Chemistry · 2020

CBSE Class 12 Chemistry 2020 — Previous-Year Question Paper

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

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 11 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 56/1/1

Series/Set: 56/1/1Roll 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 that follow: The substitution reaction of alkyl halide mainly occurs by SN1 or SN2 mechanism. Whatever mechanism alkyl halides follow for the substitution reaction to occur, the polarity of the carbon halogen bond is responsible for these substitution reactions. The rate of SN1 reactions are governed by the stability of carbocation whereas for SN2 reactions steric factor is the deciding factor. If the starting material is a chiral compound, we may end up with an inverted product or racemic mixture depending upon the type of mechanism followed by alkyl halide. Cleavage of ethers with HI is also governed by steric factor and stability of carbocation, which indicates that in organic chemistry, these two major factors help us in deciding the kind of product formed. Predict the stereochemistry of the product formed if an optically active alkyl halide undergoes substitution reaction by SN1 mechanism.

[1]

Q2.

Name the instrument used for measuring the angle by which the plane polarised light is rotated.

[1]

Q3.

Predict the major product formed when 2-Bromopentane reacts with alcoholic KOH.

[1]

Q4.

Give one use of

CHI_3

[1]

Q5.

Write the structures of the products formed when anisole is treated with HI.

[1]

Q6.

Identify which liquid will have a higher vapour pressure at

90\,°C

if the boiling points of two liquids A and B are

140\,°C

and

180\,°C

, respectively.

[1]

Page 1 of 6

Q7.

Out of zinc and tin, whose coating is better to protect iron objects?

[1]

Q8.

Will the rate constant of the reaction depend upon T if the Eact (activation energy) of the reaction is zero?

[1]

Q9.

Give the structure of the monomer of PVC.

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

[1]

Q10.

Which structural unit present in a detergent makes it non-biodegradable?

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

[1]

Q11.

Out of the following, the strongest base in aqueous solution is (A) Methylamine (B) Dimethylamine (C) Trimethylamine (D) Aniline

[1]

Q12.

Iodoform test is not given by (A) Ethanol (B) Ethanal (C) Pentan-2-one (D) Pentan-3-one

[1]

Q13.

Out of the following transition elements, the maximum number of oxidation states are shown by (A) Sc (Z = 21) (B) Cr (Z = 24) (C) Mn (Z = 25) (D) Fe (Z = 26)

[1]

Q14.

Hardening of leather in tanning industry is based on (A) Electrophoresis (B) Electro-osmosis (C) Mutual coagulation (D) Tyndall effect

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

[1]

Q15.

What is the correct IUPAC name of the given compound? c CH₃ ; | ; CH₃-C-CH₂-CH₃ ; | ; COOH (A) 2,2-Dimethylbutanoic acid (B) 2-Carboxyl-2-methylbutane (C) 2-Ethyl-2-methylpropanoic acid (D) 3-Methylbutane carboxylic acid

[1]

Q16.

Assertion (A) : Au and Ag are extracted by leaching their ores with a dil. solution of NaCN. Reason (R) : Impurities associated with these ores dissolve in NaCN. (A) Both Assertion (A) and Reason (R) are correct statements, and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are correct statements, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is correct, but Reason (R) is incorrect statement. (D) Assertion (A) is incorrect, but Reason (R) is correct statement.

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

[1]

Page 2 of 6

Q17.

Assertion (A) : F – F bond in F₂ molecule is weak. Reason (R) : F atom is small in size. (A) Both Assertion (A) and Reason (R) are correct statements, and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are correct statements, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is correct, but Reason (R) is incorrect statement. (D) Assertion (A) is incorrect, but Reason (R) is correct statement.

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

[1]

Q18.

Assertion (A) : Linkage isomerism arises in coordination compounds because of ambidentate ligand. Reason (R) : Ambidentate ligand like NO₂ has two different donor atoms i.e., N and O. (A) Both Assertion (A) and Reason (R) are correct statements, and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are correct statements, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is correct, but Reason (R) is incorrect statement. (D) Assertion (A) is incorrect, but Reason (R) is correct statement.

[1]

Q19.

Assertion (A) : Sucrose is a non-reducing sugar. Reason (R) : Sucrose has glycosidic linkage. (A) Both Assertion (A) and Reason (R) are correct statements, and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are correct statements, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is correct, but Reason (R) is incorrect statement. (D) Assertion (A) is incorrect, but Reason (R) is correct statement.

[1]

Q20.

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 correct statements, and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are correct statements, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is correct, but Reason (R) is incorrect statement. (D) Assertion (A) is incorrect, but Reason (R) is correct statement.

[1]

Section B

Short answer · 2 marks each · 7 of 7 shown

Q1.

Define the following terms: (a) Tranquilizers (b) Antiseptic OR Explain the cleansing action of soaps.

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

[2]

Q2.

For a 5% solution of urea (Molar mass = 60 g/mol), calculate the osmotic pressure at 300 K. [R = 0·0821 L atm K⁻¹ mol⁻¹] OR Visha took two aqueous solutions — one containing 7·5 g of urea (Molar mass = 60 g/mol) and the other containing 42·75 g of substance Z in 100 g of water, respectively. It was observed that both the solutions froze at the same temperature. Calculate the molar mass of Z.

[2]

Q3.

Analyse the given graph, drawn between concentration of reactant (y-axis) vs. time (x-axis). The curve starts at a concentration of about 1.7 and falls smoothly (a downward-curving line); the marked points show concentration ≈ 0.8 at time =10, ≈ 0.4 at time =20 and ≈ 0.2 at time =30 (the concentration is halved over each successive equal interval of time), approaching zero asymptotically. (a) Predict the order of reaction. (b) Theoretically, can the concentration of the reactant reduce to zero after infinite time? Explain.

[2]

Page 3 of 6

Q4.

Draw the shape of the following molecules: (a) XeOF₄ (b) BrF₃

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

[2]

Q5.

Give the formulae of the following compounds: (a) Potassium tetrahydroxidozincate (II) (b) Hexaammineplatinum (IV) chloride

[2]

Q6.

What happens when (a) Propanone is treated with methylmagnesium iodide and then hydrolysed, and (b) Benzene is treated with CH₃COCl in presence of anhydrous AlCl₃?

[2]

Q7.

Write the names and structures of monomers in the following polymers: (a) Bakelite (b) Neoprene

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

[2]

Section C

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

Q1.

Give the structures of A and B in the following sequence of reactions: (a) CH₃COOH xrightarrowNH₃ A xrightarrowNaOBr B (b) C₆H₅NO₂ xrightarrowHCl/Fe A xrightarrow[0-5°C]NaNO₂,HCl B (c) C₆H₅N₂Cl xrightarrowCuCN A xrightarrowH₂O/H^+ B OR (a) How will you distinguish between the following pairs of compounds: (i) Aniline and Ethanamine (ii) Aniline and N-methylaniline (b) Arrange the following compounds in decreasing order of their boiling points: Butanol, Butanamine, Butane

[3]

Q2.

Give the plausible explanation for the following: (a) Glucose doesn't give 2,4-DNP test. (b) The two strands in DNA are not identical but are complementary. (c) Starch and cellulose both contain glucose unit as monomer, yet they are structurally different.

[3]

Page 4 of 6

Q3.

Account for the following: (a) Sulphurous acid is a reducing agent. (b) Fluorine forms only one oxoacid. (c) Boiling point of noble gases increases from He to Rn. OR Complete the following chemical reactions: (a) MnO₂ + 4HCl arrow (b) XeF₆ + KF arrow (c) I^-(aq) + H^+(aq) + O₂(g) arrow

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

[3]

Q4.

Explain the role of the following: (a) NaCN in the separation of ZnS and PbS. (b) SiO₂ in the metallurgy of Cu containing Fe as impurity. (c) Iodine in the refining of Ti.

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

[3]

Q5.

Give three points of difference between physisorption and chemisorption.

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

[3]

Q6.

How will the rate of the reaction be affected when (a) Surface area of the reactant is reduced, (b) Catalyst is added in a reversible reaction, and (c) Temperature of the reaction is increased?

[3]

Q7.

Calculate the mass of ascorbic acid (Molar mass = 176 g mol⁻¹) to be dissolved in 75 g of acetic acid, to lower its freezing point by 1·5°C. (Kf = 3·9 K kg mol⁻¹)

[3]

Page 5 of 6

Section D

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

Q1.

(a) Calculate Δ G for the reaction Zn(s) + Cu²⁺(aq) arrow Zn²⁺(aq) + Cu(s). Given : E^° for Zn²⁺/Zn = -0·76 V and E^° for Cu²⁺/Cu = +0·34 V R = 8·314 JK⁻¹ mol⁻¹ F = 96500 C mol⁻¹. (b) Give two advantages of fuel cells. OR (a) Out of the following pairs, predict with reason which pair will allow greater conduction of electricity: (i) Silver wire at 30°C or silver wire at 60°C. (ii) 0·1 M CH₃COOH solution or 1 M CH₃COOH solution. (iii) KCl solution at 20°C or KCl solution at 50°C. (b) Give two points of differences between electrochemical and electrolytic cells.

[5]

Q2.

(a) Account for the following: (i) Copper (I) compounds are white whereas Copper (II) compounds are coloured. (ii) Chromates change their colour when kept in an acidic solution. (iii) Zn, Cd, Hg are considered as d-block elements but not as transition elements. (b) Calculate the spin-only moment of Co²⁺ (Z = 27) by writing the electronic configuration of Co and Co²⁺. OR (a) Give three points of difference between lanthanoids and actinoids. (b) Give reason and select one atom/ion which will exhibit asked property: (i) Sc³⁺ or Cr³⁺ (Exhibit diamagnetic behaviour) (ii) Cr or Cu (High melting and boiling point)

[5]

Q3.

(a) Out of t-butyl alcohol and n-butanol, which one will undergo acid catalyzed dehydration faster and why? (b) Carry out the following conversions: (i) Phenol to Salicylaldehyde (ii) t-butylchloride to t-butyl ethyl ether (iii) Propene to Propanol OR (a) Give the mechanism for the formation of ethanol from ethene. (b) Predict the reagent for carrying out the following conversions: (i) Phenol to benzoquinone (ii) Anisole to p-bromoanisole (iii) Phenol to 2,4,6-tribromophenol

[5]

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