CBSE Class 12 Previous Year Question Papers With Solutions pdf Chemistry

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Class 12 Subject Chemistry Paper Set 2 with Solutions

SECTION A

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

Organic compounds containing amine as functional group are present in a vivid variety of compounds, namely amino acids, hormones, neurotransmitters, DNA, alkaloids, dyes, etc. Drugs including nicotine, morphine, codeine and heroin, etc. which have physiological effects on humans also contain amino group in one form or another. Amines are basic because of the presence of lone pair of electrons on nitrogen. Addition of nitrogen into an organic framework leads to the formation of two families of molecules, namely amines and amides. As chemistry students, we must appreciate the versatility of nitrogen.

Question 1: (Marks 1)

What are amino acids ?

Answer :

Simple organic compounds containing both carboxyl (—COOH) and amino (—NH₂) group. /

Building blocks of protein. /

Amino substituted carboxylic acid / structure

Question 2: (Marks 1)

Why are amino acids amphoteric ?

Answer :

They contain both acid (-COOH) and basic(NH2) group /

Zwitter ion form or structure /

It can react both acids and bases.

Question 3: (Marks 1)

Give one point of difference between acidic and basic amino acid.

Answer :

Acidic aminoacids- will have more number of carboxyl groups than amino groups. /

Basic amino acids- will have more number of amino groups than carboxyl groups.

Question 4: (Marks 1)

What are essential amino acids ?

Answer :

Those which are not synthesized in our body or must be supplied through diet.

Question 5: (Marks 1)

Name the linkage formed when carboxyl end of one amino acid condenses with amino end of other amino acid.

Answer :

Questions number 6 to 10 are one word answers :

Question 6: (Marks 1)

Name the process used for the benefaction of ores if the ore is soluble in some suitable solvent.

Answer :

Leaching

Question 7: (Marks 1)

Give an example of a metal which can be purified by the process of distillation.

Answer :

Zinc, Mercury or any other suitable metal

Question 8: (Marks 1)

What type of isomerism is shown by the complex [Co(NH₃)₅ NO₂ ] Cl₂ ?

Answer :

Linkage

Question 9: (Marks 1)

An organic compound is adsorbed on the surface of silica gel. Name the process of removing the organic compound from silica gel.

Answer :

Desorption

Question 10: (Marks 1)

Calculate the overall order of the reaction whose rate law expression was predicted as : Rate = k[NO]^3/2[O₂]^1/2.

Answer :

Questions number 11 to 15 are multiple choice questions :

Question 11: (Marks 1)

50 mL of an aqueous solution of glucose C6H12O6 (Molar mass : 180 g/mol) contains 6·02  1022 molecules. The concentration of the solution will be

(A) 0·1 M

(B) 0·2 M

(D) 2·middot;0 M

Answer :

(D) 2·0 M

Question 12: (Marks 1)

If the standard electrode potential of an electrode is greater than zero, then we can infer that its

(A) reduced form is more stable compared to hydrogen gas.

(B) oxidised form is more stable compared to hydrogen gas.

(D) reduced form is less stable than the hydrogen gas.

Answer :

(A) reduced form is more stable compared to hydrogen gas.

Question 13: (Marks 1)

Total number of unpaired electrons present in Co3+ (Atomic number = 27) is

(A) 2

(B) 7

(D) 5

Answer :

1 Mark will be given if attempted / if written none of the answer is right / 4

Question 14: (Marks 1)

The incorrect statement about interstitial compounds is

(A) They are chemically reactive.

(B) They are very hard.

(D) They have high melting point.

Answer :

(A) They are chemically reactive.

Question 15: (Marks 1)

The correct IUPAC name

Answer :

For questions number 16 to 20, two statements are given - one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (i), (ii), (iii) and (iv) as given below :

(i) Both assertion (A) and reason (R) are correct statements, and reason (R) is the correct explanation of the assertion (A).

(ii) Both assertion (A) and reason (R) are correct statements, but reason (R) is not the correct explanation of the assertion (A).

(iii) Assertion (A) is correct, but reason (R) is incorrect statement.

(iv) Assertion (A) is incorrect, but reason (R) is correct statement.

Question 16: (Marks 1)

Assertion (A) : Boiling points of alkyl halides decrease in the order R-I > R-Br > R-Cl > R-F.

Reason (R) : Van der Waals forces decrease with increase in the size of halogen atom.

Answer :

(iii) Assertion (A) is correct, but reason (R) is incorrect statement.

Question 17: (Marks 1)

Assertion (A) : Low spin tetrahedral complexes are rarely observed.

Reason (R) : The orbital splitting energies are not sufficiently large to forcing pairing.

Answer :

(i) 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) : Albumin is a globular protein.

Reason (R) : Polypeptide chain coils around to give a straight chain.

Answer :

(iii) Assertion (A) is correct, but reason (R) is incorrect statement.

Question 19: (Marks 1)

Assertion (A) : Bakelite is a thermosetting polymer.

Reason (R) : On heating, polymeric chain becomes a long and straight chain.

Answer :

(iii) Assertion (A) is correct, but reason (R) is incorrect statement.

Question 20: (Marks 1)

Assertion (A) : o-nitrophenol is a weaker acid than p-nitrophenol.

Reason (R) : Intramolecular hydrogen bonding makes ortho isomer weaker than para isomer.

Answer :

(i) Both assertion (A) and reason (R) are correct statements, and reason (R) is the correct explanation of the assertion (A).

SECTION B

Question 21: (Marks 2)

Give one point of difference between the following :

(a) Tranquilizers and Analgesics

(b) Antiseptics and Disinfectants

Differentiate on the basis of chemical composition between cationic and anionic detergents. Also give one example of each category.

Answer :

Give one point of difference between the following

Question 22: (Marks 2)

Give reasons for the following

Answer :

(a) Due to lone pair -lone pair repulsion on oxygen.

(b) Due to resonance in phenol and not in methanol / sp² hybridised carbon atom in phenol / sp³ hybridised carbon atom in methanol.

Question 23: (Marks 2)

Complete and balance the following chemical equations :

(a) MnO^-₄ + H₂O + I^-

(b) MnO^-₄ + H⁺ + I^-

Answer :

Complete and balance the following chemical equations

Question 24: (Marks 2)

Define adsorption isotherm. Give the empirical relationship between the quantity of gas adsorbed by unit mass of solid absorbent and pressure at a particular temperature.

Define shape-selective catalysis. Name the process by which alcohols convert directly into gasoline and give a variety of hydrocarbons.

Answer :

The curve obtained by plotting the amount of gas adsorbed by the adsorbent with pressure at constant temperature.

x/m = kp^1/n

The catalytic reaction that depends upon the pore structure of the catalyst and the size of the reactant and product molecules.

Shape selective catalysis / Catalytic dehydration .

Question 25: (Marks 2)

A reaction is first order w.r.t. reactant A as well as w.r.t. reactant B. Give the rate law. Also give one point of difference between average rate and instantaneous rate.

Answer :

Rate = k[A][B]

Average rate - Rate of a reaction for a particular period or interval of time. Instantaneous rate - Rate of a reaction at a particular instant of time.

(or any other suitable difference)

Question 26: (Marks 2)

For an electrochemical cell

Mg (s) + Ag⁺ (aq) → Ag (s) + Mg²⁺ (aq),

give the cell representation. Also write the Nernst equation for the above cell at 25°C.

Answer :

For an electrochemical cell

Question 27: (Marks 2)

Predict the state of the solute in the solution in the following situations :

(a) When ‘i’ is found to be more than one.

(b) When ‘i’ is found to be less than one.

Answer :

(a) Dissociated

(b) Associated

SECTION C

Question 28: (Marks 3)

Give the structures of the monomers of the following polymers :

(a) Teflon

(b) Glyptal

Write the names of monomers of the following polymers :

Write the names of monomers of the following polymers

Answer :

Give the structures of the monomers of the following polymers

Question 29: (Marks 3)

Account for the following :

(a) Aniline is a weaker base compared to ethanamine.

(b) Aniline does not undergo Friedel-Crafts reaction.

Answer :

(a) the lone pair of nitrogen in aniline is in resonance or conjugation with the benzene ring.

(b) Aniline forms salt with anhydrous AlCl3 .

Question 30: (Marks 3)

Justify and arrange the following compounds of each set in increasing order of reactivity towards the asked displacement :

(a) 1-Bromobutane, 2-Bromobutane, 2-Bromo-2-Methylpropane (S_N1 reaction)

(b) 1-Bromobutane, 2-Bromobutane, 2-Bromo-2-Methylpropane (S_N2 reaction)

Answer :

(a) 1-bromobutane< 2-bromobutane< 2-bromo-2-methylpropane.

Tertiary carbo cation is more stable than secondary than primary.

(b) 2-bromo-2-methyl propane < 2-bromobutane< 1-bromobutane.

due to decrease in steric hindrance.

Question 31: (Marks 3)

(a) Give the IUPAC name and electronic configuration of central metal atom in terms of t_2g and e_g of K₄ [Mn(CN)₆].

(b) What is meant by ‘Chelate effect’ ? Give an example.

Write the hybridisation and magnetic characters of the following complexes :

(i) [Fe(CN)₆]^4–

(ii) [CoF₆]^3–

(iii) [Ni(CO)₄]

[Atomic number : Fe = 26, Co = 27, Ni = 28]

Answer :

Give the IUPAC name and electronic configuration of central metal

Question 32: (Marks 3)

Give the chemical reactions involved in the leaching of alumina from bauxite.

Answer :

Give the chemical reactions involved in the leaching of alumina from

Question 33: (Marks 3)

Conductivity of 2 x 10^–3 M methanoic acid is 8 x 10^–5 S cm^–1 . Calculate its molar conductivity and degree of dissociation if for methanoic acid is 404 S cm2 mol^–1.

Answer :

Conductivity of 2 ? 10–3 M methanoic acid is 8 ? 10–5 S cm–1

Question 34: (Marks 3)

An antifreeze solution is prepared by dissolving 31 g of ethylene glycol (Molar mass = 62 g mol^–1 ) in 600 g of water. Calculate the freezing point of the solution. (Kf for water = 1·86 K kg mol^–1)

Answer :

An antifreeze solution is prepared by dissolving 31 g of ethylene glycol

SECTION D

Question 35: (Marks 5)

Visha plotted a graph between concentration of R and time for a

Answer :

Visha plotted a graph between concentration of R and time for a

Question 36: (Marks 5)

An amorphous solid ‘A’ which has a crown shaped structure, burns in air

Answer :

An amorphous solid ‘A’ which has a crown shaped structure, burns in air

(ii) 2I^-_(aq.)+ H₂O_(l) +O_3(g) → I_2(s) + O_2(g) + 2OH^-_(aq.)

Question 37: (Marks 5)

(a) An organic compound ‘A’ having molecular formula C₅H₁₀O gives negative Tollens’ test, forms n-pentane on Clemmensen reduction but doesn’t give iodoform test. Identify ‘A’ and give all the reactions involved.

(b) Carry out the following conversions :

(i) Propanoic acid to 2-Bromopropanoic acid

(ii) Benzoyl chloride to benzaldehyde

Complete the following sequence of reactions