Chemistry · 2023 · Set 56/1/1

CBSE Class 12 Chemistry 2023 — Set 56/1/1

CBSE Class XII Board 2023 · Set 56/1/1

Real board examination

Sets

About this paper

The real Class-12 board examination held in 2023. Every question below is solved the concept-first way. Sample papers are labelled honestly — never shown as a past exam.

Total marks: 70
Questions: 35
Duration: 180 min
Sections: 5

The marks / questions / duration above are the official exam pattern. We currently have 35 of this paper’s questions (100% of the full paper), with 35 fully solved. Questions we couldn’t yet extract or verify are held — never shown as complete.

Sections & marks

Section	Type	Questions	Marks each	Total
ASection A	MCQ	18	1	18
BSection B	Very short answer	7	2	14
CSection C	Short answer	5	3	15
DSection D	Case-based	2	4	8
ESection E	Long answer	3	5	15
Total		35		70

The question paper

The questions we hold for this paper, laid out by section. Solutions are on the Answers tab.

Board Examination

Chemistry

CBSE Class XII Board 2023 · Set 56/1/1

Series/Set: 56/1/1Roll No. ________

Time Allowed: 3 hoursMaximum Marks: 70

General Instructions

This question paper contains 35 questions divided into 5 sections — A, B, C, D, E.
Section A comprises 18 questions of 1 mark each (MCQ).
Section B comprises 7 questions of 2 marks each (Very short answer).
Section C comprises 5 questions of 3 marks each (Short answer).
Section D comprises 2 questions of 4 marks each (Case-based).
Section E comprises 3 questions of 5 marks each (Long answer).

Above is the official exam pattern. The questions printed below are those we currently hold for this paper.

Section A

MCQ · 1 mark each · 18 of 18 shown

Q1.

The colligative property used for the determination of molar mass of polymers and proteins is : (A) Osmotic pressure (B) Depression in freezing point (C) Relative lowering in vapour pressure (D) Elevation in boiling point

[1]

Q2.

Low concentration of oxygen in the blood and tissues of people living at high altitude is due to : (A) high atmospheric pressure (B) low temperature (C) low atmospheric pressure (D) both low temperature and high atmospheric pressure

[1]

Q3.

The correct cell to represent the following reaction is :

Zn + 2Ag^+ \rightarrow Zn^{2+} + 2Ag

(A)

2Ag | Ag^+ || Zn | Zn^{2+}

(B)

Ag^+ | Ag || Zn^{2+} | Zn

(C)

Ag | Ag^+ || Zn | Zn^{2+}

(D)

Zn | Zn^{2+} || Ag^+ | Ag

[1]

Q4.

\Delta G

and

E^\circ_{cell}

for a spontaneous reaction will be : (A) positive, negative (B) negative, negative (C) negative, positive (D) positive, positive

[1]

Q5.

Which of the following is affected by catalyst ? (A)

\Delta H

(B)

\Delta G

(C)

E_a

(D)

\Delta S

[1]

Q6.

The order of the reaction $H_2

(g) + Cl_2
(g) \rightarrow 2HCl (g)$ is : (A) 2 (B) 1 (C) 0 (D) 3

[1]

Page 1 of 6

Q7.

The most common and stable oxidation state of a Lanthanoid is : (A) + 2 (B) + 3 (C) + 4 (D) + 6

[1]

Q8.

The compounds [Co(SO₄)(NH₃)₅]Br and [Co(Br)(NH₃)₅]SO₄ represent : (A) optical isomerism (B) linkage isomerism (C) ionisation isomerism (D) coordination isomerism

[1]

Q9.

The synthesis of alkyl fluoride is best obtained from : (A) Free radicals (B) Swartz reaction (C) Sandmeyer reaction (D) Finkelstein reaction

[1]

Q10.

In the reaction R-OH + HCl xrightarrowZnCl₂ RCl + H₂O, what is the correct order of reactivity of alcohol ? (A) 1^° < 2^° < 3^° (B) 1^° > 3^° > 2^° (C) 1^° > 2^° > 3^° (D) 3^° > 1^° > 2^°

[1]

Q11.

CH₃CONH₂ on reaction with NaOH and Br₂ in alcoholic medium gives : (A) CH₃COONa (B) CH₃NH₂ (C) CH₃CH₂Br (D) CH₃CH₂NH₂

[1]

Q12.

Which of the following is least basic ? (A) (CH₃)₂NH (B) NH₃ (C) Aniline, C₆H₅NH₂ (benzene ring bearing -NH₂, drawn as a structure in the paper) (D) (CH₃)₃N

[1]

Q13.

The glycosidic linkage involved in linking the glucose units in amylose part of starch is : (A) α-C₁-C₆ linkage (B) β-C₁-C₆ linkage (C) α-C₁-C₄ linkage (D) β-C₁-C₄ linkage

[1]

Q14.

An α-helix is a structural feature of : (A) Sucrose (B) Starch (C) Polypeptides (D) Nucleotides

[1]

Q15.

Assertion (A) : -NH₂ group is o- and p-directing in electrophilic substitution reactions. Reason (R) : Aniline cannot undergo Friedel-Crafts reaction. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.

[1]

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Q16.

Assertion (A) : Acetylation of aniline gives a monosubstituted product. Reason (R) : Activating effect of -NHCOCH₃ group is more than that of amino group. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.

[1]

Q17.

Assertion (A) : The molecularity of the reaction H₂ + Br₂ arrow 2HBr appears to be 2. Reason (R) : Two molecules of the reactants are involved in the given elementary reaction. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.

[1]

Q18.

Assertion (A) : Low spin tetrahedral complexes are rarely observed. Reason (R) : Crystal field splitting energy is less than pairing energy for tetrahedral complexes. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true.

[1]

Section B

Very short answer · 2 marks each · 7 of 7 shown

Q1.

State Henry's law. Give one application of it.

[2]

Q2.

(a) On diluting two electrolytes A and B, the molar conductivity of A increases 25 times while that of B increases 1.5 times. Which of the two electrolytes is strong ? Justify your answer graphically. OR (b) The electrical resistance of a column of 0.05molL⁻¹ NaOH solution of diameter 1 cm and length 50 cm is 5.55 × 10³ ohm. Calculate the conductivity.

[2]

Q3.

Complete the following equations : (a) 2MnO₄^- + 5NO₂^- + 6H^+ arrow (b) Cr₂O₇²⁻ + 14H^+ + 6e^- arrow

[2]

Q4.

Identify A and B in the following reactions : (a) CH₃-CH(OH)-CH₃ xrightarrowPCl₅ A xrightarrowAgCN B (b) CH₃CH₂CH₂Cl xrightarrow[ethanol]KOH A xrightarrowHBr B

[2]

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Q5.

(a) Account for the following : (i) Phenol is a stronger acid than an alcohol. (ii) The boiling point of alcohols decreases with increase in branching of alkyl chain. OR (b) (i) Write the mechanism of the following reaction : CH₃CH₂OH xrightarrow[443K]H^+ CH₂=CH₂ + H₂O (ii) Write the equation involved in Reimer-Tiemann reaction.

[2]

Q6.

Explain briefly : (a) Carbylamine reaction (b) Gabriel phthalimide synthesis

[2]

Q7.

(a) Write chemical reaction to show that open structure of D-glucose contains the straight chain. (b) What type of linkage is responsible for the formation of protein ?

[2]

Section C

Short answer · 3 marks each · 5 of 5 shown

Q1.

(a) Differentiate between Ideal solution and Non-ideal solution. (b) 30 g of urea is dissolved in 846 g of water. Calculate the vapour pressure of water for this solution if vapour pressure of pure water at 298 K is 23.8 mm Hg.

[3]

Q2.

Write main product formed when : (a) Methyl chloride is treated with NaI/Acetone. (b) 2,4,6-trinitrochlorobenzene is subjected to hydrolysis. (c) n-Butyl chloride is treated with alcoholic KOH.

[3]

Q3.

How do you convert the following : (Any three) (a) Phenol to picric acid (b) Propanone to 2-Methylpropan-2-ol (c) Phenol to anisole (d) Propene to Propan-1-ol

[3]

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Q4.

(a) Explain why : (i) Carboxyl group in benzoic acid is meta directing. (ii) Sodium bisulphite is used for the purification of aldehydes and ketones. (iii) Carboxylic acids do not give characteristic reactions of carbonyl group. OR (b) An organic compound 'A' with molecular formula C₃H₈O on reaction with Cu at 573 K gives 'B'. 'B' does not reduce Fehling's solution but gives a yellow precipitate of compound 'C' with I₂/NaOH. Deduce the structures of A, B and C.

[3]

Q5.

(a) What are the hydrolysis products of (i) Lactose, (ii) Maltose ? (b) Give the basic structural difference between starch and cellulose.

[3]

Section D

Case-based · 4 marks each · 2 of 2 shown

Q1.

The rate of reaction is concerned with decrease in concentration of reactants or increase in the concentration of products per unit time. It can be expressed as instantaneous rate at a particular instant of time and average rate over a large interval of time. Mathematical representation of rate of reaction is given by rate law. Rate constant and order of a reaction can be determined from rate law or its integrated rate equation. (i) What is average rate of reaction ? (ii) Write two factors that affect the rate of reaction. (iii) (1) What happens to rate of reaction for zero order reaction ? (2) What is the unit of k for zero order reaction ? OR (iii) (1) For a reaction P + 2Q arrow Products, Rate = k[P]1/2[Q]¹. What is the order of the reaction ? (2) Define pseudo first order reaction with an example.

[4]

Q2.

In coordination compounds, metals show two types of linkages, primary and secondary. Primary valencies are ionisable and are satisfied by negatively charged ions. Secondary valencies are non-ionisable and are satisfied by neutral or negative ions having lone pair of electrons. Primary valencies are non-directional while secondary valencies decide the shape of the complexes. (i) If PtCl₂ · 2NH₃ does not react with AgNO₃, what will be its formula ? (ii) What is the secondary valency of [Co(en)₃]³⁺ ? (iii) (1) Write the formula of Iron(III) hexacyanidoferrate(II). (2) Write the IUPAC name of [Co(NH₃)₅Cl]Cl₂. OR (iii) Write the hybridization and magnetic behaviour of [Ni(CN)₄]²⁻. [Atomic number : Ni = 28]

[4]

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Section E

Long answer · 5 marks each · 3 of 3 shown

Q1.

(a) (i) State Kohlrausch law of independent migration of ions. Write an expression for the limiting molar conductivity of acetic acid (CH₃COOH). (ii) Calculate the maximum work and log Kc for the given reaction at 298 K : Ni (s) + 2Ag^+ (aq) arrow Ni²⁺ (aq) + 2Ag (s) Given : E^°Ni²⁺/Ni = -0.25 V, E^°Ag^+/Ag = +0.80 V, 1F = 96500Cmol⁻¹ OR (b) (i) State Faraday's first law of electrolysis. How much charge, in terms of Faraday, is required for the reduction of 1 mol Cu²⁺ to Cu ? (ii) Calculate emf of the following cell at 298 K : Mg (s) | Mg²⁺ (0.1M) || Cu²⁺ (0.01M) | Cu (s) [E^°cell = +2.71 V, 1F = 96500Cmol⁻¹, log 10 = 1]

[5]

Q2.

Assign reason for each of the following : (i) Manganese exhibits the highest oxidation state of +7 among the 3d series of transition elements. (ii) Transition metals and their compounds are generally found to be good catalysts in chemical reactions. (iii) Cr²⁺ is reducing in nature while with the same d-orbital configuration (d⁴) Mn³⁺ is an oxidising agent. (iv) Zn has lowest enthalpy of atomization. (v) Cu^+ is unstable in an aqueous solution.

[5]

Q3.

(a) (i) Carry out the following conversions : (1) Ethanal to But-2-en-1-al (2) Propanoic acid to 2-chloropropanoic acid (ii) An alkene with molecular formula C₅H₁₀ on ozonolysis gives a mixture of two compounds 'B' and 'C'. Compound 'B' gives positive Fehling test and also reacts with iodine and NaOH solution. Compound 'C' does not give Fehling solution test but forms iodoform. Identify the compounds 'A', 'B' and 'C'. OR (b) (i) Distinguish with a suitable chemical test : (1) CH₃COCH₂CH₃ and CH₃CH₂CH₂CHO (2) Ethanal and Ethanoic acid (ii) Write the structure of oxime of acetone. (iii) Identify A to D : CH₃COOH xrightarrowPCl₅ A xrightarrowH₂/Pd-BaSO₄ B xrightarrow[(ii)H₃O^+](i)CH₃MgBr C xrightarrowLiAlH₄ D

[5]

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