The sample paper is one of the best resources for the student to prepare for the
exam. These help the student to get a prior experience before they attempt for
the final exam also, they will know if they are prepared for the exam
completely or not. They can test their knowledge for all these subjects and get
confident about the answer. if any discrepancies occur in the written answer,
they can focus more on such a question, so that there are no mistakes happening
in the final paper. they can also mark themselves for correct and wrong
answers.
Structure
of CBSE Class 12th Chemistry Model Paper 2020
Chemistry the paper will be of three hours and a total of 70 marks. the paper will consist of 37 questions in all divided
into three sections.
Section
A: Objective type question.
There
will be a very short type question 1 to
20 in this section. each question will
have 1 mark.
Section
B: Short answer questions.
There
will be Short answer questions of 21 to 27, each question will have 2 marks.
Section
C: Long answer questions
There
will be long answer questions of 28 to 34, each question will have 3 marks.
Section
D: Long answer question
There
will be also again long answer question of 35 to 37, each The question will
have 5 marks each.
There
is no overall choice. However, an internal choice has been provided in two
questions of two marks, two questions of three marks and all the three questions
of five marks. You have to attempt only one of the choices in such
questions.
SECTION - A
Read
the given passage and answer the questions 1 to 5that follow:
A Lead the storage battery is the most important type of secondary cell having a lead
anode and a grid of lead packed with PbO2 as a cathode. A 38% solution of sulphuric
acid is used as an electrolyte. (Density=1.294 g mL-1) The battery holds 3.5 L of
the acid. During the discharge of the battery, the density of H2SO4 falls to
1.139 g mL-1. (20% H2SO4 by mass)
(1) Write the reaction taking place at
the cathode when the battery is in use.
(2) How much electricity in terms of
Faraday is required to carry out the reduction
of one mole of PbO2?
(3) What is the molarity of sulphuric
acid before discharge?
(4) The lead storage battery is considered
a secondary cell. Why?
(5) Write the products of electrolysis
when dilute sulphuric acid is electrolyzed using
Platinum electrodes.
Questions
6 to 10 are one-word answers:
(6) Name the substance used as a depressant
in the separation of two sulfide ores
in the Froth floatation method.
(7) Name the unit formed by the
attachment of a base to 1 position of sugar in a nucleoside.
(8) Name the species formed when an aqueous solution of amino acid is dissolved
in water?
(9) What type of reaction occurs in
the formation of Nylon 6,6 polymer?
(10) Which of the following compounds
would undergo Cannizzaro reaction:
Benzaldehyde, Cyclohexanone,
2- Methylpentanal.
Questions
11 to 15 are multiple choice questions:
(11) The IUPAC name of the compound
shown below is:
(a) 2-bromo-6-chlorocyclohex-1-ene
(b) 6-bromo-2-chlorocyclohexene
(c) 3-bromo-1-chlorocyclohexene
(d) 1-bromo-3-chlorocyclohexene
(12) When one mole of CoCl3.5NH3 was treated with
excess of silver nitrate solution, 2 mol of AgCl was precipitated. The formula
of the compound is:
(a) [Co(NH3)5Cl2]Cl
(b) [Co(NH3)5Cl]Cl2
(c) [Co(NH3)4Cl2] (NH3)Cl
(d) [Co(NH3) Cl3] (NH3)2
(13) The
absorption maxima of several octahedral complexions are as follows:
S.No
|
Compound
|
lmax nm
|
1
|
[Co(NH3)6]3+
|
475
|
2
|
[Co(CN)6]3-
|
310
|
3
|
[Co(H2O)6]3+
|
490
|
The crystal field splitting
is maximum for :
(a) [Co(H2O)6]3+
(b) [Co(CN)6]3-
(c) [Co(NH3)6]3+
(d) All the complexions have the same splitting, Δo ,
(14) Predict
the number of ions produced per formula unit in an aqueous solution of
[Co(en)3]Cl3
(a) 4
(b) 3
(c) 6
(d) 2
(15)
The incorrect statement about LDP is:
(a) It is obtained through the free radical addition of ethene.
(b) It consists of linear molecules.
(c) It is obtained by the
H-atom abstraction. (d) Peroxide is used as an initiator.
Questions
16 to 20 :
(A)Both
assertion and reason are correct statements, and the reason is the correct
explanation of the assertion.
(B)Both
assertion and reason are correct statements, but the reason is not the correct
explanation of the assertion.
(C)Assertion
is correct, but the reason is the wrong statement.
(D)Assertion
is wrong, but the reason is the correct statement.
16. Assertion: The two strands in
double-strand helix structure of DNA are complementary to each other
Reason: Disulphide bonds are formed between specific pairs of bases
17. Assertion: Glucose reacts with
hydroxylamine to form an oxime and also adds a molecule of hydrogen cyanide to
give cyanohydrin.
Reason: The carbonyl group is
present in the open-chain structure of glucose.
18. Assertion: The acidic strength of
halogen acids varies in the order HF>HCl>HBr>HI
Reason: The bond dissociation enthalpy
of halogen acids decreases in the order HF>HCl>HBr>HI
19. Assertion: C2H5OH
is a weaker base than phenol but is a stronger nucleophile than phenol. (1)
Reason: In phenol the lone
pair of electrons on oxygen is withdrawn towards the ring due to resonance.
20. Assertion:
Aryl halides undergo nucleophilic substitution reactions with ease.
Reason: The carbon halogen
bond in aryl halides has partial double bonds character.
SECTION: B
21. Calculate
the number of lone pairs on the central atom in the following molecule and predict
the geometry.
XeF4
22. The rate of a reaction depends
upon the temperature and is quantitatively expressed as
k=Ae-Ea/RT
i) If
a graph is plotted between log k and 1/T, write the expression for the slope
of the reaction?
ii) If
at under different conditions Ea1 and Ea2 are the activation energy of two reactions If Ea1 = 40 J / mol and Ea2
= 80 J / mol. Which of the two has a larger
value of the rate constant?
23.
The experimentally determined molar mass for what type of substances is always
lower than the true value when water is used as a solvent. Explain. Give one
example of such a substance and one example of a substance which does not show
a large variation from the true value.
24. Write
structure of the products formed:
25.
Draw one of the geometrical isomers of the complex [Pt (en)2 Cl2 ]2+ which is optically
inactive.
Also, write the name of this entity according to the IUPAC nomenclature.
OR
Discuss
the bonding in the coordination entity [CO(NH3)6 ]3+
on the basis of valence bond theory. Also, comment on the geometry and spin of
the given entity. (Atomic no. of Co= 27)
26. What is meant by the Vapour phase refining?
Write any one example of the process which illustrates this technique, giving
the chemical equations involved.
OR
Write and explain the reactions
involved in the extraction of gold.
27. Which one of the following
compounds will undergo hydrolysis at a faster rate by the SN1 mechanism? Justify.
SECTION: C
28. Calculate
the freezing point of a solution containing 0.5 g KCl (Molar mass = 74.5 g/mol)
dissolved in 100 g water, assuming KCl to be 92% ionized.
Kfof water = 1.86
K kg / mol.
29. For
the reaction A + B →products, the following initial rates were obtained at
various given initial concentrations
S.No.
|
[A] mol / L
|
[B] mol / L
|
Initial rate M/s
|
1.
|
0.1
|
0.1
|
0.05
|
2.
|
0.2
|
0.1
|
0.10
|
3.
|
0.1
|
0.2
|
0.05
|
Determine
the half-life period.
OR
The first-order reaction is 50 % complete in 50 minutes at 300 K and the same the reaction is again 50 % complete in 25 minutes at 350 K. Calculate activation the energy of the reaction.
30. Answer
the following questions:
(a) Which of the following
electrolytes are most effective for the coagulation of AgI/Ag+ sol?
a. MgCl2, K2SO4,
K4[Fe(CN)6]
(b)What happens when a
freshly precipitated Fe(OH)3 is shaken with a little
amount of dilute solution of FeCl3.
(c) Out of sulphur sol and
proteins, which one forms macromolecular colloids?
31. Account
for the following:
a) Moist SO2 decolorizes the KMnO4 solution.
b) In general interhalogen compounds are more reactive than halogens (except fluorine).
c) Ozone acts as a powerful oxidizing agent
32. Identify
the product formed when propane-1-ol is treated with Conc. H2SO4 at
413 K. Write the mechanism involved in the above reaction.
33. (a) Give chemical tests to distinguish between
the following pairs of compounds:
(i) Ethanal and
Propanone.
(ii) Pentan-2-one
and Pentan-3-one.
(b) Arrange the following compounds in increasing order of their
acid strength: Benzoic acid, 4- Nitrobenzoic acid, 3,4-Dinitrobenzoic acid,
4- Methoxybenzoic
acid.
OR
Compare
the reactivity of benzaldehyde and ethanal towards nucleophilic addition
reactions. Write the cross aldol condensation product between benzaldehyde and
ethanal.
34. Define
and write an example for the following
(a) Broad
spectrum antibiotics.
(b) Analgesics
SECTION: D
35. (a) The e.m.f. of the following a cell at 298 K is 0.1745 V
Fe (s) / Fe 2+
(0.1 M) // H+ (x M)/ H2 (g) (1 bar)/ Pt (s)
Given : E0Fe2+
/Fe = - 0.44V
Calculate
the H+ ions concentration of the solution at the electrode where hydrogen is
being produced.
(b) An aqueous solution of copper sulfate and silver nitrate are
electrolyzed by 1 ampere current for 10 minutes in separate electrolytic cells.
Will the mass of copper and silver deposited on the cathode be the same or different?
Explain your answer.
OR
(a)
Calculate the degree of dissociation of 0.0024 M acetic acid if the conductivity of
this solution is 8.0 × 10-5 S cm-1.
Given l0H+ =349.6Scm2 mol-1;
lOch3COO- =40.9S cm2 mol-1
(b)
Solutions of two electrolytes ‘A’ and ‘B’ are diluted. The limiting molar
conductivity of ‘B’ increases to a smaller extent while that of ‘A’ increases
to a much larger extent comparatively. Which of the two is a strong
electrolyte? Justify your answer.
36. An
organic compound A’ with molecular formula C7H7NO reacts
with Br2/aqKOH to give compound B’, which upon reaction with NaNO2&
HCl at O°C gives C’. Compound C’ on heating with CH3CH2OH
gives a hydrocarbon D’. Compound B’ on further reaction with Br2 water gives
white precipitate of compound E’. Identify the compound A, B, C, D&E; also
justify your answer by giving relevant chemical equations.
OR
(a) How will you convert:
(i) Aniline
into Fluorobenzene.
(ii) Benzamide
into Benzylamine.
(iii) Ethanamine
to N, N-Diethylethanamine.
(b)
Write the structures of A and B in the following:
37. (a) When a chromite ore (A) is fused with an
aqueous solution of sodium carbonate in free excess of air, a yellow solution
of compound (B) is obtained. This solution is filtered and acidified with
sulphuric acid to form a compound (C). Compound (C) on treatment with the solution of
KCl gives orange crystals of compound (D). Write the chemical formulae of
compounds A to D.
(b) Describe the cause of the following variations with respect to
lanthanoids and actinoids:
(i) Greater range of
oxidation states of actinoids as compared to lanthanoids.
(ii) Greater actinoid
contraction as compared to lanthanoid contraction.
(iii) Lower ionization
enthalpy of early actinoids as compared to the early lanthanoids.
OR
(a)
What happens when
(i) Manganate ions (MnO2 - ) undergoes
disproportionation reaction in acidic medium?
(ii) Lanthanum is heated with Sulphur?
(b)
Explain the following trends in the properties of the members of the First
series of transition elements:
(i)Eo(M2+
/M)value for copper is positive(+0.34 V) in contrast to the
other
members of the series.
(ii) Cr2+
is reducing while Mn3+ is oxidising, though both have d4 configuration.
(iii) The oxidising power in the series increases in the
order. VO+2< Cr2O2-7 <MnO-4
