CBSE Sample Paper 2021 Class 12 Chemistry New Pattern

CBSE Sample Paper 2021 Class 12 Chemistry New Pattern

CLASS-12

SUBJECT-CHEMISTRY

T.T. -3 Hr

M.M.-70

General Instructions

  • This question paper comprises four Sections – A, B,C and D. There are 37 questions in the question paper. All questions are compulsory.
  • Section A – Questions no. 1 to 20 are very short answer type questions carrying 1 mark each. Answer these questions in one word or one sentence.
  • Section B – Questions no. 21 to 27 are short answer type questions, carrying 2 marks each.
  • Section C –Questions no. 28 to 34 are long answer type-I questions, carrying 3 marks each.
  • Section D –Questions no. 35 to 37 are long answer type-II questions, carrying 5 marks each.
  • There is no overall choice in the question paper.

SECTION A

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. (1 x 5=5)

1) Why are Zn, Cd and Hg non-transition elements?

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

3) Why do transition metals and their compounds show catalytic activity?

4) Why are melting points of transition metals high?

5) Why is Cu 2+ ion coloured while Zn 2+ ion is colourless in aqueous solution?

Questions number 6 to 10 are one word answer:(1 x 5=5)

6) Write the IUPAC name and formula of given sequence-

i) [Cr(NH3)2Cl2 (en)]Cl

ii)Pentaaminenitrito-o-Cobalt(III)

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

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

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

10)What is the formula of a compound in which the element Y forms ccp lattice and atoms of X occupy 1/3rd of tetrahedral voids ?

Questions number 11 to 15 are multiple choice questions:(1 x 5=5)

11) Which of the following is most stable in aqueous solution?
a) Mn 2+

b) Cr 3+

c) V 3+

d) Ti 3+

12) Racemisation occurs in

a) SN2 reaction

b) SN1 reaction

c) Neither SN2 nor SN1 reactions

d) SN2 reaction as well SN1 reaction

13) C6H5CH2NH2on heating with CHCl3 and alcoholic KOH gives foul smell of

a) C6H5CH2OH

b)C6H5CH2NC

c)C6H5CH2CN

d)C6H5CH2Cl

14) 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

15) Peptide linkage is present in

a) Carbohydrates

b) Vitamins

c) Proteins

d) Rubber

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:(1 x 5 = 5)

(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.

16) Assertion (A): Conductivity of an electrolyte decreases with decrease in concentration.

Reason (R): Number of ions per unit volume increases on dilution.

17) 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.

18) 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.

19) Assertion (A): Osmotic pressure is a colligative property.

Reason (R): Osmotic pressure is directly proportional to molarity.

20) Assertion (A): Reactivity of ketones is more than aldehydes.

Reason (R): The carbonyl carbon of ketones is less electrophilic as compared to aldehydes.

Section – B

21) In the given reaction 2 A + 3 B → 2 C

The rate of formation of C is 2.5 ´ 10―4 mol L1s1,Calculate the

i) rate of reaction, and

ii) rate of disappearance of B.

22) Define the following terms with a suitable example of each:(2)

i) Associated colloids

ii) O/W emulsion

23) Write two differences between physisorption and chemisorption.

24) (a) Write the IUPAC name and hybridization of the complex [CoF6]3-.  (2)

(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.

25) Define dispersed phase and the dispersion medium. Discuss classification of colloids with example.

26) Define the following terms: (2)

i) Oligosaccharides

ii) Invert sugar

27) Write the products of the following reaction:

6 XeF4 + 12H2O →

Is this reaction a disproportionation reaction? Give reasons in support of your answer.(2)

SECTION C

28) Calculate the maximum work and log Kc for the given reaction at 298 K: (3)

Ni(s)+2Ag(aq)  → Ni2+(aq)+2Ag(s)

Given: E0Ni2+/Ni=-0.25V,E0Ag+/Ag=+0.80V       1F=96500C mol-1

29) 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? (3)

[Given : log 2 = 0.3010, log 3 = 0.4771, log 4 = 0.6021, log 5 = 0.6771, log 6 = 0.7782]

30) Define first order reaction. Calculate the half-life of a first order reaction from their rate constants given below:

a) 200 s-1

b) 2 min-1

c) 4 year-1

31) How can you convert the following:

i) Sodium phenoxide to o-hydroxybenzoic acid

ii) Acetone to propene

iii) Phenol to chlorobenzene

32) (a) Write the mechanism of the following reaction:(2+1=3)

2CH3CH2OH                        H+ 413K                        CH3CH2OCH2CH3 + H20

(b) Write the preparation of phenol from cumene.

33) Write the products formed when (CH3)3 C – CHO reacts with the following reagents:(3)

i) CH3COCH3 in the presence of dilute NaOH

ii) HCN

iii) Conc. NaOH

34) Define Lyophobic and Lyophilic sol with a suitable example of each. Why is coagulation of Lyophilic sol difficult as compared to Lyophobic sol?(3)

SECTION D

35) (a) Give reasons:(3)

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- (2)

i) an oxidizing agent, and

ii) a dehydrating agent.

OR (a) Account for the following:

i) Hydration enthalpy of Fion is more than Cl ion. (1)

ii) SO2 is a reducing agent, whereas TeO2 is an oxidizing agent in group- 16 oxides.(1)

(b) Write the reaction of F2 with water. Why does I2 not react with water? (1+1 = 2)

(c) Draw the structure of XeF2.(1)

36) (a) Give reasons :(3)

i) Although – NH2 group is o/p directing in electrophilic substitution reactions, yet aniline, on nitration gives good yield of m-nitroaniline.

ii) (CH3)2 NH is more basic than (CH3)3 N in an aqueous solution.

iii) Ammonolysis of alkyl halides is not a good method to prepare pure primary amines.

(b) Distinguish between the following:(2)

i) CH3CH2NH2 and (CH3CH2) 2 NH

ii) Aniline and CH3NH2

OR (a) Write the structures of A and B in the following reactions:(1 + 1 = 2)

i)C6H5N2+Cl           CuCN             A                     H2O/H+                      B

ii)CH3COOH                        NH3                 A                     NaOBr                       B

(b) Write the chemical reaction of methylamine with benzoyl chloride and write the IUPAC name of the product obtained. (1 + 1 = 2)

(c) Arrange the following in the increasing order of their pKb values :(1)

C6H5NH2, NH3, C2H5NH2, (C2H5) 2 NH

37) (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.(3)

(Given : R = 0.082 L atm K-1 mol-1)

(b) State Henry’s law. Why is air diluted with helium in the tanks used by scuba divers?(1 + 1 = 2)

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.(3)

[Given : Kf for water = 1.86 K kg mol-1]

(b) Give reasons :(1 + 1 = 2)

i) 0.1 M KCl has higher boiling point than 0.1 M Glucose.

ii) Meat is preserved for a longer time by salting.

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