MBOSE Class 12 Question Paper 2024 for Chemistry

Meghalaya Board of School Education

QUESTION
PAPERS

Total No. of Printed Pages—12
HS/XII/Sc/Ch/24

2024

CHEMISTRY

( Theory )

Full Marks : 70

Time : 3 hours

The figures in the margin indicate full marks for the questions

General Instructions :

(i) Attempt all parts of a question together in one place.

(ii) All questions are compulsory.

(iii) Section—A : Question Nos. 1 to 5 are of multiple choice
type, each carrying 1 mark.

(iv) Section—B : Question Nos. 6 to 12 are of short answer-
type questions and carry 2 marks each.

(v) Section—C : Question Nos. 13 to 24 are also short
answer-type questions and carry 3 marks each.

(vi) Section—D : Question Nos. 25 to 27 are long answer-type
questions and carry 5 marks each.

/30 [ P.T.O.

( 2 )

(vii) There is no overall choice. However, an internal choice
has been provided in four questions of 2 marks, four
questions of 3 marks, and all three questions of 5 marks
weightage. Students have to attempt only one of the
choices in such questions.
(viii) Use of non-programmable ordinary scientific calculators
and log tables are allowed.
(ix) Mobile phones and pagers are not allowed inside the
Examination Hall.

SECTION—A
( Marks : 5 )

Choose and write the correct answers for the following in
the answer script :

1. When benzoic acid is dissolved in benzene, the van’t Hoff
factor will be
(a) 1
(b) 0·5
(c) 2
(d) 1·5 1

2. A device that converts energy of combustion of fuels like
hydrogen and methane directly into electrical energy is
known as
(a) fuel cell
(b) electrolytic cell
(c) dynamo
(d) Nickel-Cadmium cell 1

HS/XII/Sc/Ch/24/30 [ Contd.

( 3 )

3. The number of d-electrons in [Cr(H2O)6 ] 3+ ion (atomic
number of Cr = 24) is

(a) 2

(b) 3

(c) 4

(d) 5 1

4. The existence of two different coloured complexes with
composition of [Co(NH 3 )4 Cl2 ] + is due to

(a) linkage isomerism

(b) geometrical isomerism

(c) coordination isomerism

(d) ionization isomerism 1

5. The strongest acid among the following aromatic
compounds is

(a) o-nitrophenol

(b) p-chlorophenol

(c) p-nitrophenol

(d) m-nitrophenol 1

HS/XII/Sc/Ch/24/30 [ P.T.O.

( 4 )

SECTION—B
( Marks : 14 )

6. Either

(a) Show that the half-life period of a first-order reaction
is independent of the initial concentration of the
reactant. 2

Or

(b) A first-order reaction has a rate constant of
10 -3 sec -1. How much time will it take for 10 g
of the reactant to reduce to 2·5 g?

7. (a) When does average rate become equal to
instantaneous rate? 1

(b) Write any one condition under which a bimolecular
reaction may kinetically become first order. 1

8. Either

(a) Why are Mn2+ compounds more stable than
Fe 2+ compounds towards oxidation to their +3 state? 2

Or

(b) Write any two consequences of lanthanoid
contraction. 2

9. Either

(a) Give one example of a complex showing linkage
isomerism. 1

HS/XII/Sc/Ch/24/30 [ Contd.

( 5 )

(b) Write the IUPAC name of the complex
[Cr (NH 3 )3 (H2O)3 ]Cl 3 . 1

Or

(c) Explain, on the basis of valence bond theory,
why [NiCl4 ] 2- is paramagnetic while [Ni (CO)4 ] is
diamagnetic though both are tetrahedral. 2

10. Either

(a) Name the reagent(s) used in the following
conversions : 1+1=2

(i) Ethanoic acid to ethanol

(ii) Bromination of phenol to 2,4,6-trinitrophenol

Or

(b) How would you convert methyl magnesium bromide
to 2-methyl propan-2-ol? 2

11. (a) Name two components of starch. 1

(b) Which vitamin deficiency causes poor coagulation
of blood? 1

12. (a) What do you mean by glycosidic linkage? 1

(b) Write the structure of product formed when
D-glucose is treated with NH2OH. 1

HS/XII/Sc/Ch/24/30 [ P.T.O.

( 6 )

SECTION—C
( Marks : 36 )

13. Either
(a) Give one example of a solution showing positive
deviation from Raoult’s law. 1
(b) The vapour pressure of pure benzene at certain
temperature is 0·850 bar. A non-volatile non-
electrolyte solute weighing 0·5 g is added to 39 g
of benzene. The vapour pressure of the solution is
0·845 bar. What is the molar mass of the solute
added? (Given, molar mass of benzene = 78 g mol -1) 2

Or

(c) What are azeotropic mixtures? 1
(d) Calculate the mole fraction of ethylene glycol
(C2H 6O2 ) in an aqueous solution containing 20%
of ethylene glycol by mass. 2

14. (a) What are isotonic solutions? 1
(b) A solution is prepared by dissolving 60 g of glucose
(C 6H12O 6 ) in 250 g of water. Calculate the freezing
point of the solution. (K f for H2O = 1 × 86 K kg mol -1) 2

15. Either

(a) What is the difference between electrochemical cell
and electrolytic cell? 1
(b) Why does a dry cell become dead after a long time
even if it has been not in use? 1
(c) What is cathodic protection? 1

HS/XII/Sc/Ch/24/30 [ Contd.

( 7 )

Or

(d) When a current of 0·75 A is passed through
CuSO4 solution for 25 minutes, 0·369 g of copper
is deposited at the cathode. Calculate the atomic
mass of copper. (F = 96500 C mol -1) 2

(e) Write the products of electrolysis of NaCl (aq)
solution. 1

16. (a) What is the order of a reaction whose rate constant
has same unit as the rate of reaction? 1

(b) The rate constants of a reaction at 500 K and
700 K are 0·02 s -1 and 0·07 s -1 respectively.
Calculate the activation energy of the reaction.
(R = 8 × 314 J K -1 mol -1) 2

17. (a) What is crystal field splitting energy? 1

(b) Write the coordination number and oxidation state
of Pt in the complex [Pt (en)2 Cl2 ] . 1

(c) Name the type of hybridization of central metal atom
in the complex [Fe (H2O)6 ] 2+ . (Given atomic number
of Fe = 26) 1

18. Either

(a) Arrange the following compounds in order of their
increasing boiling points : 1
Bromomethane, Bromoform, Chloromethane,
Dibromomethane

HS/XII/Sc/Ch/24/30 [ P.T.O.

( 8 )

(b) Identify A, B and R in the given sequence of
reactions : 2
CH3 CH3
Na/ether
H3C CH3 R—X
CH3 CH3 Mg
H2O
B A
Or

(c) Arrange the following compounds in order of their
reactivity towards SN 2 reaction : 1
2-bromo-2-methylbutane, 1-bromobutane,
2-bromobutane

(d) How would you convert 1-bromopropane to butanoic
acid? 2

19. Complete the following reactions : 1×3=3
CH3
(i) + HI ?

CH2OH
(ii) + HCl ?
HO

Ethanol
(iii) CH3CH2Br + AgCN ?

20. Either

(a) Write the chemical equation for Kolbe’s reaction. 1

(b) Give the mechanism of acid catalyzed hydration
of ethene. 2

HS/XII/Sc/Ch/24/30 [ Contd.

( 9 )

Or

(c) Complete the following reactions : 1×3=3
O
CH2—C—OC2H5
NaBH4
(i) O ?

OC2H5
(ii) + HBr ?

OH

Na2Cr2O7/H2SO4
(iii) ?

21. (a) Arrange the following in increasing order of their
acidic character : 1
HCOOH, CF3COOH, ClCH2COOH, CCl 3COOH
(b) How would you obtain the following? 1+1=2

(i) Benzoic acid from ethyl benzene

(ii) Butanoic acid from 1-chlorobutane

22. (a) Why do amines act as nucleophiles? 1

(b) How would you convert ethanoic acid into
methanamine? 2

23. (a) Name a test to distinguish between aniline and
N-methylaniline. 1

(b) Complete the following reactions : 1×2=2
CuCN
(i) C6H5N2Cl ?

LiAlH4
(ii) C6H5CN ?

HS/XII/Sc/Ch/24/30 [ P.T.O.

( 10 )

24. (a) What are nucleotides? 1

(b) What are essential and non-essential amino acids?
Give one example of each type. 2

SECTION—D
( Marks : 15 )

25. Either

(a) Represent the cell in which the following cell reaction
takes place :

Zn (s) + 2Ag + (aq) ¾¾® Zn2 + (aq) + 2Ag (s)
Which one of the electrodes is negatively
charged? 1+1=2

(b) State Kohlrausch’s law. 1

(c) Calculate the molar conductivity of Al 3+ ions at
infinite dilution. Given that the molar conductivity
of Al2 (SO4 )3 and ionic conductivity of SO2-
4 ion
at infinite dilution are 858 S cm 2 mol -1 and
160 S cm 2 mol -1 respectively. 2

Or

(d) What is electrochemical series? 1

(e) Why is it necessary to use salt bridge in a galvanic
cell? 1

HS/XII/Sc/Ch/24/30 [ Contd.

( 11 )

(f) Arrange the following metals in increasing order of
their reducing power :
Zn, Ag, Ni, Cu
Given :
o o
E Zn 2+
/Zn
= - 0 × 76 V, E Ag +
/Ag
= + 0 × 80 V,

o o
E Ni 2+
/Ni
= - 0 × 25 V, E Cu 2+
/Cu
= + 0 × 34 V 1

(g) The cell potential for the cell reaction

Zn (s) + Cu2 + (1 × 0 M ) ¾¾® Zn2 + (0 × 1 M ) + Cu (s)
is 1·30 V at 25 °C . Calculate its standard cell
potential. 2

26. Either

(a) Why do transition elements show variable oxidation
states? 1

(b) Why are Zn2+ salts white whereas Cu2+ salts are
coloured? 1

(c) Draw the structure of a permanganate ion (MnO4- ). 1

(d) Give the reactions of KMnO4 with KI and FeSO4 in
acidic medium. 1+1=2

Or

(e) Write the highest oxidation state shown by an
element with atomic number 23. 1

(f) What do you mean by disproportionation reaction?
Give one example. 1+1=2

HS/XII/Sc/Ch/24/30 [ P.T.O.

( 12 )

(g) Give reasons for the following : 1+1=2
(i) Transition metals and their compounds
generally exhibit paramagnetic behaviour.
(ii) Manganese exhibits the highest oxidation state
of +7 among 3d series of transition elements.

27. Either
(a) Arrange the following compounds in increasing
order of their reactivity in nucleophilic addition
reactions : 1
Ethanal, Propanal, Butanone, Propanone
(b) Identify the compounds A and B in the following
sequence of reactions : 2
SOCl2 H /Pd/BaSO4 / S
CH 3CH2COOH ¾ ¾ ¾ ¾ ¾® A ¾ ¾2¾ ¾ ¾ ¾ ¾ ¾ ¾® B
(c) Give the products of the following reactions : 1×2=2
NH2—NH2
(i) CH3CH2CH2CHO ?
D
Anhydrous AlCl3
(ii) + C6H5COCl ?
CS2
Or

(d) Name the test to distinguish between propanal and
propanone. 1
(e) How would you convert ethanal into but-2-enal in
not more than two steps? 2
(f) Write the structures of A and B in the following
sequence of reactions : 2
LiAlH4 conc. H SO / D
CH 3COCH 3 ¾ ¾ ¾ ¾ ¾® A ¾ ¾ ¾ ¾ 2¾ ¾4¾ ¾® B

HHH

HS/XII/Sc/Ch/24/30 24K—5380

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