of Vitamins
Chapter: [0.17] Biomolecules – carbohydrates, proteins, enzymes, vitamins and nucleic acids

Give an example of fat soluble vitamin.

Concept: Introduction of Vitamins
Chapter: [0.17] Biomolecules – carbohydrates, proteins, enzymes, vitamins and nucleic acids
[3]15

When 2 g of benzoic acid is dissolved in 25 g of benzene, it shows a depression in freezing point equal to 1.62 K. The molal depression constant (Kf) of benzene is 4.9 K kg mol-1, and the molecular weight of benzoic acid is 122 g/mol. What will be the percentage association of the benzoic acid?

(Benzoic acid forms dimers when dissolved in benzene.)

Concept: Relative Molecular Mass of Non-volatile Substances - Freezing Point Depression
Chapter: [0.013000000000000001] Relative molecular mass of non-volatile substances
[3]16
[1]16.i

Account for the following:

Phenol is a stronger acid than aliphatic alcohol.

Concept: Phenols - Phenols
Chapter: [0.12300000000000001] Distinction between primary, secondary and tertiary alcohols
[1]16.ii

Account for the following:

Ethanol gives iodoform reaction whereas methanol does not give iodoform reaction.

Concept: Aldehydes and Ketones - Iodoform Reaction
Chapter: [0.131] Carbonyl compounds
[1]16.iii

Account for the following:

Ethers should not be distilled to dryness.

Concept: Ethers - Preparation of Ethers
Chapter: [0.132] Ethers
[3]17
[3]17.i
[1.5]17.i.a

Identify the compounds [A], [B] and [C] in the following reaction:

\[\ce{CH3COOH ->[NH3][\Delta] [A] ->[Br2 + KOH] [B] ->[CHCl3 + NaOH_{(alc)}] [C]}\]

Concept: Isocyanides - Methods of Preparation Isocyanides from Alkyl Halide
Chapter: [0.15] Cyanides, Isocyanides, Nitro compounds, Amines and Diazonium Salt
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[1.5]17.i.b

Identify the compounds [A], [B] and [C] in the following reaction:

\[\ce{CH3Br ->[KCN] [A] ->[LiAlH_4] [B] ->[HNO2][273 K] [C]}\]

Concept: Cyanides - Methods of Preparation: Cyanides from Alkyl Halide
Chapter: [0.15] Cyanides, Isocyanides, Nitro compounds, Amines and Diazonium Salt
OR
[3]17.ii
[1]17.ii.a

How will the following be converted? (Give chemical equation)

Ethyl bromide to ethyl isocyanide

Concept: Isocyanides - Methods of Preparation Isocyanides from Alkyl Halide
Chapter: [0.15] Cyanides, Isocyanides, Nitro compounds, Amines and Diazonium Salt
[1]17.ii.b

How will the following be converted? (Give chemical equation)

Aniline to benzene diazonium chloride.

Concept: Diazonium Salts - Method of Preparation of Diazonium Salts
Chapter: [0.15] Cyanides, Isocyanides, Nitro compounds, Amines and Diazonium Salt
[1]17.ii.c

How will the following be converted? (Give chemical equation)

Benzene diazonium chloride to phenol

Concept: Phenols - Preparation of Phenol from Diazonium Salt
Chapter: [0.12300000000000001] Distinction between primary, secondary and tertiary alcohols
[8]18

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)

Concept: Temperature Dependence of the Rate of a Reaction
Chapter: [0.0305] The concept of energy
SECTION D - 15 MARKS
[5]19
[3]19.i
[1]19.i.a

Write a chemical equation to illustrate the following name reaction:

Cannizzaro’s reaction.

Concept: Aldehydes and Ketones - Base Catalysed Reactions
Chapter: [0.131] Carbonyl compounds
[1]19.i.b

Write a chemical equation to illustrate the following name reaction:

HVZ reaction

Concept: Acids - HVZ Reactions
Chapter: [0.141] Carboxylic acids
[1]19.i.c

Write a chemical equation to illustrate the following name reaction:

Aldol condensation.

Concept: Aldehydes and Ketones - Base Catalysed Reactions
Chapter: [0.131] Carbonyl compounds
[2]19.ii
[1]19.ii.a

How will the following be converted? (Give chemical equation)

Acetaldehyde to acetone

Concept: Aldehydes and Ketones - Difference Between Formaldehyde and Acetaldehyde
Chapter: [0.131] Carbonyl compounds
[1]19.ii.b

How will you bring about the following conversion? (Give equation).

Formaldehyde to urotropine

Concept: Aldehydes and Ketones - Difference Between Formaldehyde and Acetaldehyde
Chapter: [0.131] Carbonyl compounds
[5]20
[3]20.i
[1]20.i.a

Name the type of isomerism exhibited by the following pair of compound:

\[\ce{[Co(NH3)5 [ONO]Cl2  and  [Co(NH3)5(NO2)]Cl2}\]

Concept: Isomerism in Coordination Compounds
Chapter: [0.07] Coordination Compounds
[1]20.i.b

Name the type of isomerism exhibited by the following pair of compound:

\[\ce{[Cr(H2O)5Cl]Cl2H2O  and  [Cr(H2O)4Cl2]Cl {.} 2H2O}\]

Concept: Isomerism in Coordination Compounds
Chapter: [0.07] Coordination Compounds
[1]20.i.c

Name the type of isomerism exhibited by the following pair of compound:

\[\ce{[Pt(NH3)4Cl2]Br2  and  [Pt(NH3)4 Br2]Cl2}\]

Concept: Isomerism in Coordination Compounds
Chapter: [0.07] Coordination Compounds
[2]20.ii
[1]20.ii.a

Write the IUPAC name of the following complex:

\[\ce{[Co(NH3)4(H2O)2]Cl3}\]

Concept: Coordination Compounds - IUPAC rules of nomenclature of coordination compounds
Chapter: [0.07] Coordination Compounds
[1]20.ii.b

Write the IUPAC name of the following complex:

\[\ce{K2[Ni(CN4)]}\]

Concept: Coordination Compounds - IUPAC rules of nomenclature of coordination compounds
Chapter: [0.07] Coordination Compounds
[5]21
[5]21.i
[2.5]21.i.a

The specific conductance of 2.5 × 10-4 M formic acid is 5.25 × 10-5 ohm-1 cm-1. Calculate its molar conductivity and degree of dissociation.

Given `λ°_("H"^+)` = 349.5 ohm-1 cm2 mol-1 and

`λ°_("HCOO"^-)  = 50.5 " ohm"^-1 "cm"^2  "mol"^-1`

Concept: Conductance of Electrolytic Solutions - Variation of Conductivity and Molar Conductivity with Concentration
Chapter: [0.064] Electrolytic conductance
[2.5]21.i.b

Calculate the time taken to deposit 1.27 g at copper at cathode when a current of 2 amp. is passed through the solution of CuSO4.

(Atomic weight of Cu = 63.5 gmol-1)

Concept: Applications of Electrolysis - Faraday’S Laws of Electrolysis
Chapter: [0.061] Faraday’s laws of Electrolysis, Coulometer
OR
[5]21.ii
[2.5]21.ii.a

The resistance of a conductivity cell with a 0.1 M KCl solution is 200 ohm. When the same cell is filled with a 0.02 M NaCl solution, the resistance is 1100 ohm. If the conductivity of 0.1 M KCl solution is 0.0129 ohm-1 cm-1, calculate the cell constant and molar conductivity of 0.02 M NaCl solution.

Concept: Conductance of Electrolytic Solutions - Variation of Conductivity and Molar Conductivity with Concentration
Chapter: [0.064] Electrolytic conductance
[2.5]21.ii.b

The emf \[\ce{E^\circ_\text{cell}}\] of the following reaction is 0.89 V.

\[\ce{3Sn^{4+} + 2Cr -> 3Sn^{2+} + 2Cr^{1+}}\]

Calculate the value of ΔG° for the reaction. Predict whether the above reaction will be spontaneous or not.

Concept: Galvanic Cells, Mechanism of Current Production in a Galvanic Cell; - Galvanic Cells - Introduction
Chapter: [0.062] Galvanic cells, mechanism of current production in a galvanic cell;

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