Chemistry · 2020 · Set 56/3/1

CBSE Class 12 Chemistry 2020 — Set 56/3/1

CBSE Class XII Board 2020 · Set 56/3/1

Real board examination⚠ Old pattern · pre-2020 syllabus

Sets

About the 2020 exam: The 2020 exam used CBSE's older pattern — 37 questions for 70 marks, with no case studies. All three series (56/1/1, 56/2/1, 56/3/1) are here in full (37/37), each verified against the official CBSE paper. Several topics examined in 2020 were removed from today's syllabus — those questions are badged and filterable above.

This paper has 9 questions on a topic removed in CBSE’s 2023-24 syllabus update (each marked Not in syllabus). It’s kept for historical accuracy — the exam really asked it that year — but isn’t in the current syllabus and doesn’t count toward a concept’s importance. Switch to to focus on what’s still examinable.

About this paper

The real Class-12 board examination held in 2020. Every question below is solved the concept-first way. Sample papers are labelled honestly — never shown as a past exam.

Total marks: 70
Questions: 37
Duration: 180 min
Sections: 4

The marks / questions / duration above are the official exam pattern. We currently have 37 of this paper’s questions (100% of the full paper), with 37 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	Very short answer (incl. passage-based + one-word)	20	1	20
BSection B	Short answer	7	2	14
CSection C	Long answer type-I	7	3	21
DSection D	Long answer type-II	3	5	15
Total		37		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 2020 · Set 56/3/1

Series/Set: 56/3/1Roll No. ________

Time Allowed: 3 hoursMaximum Marks: 70

General Instructions

This question paper contains 37 questions divided into 4 sections — A, B, C, D.
Section A comprises 20 questions of 1 mark each (Very short answer (incl. passage-based + one-word)).
Section B comprises 7 questions of 2 marks each (Short answer).
Section C comprises 7 questions of 3 marks each (Long answer type-I).
Section D comprises 3 questions of 5 marks each (Long answer type-II).

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

Section A

Very short answer (incl. passage-based + one-word) · 1 mark each · 20 of 20 shown

Q1.

Read the given passage and answer the questions number 1 to 5 that follow: The d-block of the periodic table contains the elements of the groups 3-12 and are known as transition elements. In general, the electronic configuration of these elements is

(n-1)d^{1-10}\,ns^{1-2}

. The d-orbitals of the penultimate energy level in their atoms receive electrons giving rise to the three rows of the transition metals i.e., 3d, 4d and 5d series. However, Zn, Cd and Hg are not regarded as transition elements. Transition elements exhibit certain characteristic properties like variable oxidation states, complex formation, formation of coloured ions and alloys, catalytic activity, etc. Transition metals are hard (except Zn, Cd and Hg) and have a high melting point. Why are Zn, Cd and Hg non-transition elements?

[1]

Q2.

Which transition metal of 3d series does not show variable oxidation states?

[1]

Q3.

Why do transition metals and their compounds show catalytic activity?

[1]

Q4.

Why are melting points of transition metals high?

[1]

Q5.

Why is

Cu^{2+}

ion coloured while

Zn^{2+}

ion is colourless in aqueous solution?

[1]

Q6.

Name the cell which was used in the Apollo Space Programme.

[1]

Page 1 of 6

Q7.

How many coulombs are required for the oxidation of 1 mol of H₂O to O₂?

[1]

Q8.

Write the slope value obtained in the plot of ln[R] vs. time for a first order reaction.

[1]

Q9.

Name the disaccharide which on hydrolysis gives two molecules of glucose.

[1]

Q10.

Name the class of the synthetic detergent which is used in toothpaste.

⚠ This question is not in the current syllabus — Chemistry in Everyday Life (removed 2023-24)

[1]

Q11.

Which of the following is refined by the zone refining process? (A) Cu (B) Zn (C) Ge (D) Sn

⚠ This question is not in the current syllabus — General Principles and Processes of Isolation of Elements (removed 2023-24)

[1]

Q12.

Racemisation occurs in (A) SN2 reaction (B) SN1 reaction (C) Neither SN2 nor SN1 reactions (D) SN2 reaction as well as SN1 reaction

[1]

Q13.

C₆H₅CH₂NH₂ (benzylamine) on heating with CHCl₃ and alcoholic KOH gives foul smell of (A) C₆H₅CH₂OH (B) C₆H₅CH₂NC (C) C₆H₅CH₂CN (D) C₆H₅CH₂Cl

[1]

Q14.

One mole of CrCl₃ · 6H₂O compound reacts with excess AgNO₃ solution to yield two moles of AgCl (s). The structural formula of the compound is (A) [Cr(H₂O)₅Cl]Cl₂ · H₂O (B) [Cr(H₂O)₃Cl₃] · 3H₂O (C) [Cr(H₂O)₄Cl₂]Cl · 2H₂O (D) [Cr(H₂O)₆]Cl₃

[1]

Q15.

Peptide linkage is present in (A) Carbohydrates (B) Vitamins (C) Proteins (D) Rubber

[1]

Q16.

Assertion (A) : Conductivity of an electrolyte decreases with decrease in concentration. Reason (R) : Number of ions per unit volume increases on dilution. (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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Q17.

Assertion (A) : The C - O - H bond angle in alcohols is slightly less than the tetrahedral angle. Reason (R) : This is due to the repulsive interaction between the two lone electron pairs on oxygen. (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) : [Pt(en)₂Cl₂]²⁺ complex is less stable than [Pt(NH₃)₄Cl₂]²⁺ complex. Reason (R) : [Pt(en)₂Cl₂]²⁺ complex shows chelate effect. (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]

Q19.

Assertion (A) : Osmotic pressure is a colligative property. Reason (R) : Osmotic pressure is directly proportional to molarity. (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]

Q20.

Assertion (A) : Reactivity of ketones is more than aldehydes. Reason (R) : The carbonyl carbon of ketones is less electrophilic as compared to aldehydes. (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

Short answer · 2 marks each · 7 of 7 shown

Q1.

In the given reaction A + 3B arrow 2C, the rate of formation of C is 2.5 × 10⁻⁴ mol L⁻¹s⁻¹. Calculate the (i) rate of reaction, and (ii) rate of disappearance of B.

[2]

Q2.

Write the role of the following: (i) NaAlF₄ in the extraction of Aluminium (ii) CO in the refining of Ni OR Write the chemical equations involved in the leaching of bauxite ore to prepare pure alumina.

⚠ This question is not in the current syllabus — General Principles and Processes of Isolation of Elements (removed 2023-24)

[2]

Q3.

Write two differences between physisorption and chemisorption. OR Define the following terms with a suitable example of each: (i) Associated colloids (ii) O/W emulsion

⚠ This question is not in the current syllabus — Surface Chemistry (removed 2023-24)

[2]

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Q4.

(a) Write the IUPAC name and hybridisation of the complex [CoF₆]³⁻. (Given: Atomic number of Co = 27) (b) What type of isomerism is shown by the complex [Co(en)₂Cl₂]²⁺? Name the structure of an isomer of this complex which is optically active.

[2]

Q5.

Give reasons: (i) Shaving soaps contain glycerol. (ii) Antacids should not be used for longer time.

⚠ This question is not in the current syllabus — Chemistry in Everyday Life (removed 2023-24)

[2]

Q6.

Define the following terms: (i) Oligosaccharides (ii) Invert sugar

[2]

Q7.

Write the products of the following reaction: 6XeF₄ + 12H₂O arrow Is this reaction a disproportionation reaction? Give reasons in support of your answer.

⚠ This question is not in the current syllabus — The p-Block Elements (removed 2023-24)

[2]

Section C

Long answer type-I · 3 marks each · 7 of 7 shown

Q1.

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 = 96500 C mol⁻¹

[3]

Q2.

A first order reaction is 40% complete in 80 minutes. Calculate the value of rate constant (k). In what time will the reaction be 90% completed? [Given: log 2 = 0.3010, log 3 = 0.4771, log 4 = 0.6021, log 5 = 0.6771, log 6 = 0.7782]

[3]

Q3.

Write the names and structures of the monomers in the following polymers: (i) Buna-S (ii) Nylon-6,6 (iii) Bakelite

⚠ This question is not in the current syllabus — Polymers (removed 2023-24)

[3]

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Q4.

Write the major product(s) of the following reactions: (i) C₆H₅Cl (chlorobenzene) xrightarrow[Δ]Conc. H₂SO₄ (ii) 4-hydroxybenzyl alcohol, HOCH₂-C₆H₄-OH (para-substituted benzene) xrightarrow[Δ]HCl (iii) (CH₃)₃C-OH xrightarrowCu,573K

[3]

Q5.

(a) Write the mechanism of the following reaction: 2CH₃CH₂OH xrightarrow[413K]H^+ CH₃CH₂OCH₂CH₃ + H₂O (b) Write the preparation of phenol from cumene. OR How can you convert the following: (i) Sodium phenoxide to o-hydroxybenzoic acid (ii) Acetone to propene (iii) Phenol to chlorobenzene

[3]

Q6.

Write the products formed when (CH₃)₃C-CHO reacts with the following reagents: (i) CH₃COCH₃ in the presence of dilute NaOH (ii) HCN (iii) Conc. NaOH

[3]

Q7.

Define Lyophobic and Lyophilic sol with a suitable example of each. Why is coagulation of Lyophilic sol difficult as compared to Lyophobic sol? OR Define the following terms: (i) Shape-selective catalysis (ii) Kraft temperature (iii) Peptization

⚠ This question is not in the current syllabus — Surface Chemistry (removed 2023-24)

[3]

Section D

Long answer type-II · 5 marks each · 3 of 3 shown

Q1.

(a) Give reasons: (i) Helium does not form compounds like Xenon. (ii) HClO₄ is a stronger acid than HOCl. (iii) Sulphur is a polyatomic solid whereas Oxygen is a diatomic gas. (b) Write one reaction as an example of each, to show that conc. H₂SO₄ acts as (i) an oxidising agent, and (ii) a dehydrating agent. OR (a) Account for the following: (i) Hydration enthalpy of F^- ion is more than Cl^- ion. (ii) SO₂ is a reducing agent, whereas TeO₂ is an oxidising agent in group-16 oxides. (b) Write the reaction of F₂ with water. Why does I₂ not react with water? (c) Draw the structure of XeF₂.

⚠ This question is not in the current syllabus — The p-Block Elements (removed 2023-24)

[5]

Page 5 of 6

Q2.

(a) Give reasons: (i) Although -NH₂ group is o/p directing in electrophilic substitution reactions, yet aniline, on nitration gives good yield of m-nitroaniline. (ii) (CH₃)₂NH is more basic than (CH₃)₃N in an aqueous solution. (iii) Ammonolysis of alkyl halides is not a good method to prepare pure primary amines. (b) Distinguish between the following: (i) CH₃CH₂NH₂ and (CH₃CH₂)₂NH (ii) Aniline and CH₃NH₂ OR (a) Write the structures of A and B in the following reactions: (i) C₆H₅overset+N₂Cl^- xrightarrowCuCN A xrightarrowH^+/H₂O B (ii) CH₃COOH xrightarrowNH₃ A xrightarrowNaOBr B (b) Write the chemical reaction of methyl amine with benzoyl chloride and write the IUPAC name of the product obtained. (c) Arrange the following in the increasing order of their pKb values: C₆H₅NH₂, NH₃, C₂H₅NH₂, (C₂H₅)₂NH

[5]

Q3.

(a) A solution contains 5.85 g NaCl (Molar mass = 58.5 g mol⁻¹) per litre of solution. It has an osmotic pressure of 4.75 atm at 27 °C. Calculate the degree of dissociation of NaCl in this solution. (Given: R = 0.082 L atm K⁻¹mol⁻¹) (b) State Henry's law. Why is air diluted with helium in the tanks used by scuba divers? OR (a) When 19.5 g of F-CH₂-COOH (Molar mass = 78 g mol⁻¹) is dissolved in 500 g of water, the depression in freezing point is observed to be 1 °C. Calculate the degree of dissociation of F-CH₂-COOH. [Given: Kf for water = 1.86 K kg mol⁻¹] (b) Give reasons: (i) 0.1 M KCl has higher boiling point than 0.1 M Glucose. (ii) Meat is preserved for a longer time by salting.

[5]

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