Chemistry Sample Paper for Class 12 With Solution NCERT CBSE Board 2020

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Class 12 Subject Chemistry Paper Set 4 with Solutions

SECTION – A

Read the given passage and answer the questions 1 to 5 that follow :

Colloidal particles always carry an electric charge which may be either positive or negative. For example, when AgNO3 solution is added to KI solution, a negatively charged colloidal sol is obtained. The presence of equal and similar charges on colloidal particles provide stability to the colloidal sol and if, somehow, charge is removed, coagulation of sol occurs. Lyophobic sols are readily coagulated as compare to lyophilic sols.

Question 1: (Marks 1)

What is the reason for the charge on sol particles ?

Answer :

Due to preferential adsorption of common ions from solution / due to electron capture by sol particles during electrodispersion of metal/ due to formulation of electrical double layer

Question 2: (Marks 1)

Why the presence of equal and similar charges on colloidal particles provide stability ?

Answer :

Due to repulsion between the particles of similar charge.

Question 3: (Marks 1)

Why a negatively charged sol is obtained on adding AgNO₃ solution to KI solution ?

Answer :

Due to preferential adsorption of I^– from dispersion medium

Question 4: (Marks 1)

Name one method by which coagulation of lyophobic sol can be carried out.

Answer :

By electrophoresis / by mixing two oppositely charged sols / by boiling / by persistent dialysis / by addition of electrolyte.

Question 5: (Marks 1)

Out of KI or K₂SO₄ , which electrolyte is better in the coagulation of positive sol ?

Answer :

K₂SO₄

Questions 6 to 10 are one word answers :

Question 6: (Marks 1)

Name the method applied for the concentration of Bauxite ore in the extraction of Aluminium.

Answer :

Leaching / Baeyer’s process

Question 7: (Marks 1)

Answer :

Question 8: (Marks 1)

Write an isomer of C₃H₉N which gives foul smell of isocyanide when treated with chloroform and ethanolic NaOH.

Answer :

CH₃–CH₂–CH₂–NH₂

Question 9: (Marks 1)

Which one of the following is an antidepressant drug ? Chloramphenicol, Luminal, Bithional

Answer :

Luminal

Question 10: (Marks 1)

Write the name of component of starch which is water soluble.

Answer :

Amylose

Questions 11 to 15 are Multiple Choice Questions :

Question 11: (Marks 1)

How many ions are produced from the complex [Co(NH3 )5Cl] Cl2 in solution ?

(a) 4

(b) 2

(d) 5

Answer :

Question 12: (Marks 1)

In a lead storage battery

(a) PbO2 is reduced to PbSO4 at the cathode.

(b) Pb is oxidised to PbSO4 at the anode.

(d) All the above are true.

Answer :

(d) All the above are true.

Question 13: (Marks 1)

The slope in the plot of ln [R] Vs. time gives

Answer :

Question 14: (Marks 1)

The pair [Co(NH₃)₄Cl₂] Br₂ and [Co(NH₃)₄ Br₂] Cl₂ will show

(a) Linkage isomerism

(b) Hydrate isomerism

(d) Coordinate isomerism

Answer :

Question 15: (Marks 1)

An α-helix is a structural feature of

(a) Sucrose

(b) Polypeptides

(d) Starch

Answer :

Questions 16 to 20 :

(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).

(D) Assertion (A) is wrong, but Reason (R) is correct statement.

Question 16: (Marks 1)

Assertion (A) : F2 is a strong oxidising agent.

Reason (R) : Electron gain enthalpy of fluorine is less negative.

Answer :

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

Question 17: (Marks 1)

Assertion (A) : (CH₃)₃ C–O–CH₃ gives (CH₃)₃ C–I and CH₃OH on treatment with HI.

Reason (R) : The reaction occurs by SN1 mechanism.

Answer :

(A) Both Assertion (A) and Reason (R) are correct statements, and Reason (R) is the correct explanation of the Assertion (A).

Question 18: (Marks 1)

Assertion (A) : Transition metals have low melting points.

Reason (R) : The involvement of greater number of (n – 1)d and ns electrons in the interatomic metallic bonding.

Answer :

(D) Assertion (A) is wrong, but Reason (R) is correct statement.

Question 19: (Marks 1)

Assertion (A) : Hydrolysis of an ester follows first order kinetics.

Reason (R) : Concentration of water remains nearly constant during the course of the reaction.

Answer :

(A) Both Assertion (A) and Reason (R) are correct statements, and Reason (R) is the correct explanation of the Assertion (A).

Question 20: (Marks 1)

Assertion (A) : Benzoic acid does not undergo Friedal-Crafts reaction.

Reason (R) : The carboxyl group is activating and undergo electrophilic substitution reaction.

Answer :

SECTION – B

Question 21: (Marks 2)

What happens when

(i) a pressure greater than osmotic pressure is applied on the solution side separated from solvent by a semipermeable membrane ?

(ii) acetone is added to pure ethanol ?

Answer :

(i) Reverse osmosis occurs.

(ii) Solution shows positive deviation from Raoult’s Law.

Question 22: (Marks 2)

Write the principle of the following refining methods :

(a) vapour phase refining

(b) chromatography

Write chemical equations involved to obtain :

(i) Cu from Cu₂S

(ii) Ag from [Ag (CN)₂]^– complex

Answer :

Write the principle of the following refining methods

Question 23: (Marks 2)

Write the balanced chemical equations involved in the preparation of KMnO₄ from pyrolusite ore (MnO₂).

Write the balanced ionic equations showing the oxidising action of acidified dichromate (Cr₂O^2–₇) solution with (i) Iron (II) Ion and (ii) tin (II) ion.

Answer :

Write the balanced chemical equations involved in the preparation of

Question 24: (Marks 2)

Write the IUPAC names and hybridisation of the following complexes :

(i) [Ni(CN)₄]^2–

(ii) [Fe(H₂O)₆]²⁺

(Given : Atomic number Ni = 28, Fe = 26)

Answer :

(i) Tetracyanidonickelate(II) / Tetracyanonickelate(II)

dsp²

(ii) Hexaaquairon(II)

sp³d²

Question 25: (Marks 2)

Define the following terms with a suitable example in each :

(i) Antibiotics

(ii) Antiseptics

Answer :

(i) A chemical substance which in low concentrations inhibits the growth or destroys microorganisms.

eg: Pencillin / Ofloxacin / Chloramphenicol / Tetracycline

(ii) Antiseptics are the chemical substances applied to the living tissues which prevent the growth or kill the microorganisms.

eg: Dettol / Furacine / Soframycine.

(or any other suitable example)

Question 26: (Marks 2)

Write the reactions showing the presence of following in the open structure of glucose :

(i) a carbonyl group

(ii) Straight chain with six carbon atoms

Answer :

Write the reactions showing the presence of following in the open

Question 27: (Marks 2)

State Henry’s law. Calculate the solubility of CO₂ in water at 298 K under 760 mm Hg.

(K_H for CO₂ in water at 298 K is 1.25 × 10⁶ mm Hg)

Answer :

State Henry’s law. Calculate the solubility of CO2

SECTION – C

Question 28: (Marks 3)

The freezing point of a solution containing 5g of benzoic acid (M = 122 g mol^–1) in 35g of benzene is depressed by 2.94 K. What is the percentage association of benzoic acid if it forms a dimer in solution ? (K_f for benzene = 4.9 K kg mol^–1)

Answer :

The freezing point of a solution containing 5g of benzoic acid (M = 122 g

Question 29: (Marks 3)

The rate constant for the first order decomposition of N₂O₅ is given by the following equation : k = (2.5 × 10¹⁴ s^–1) e^{(–25000K)/T} Calculate Ea for this reaction and rate constant if its half-life period be 300 minutes.

Answer :

The rate constant for the first order decomposition of N2O5