Class 12 Pre Board Question Paper 2024 Chemistry

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Pre-Board Exam 2024 Question Paper

PRE BOARD-1 (SESSION: 2023-2024)
CHEMISTRY THEORY (043)

MM:70 Time: 3 hours

General Instructions: Read the following instructions carefully.
a) There are 33 questions in this question paper with internal choice.
b) SECTION A consists of 16 multiple-choice questions carrying 1 mark each .
c) SECTION B consists of 5 very short answer questions carrying 2 marks each.
d) SECTION C consists of 7 short answer questions carrying 3 marks each.
e) SECTION D consists of 2 case- based questions carrying 4 marks each.
f) SECTION E consists of 3 long answer questions carrying 5 marks each.
g) All questions are compulsory.
h) Use of log tables and calculators is not allowed

SECTION A
The following questions are multiple-choice questions with one correct answer. Each question carries 1
mark. There is no internal choice in this section .

1. Which of the following will give Aldol condensation?
(a) CH3CHO
(b) (CH3)3CCHO
(c) HCHO
(d) C6H5CHO

2 .KMnO4 is coloured due to -
(a) d-d transition
(b) charge transfer from ligand to metal
(c) unpaired electron in d orbital of Mn
(d) charge transfer from metal to ligand

3. Which of the following solutions will have the highest conductivity at 298 K ?
(a) 0.01 M HCl solution
(b) 0.01 M CH3COOH solution
(c) 0.1 M CH3COOH solution
(d) 0.1 M HCl solution

4. When benzene diazonium chloride reacts with phenol , it forms a dye . This reaction is called -
(a) Diazotisation .
(b) Coupling reaction
(c) Alkylation reaction
(d) Condensation reaction

5. What would be the major product of the following reaction ?
C6H5-CH2-O-C6H5 + H-Br → A + B
(a) A = C6H5CH2OH , B= C6H6
(b) A = C6H5CH2OH , B= C6H5Br

(c) A = C6H5CH3 , B= C6H5Br
(d) A = C6H5CH2Br , B= C6H5OH

6.Which of the following is the strongest base in aqueous solution ?
(a) NH3
(b) CH3NH2

(c) (CH3)2NH
(d) (CH3)3NH

7.Which of the following is a diamagnetic ion (atomic no of Sc ,V, Mn and Cu are 21,23,25 and 29
respectively )
(a) V2+
(b) Sc3+
(c) Cu2+
(d) Mn2+

8. The main product formed when phenol is heated with conc.nitric acid -
(a) o- Nitro phenol
(b) Benzene
(c) Picric acid
(d) Methoxy benzene

9. Hydrolysis of sucrose is called -
(a) Inversion
(b) Hydration
(c) Esterification
(d) Saponification

10.The rate constant , the activation energy and the Arrhenius parameter of a chemical reaction at 250C
are 3.0 x 10-4 s-1 , 104.4 KJ mol-1 and 6.0 x1014 s-1 respectively .The value of rate constant as T→ ∞ is
(a) 2.0x1018 s-1
(b) 6.0 x1014 s-1
(c) infinity
(d) 3.6 x1030 s-1

11. The IUPAC name of iso butyl bromide is -
(a) 1- Bromo -3- methyl butane
(b) 3- Bromo -2- methyl propane
(c) 2- Bromo -2- methyl propane
(d) 1- Bromo -2- methyl propane

12.For the given rate expression -
r = K [A] [B] , the unit of rate constant is
(a) mol-1 L s-1
(b) mol-1 L s
(c) mol-1 L-1
(d) mol-2 L s-2

13. Given below are two statements labelled as Assertion (A) and Reason (R)
Assertion (A): Nitric acid and water form maximum boiling azeotrope .
Reason (R) : Azeotropes are binary mixture having the same composition in liquid and vapour phase .
Select the most appropriate answer from the options given below:
a. Both A and R are true and R is the correct explanation of A
b. Both A and R are true but R is not the correct explanation of A.

c. A is true but R is false.
d. A is false but R is true.

14. Given below are two statements labelled as Assertion (A) and Reason (R)
Assertion (A) : N-Ethylbenzene sulphonamide is soluble in alkali.
Reason (R) : Hydrogen attached to nitrogen in sulphonamide is strongly acidic .

Select the most appropriate answer from the options given below:
a. Both A and R are true and R is the correct explanation of A
b. Both A and R are true but R is not the correct explanation of A.
c. A is true but R is false.
d. A is false but R is true.

15. Given below are two statements labelled as Assertion (A) and Reason (R)
Assertion (A): Alcohols react both as nucleophiles and electrophiles.
Reason (R): The bond between C–O is broken when alcohols react as nucleophiles
Select the most appropriate answer from the options given below:
a. Both A and R are true and R is the correct explanation of A
b. Both A and R are true but R is not the correct explanation of A.
c. A is true but R is false.
d. A is false but R is true.

16. Given below are two statements labelled as Assertion (A) and Reason (R)
Assertion (A): [Ti(H2O)6]3+ is coloured while [Sc(H2O)6]3+ is colourless .
Reason (R): d-d transition is not possible in [Sc(H2O)6]3+ .
Select the most appropriate answer from the options given below:
a. Both A and R are true and R is the correct explanation of A
b. Both A and R are true but R is not the correct explanation of A.
c. A is true but R is false.
d. A is false but R is true.

SECTION B

This section contains 5 questions with internal choice in one question. The following questions are very
short answer type and carry 2 marks each.

17. Calculate the mass of ascorbic acid (vitamin C , C6H8O6) to be dissolved in 75 g of acetic acid to
lower its freezing point by 1·5°C. ( Kf for CH3COOH = 3·9 K kg mol-1)

18(a) The conversion of molecule A to B follow second order kinetics .If concentration of A is increased
to three times , how will it affects the rate of formation of B ?
(b) Define pseudo first order reaction with an example .

19. Draw the structure of major monohalogen product formed in the following reactions -
(a)

(b)

20. Arrange the following compounds in an increasing order of their property as indicated :
(a) Acetaldehyde , Acetone , Methyl tert-butyl ketone (reactivity towards HCN)
(b) CH3CH2CH (Br) COOH , CH3CH (Br) CH2COOH , (CH3)2CHCOOH (acidic strength )
or

Write the reactions involved in the following reactions –
(a) Clemmensen reduction
(b) Cannizzaro reaction

21. What happens when D – glucose is treated with the following reagents -
(a) Bromine water
( b) HI

SECTION C
This section contains 7 questions with internal choice in one question. The following questions are short
answer type and carry 3 marks each.

22 (a) Give two differences between order and molecularity of reaction .
(b) A first-order reaction takes 69.3 min for 50% completion. What is the time needed for 80% of the
reaction to get completed? (Given: log 5 =0.6990, log 8 = 0.9030, log 2 = 0.3010 )
or
(a) Define Activation energy.
(b) The rate of chemical reaction doubles for an increase of 10K in absolute temperature from 298 K
.Calculate Ea .(R=8.314 JK-1 mol-1

23. Account for the following -
(a) Ethylamine is soluble in water whereas aniline is not.
(b) Although amino group is o and p – directing in aromatic electrophilic substitution reactions, aniline on
nitration gives a substantial amount of m- nitroaniline.
(c) Aniline does not undergo Friedel -Crafts reaction.

24. (a) Draw all the isomers (geometrical and optical) of – [ Co Cl2(en)2]+
(b) How does the magnitude of ∆o decide the actual configuration for d5 orbitals in a coordination
entity ?

25 .What happens when –
(a) Anisole is treated with CH3Cl /anhydrous AlCl3 .
(b) Phenol is oxidized with Na2Cr2O7/H+
(c) (CH3)3C-OH is heated with Cu /573K .
Write chemical equation in support of your answer .

26.(a) When a co-ordination compound CrCl3.6H2O is mixed with AgNO3, 3 moles of AgCl are
precipitated per mole of the compound . Write
(i) Structural formula of the complex
(ii) IUPAC name of the complex
(b) Write the state of hybridization and the shape of the following complex entities : K2[Ni(CN)4]

27. Give reason for the following –
(a) Chloroform is stored in closed dark brown bottles.
(b) (±) Butan-2-ol is optically inactive .
(c) C-X bond length in haloarenes is smaller than C-X bond length in haloalkanes .

28. State Kohlrausch law of independent migration of ions. How molar conductivity varies for weak and

strong electrolytes on dilution?

Section D

The following questions are case-based questions. Each question has an internal choice and carries 4
(1+1+2) marks each. Read the passage carefully and answer the questions that follow.

29. Osmosis plays a significant role in the absorption of water by plant roots from the soil and its
movement to different parts of the plant body. When placed in water containing more than 0.9%
(mass/volume) salt, blood cells collapse due to loss of water by osmosis. In animals’ circulation of water
to all parts of the body takes place due to osmosis. Osmosis helps in plant growth and germination of
seeds. The phenomenon of osmosis is also useful in some industrial processes. It is employed
commercially for the desalination of seawater so that it may become useful for drinking purposes.
(Reverse osmosis)The Reverse Osmosis process is very popular for the purification of drinking water in
households.
The osmotic pressure of a solution is the excess pressure that must be applied to a solution to prevent
osmosis, i.e., to stop the passage of solvent molecules through a Semipermeable membrane into the
solution. Osmotic pressure is colligative property as it depends on the number of solute molecules and
not on their identity . For dilute solutions, it has been found experimentally that osmotic pressure is
proportional to the molarity, C of the solution at a given temperature T. Thus: π = CRT Here π is the
osmotic pressure and R is the gas constant .

Answer following questions:
(a) What is reverse osmosis ?
(b) Name the membrane used in Reverse osmosis .
(c)What do you expect to happen when Red blood corpuscles (RBC’s) are placed in –
(i) 1% NaCl solution (ii) 0.5% NaCl solution
or
(c) Measurement of osmotic pressure method is preferred for the determination of molar mass of
macromolecules .Why ?

30. Protein primary structure is the linear sequence of amino acids in a peptide or protein. In contrast,
Secondary structure refers to regular, recurring arrangements in the space of adjacent amino acid residues
in a polypeptide chain. It is maintained by hydrogen bonds between amide hydrogens and carbonyl
oxygens of the peptide back bone. The major secondary structures are α-helix and β- pleated structures.
The tertiary structure of protein represents overall folding of secondary structure. Two major type
molecular shapes which are found naturally are fibrous and globular. Protein found in a biological system
with a unique three-dimensional structure and biological activity is called a native protein . When a
protein in its native form, is subjected to physical changes like change in temperature or chemical changes
like change in pH, the hydrogen bonds are disturbed . Due to this , globules unfold and helix get uncoiled
and protein loses its biological activity. This is called denaturation of protein. The denaturation causes
change in secondary and tertiary structures but primary structures remain intact. Examples of denaturation
of protein are coagulation of egg white on boiling , curding of milk, formation of cheese when an acid is
added to milk.

Answer following questions:
(a) What type of bonding helps in stabilizing the α-helix structure of proteins ?
(b) Where does the water present in egg goes after boiling the egg ?
(c) Give two differences between globular and fibrous protein.
or
(c) What is meant by a peptide linkage? Explain with one example .

SECTION E

The following questions are long answer type and carry 5 marks each. All questions have an internal
choice.

31.(a)Write the reaction of anode and cathode during discharging of lead storage battery

(b) Calculate the emf of the following cell at 25 0C.
Mg (s) | Mg2+ (0.1M) || Cu+2(1.0×10 -3M) | Cu(s)
[Given, E°cell = + 2.71V and log 10n = n]
or
(a) What are fuel cells? Explain the electrode reactions involved in the working of H2─O 2fuel cell.
(b) The conductivity of 0.001 mol L-1 solution of CH3COOH is 3.905x 10 -5 S cm -1. Calculate its molar
conductivity and degree of dissociation (α). Given, λ° (H+) = 349.6 S cm 2mol-1 and λ° (CH3COO-) =
40.9 S cm2 mol-1.

32. (a) Give chemical tests to distinguish between the following pairs of compounds .
(i) Ethanal and Propanal (ii) Phenol and Benzoic acid
(b) How will you bring about the following conversions?
(i) Benzoic acid to benzaldehyde
(ii) Ethanal to but-2-enal
(c) Carboxylic acids do not give characteristic reactions of carbonyl group. Explain why?
or
(a) Give chemical tests to distinguish between the following :
(i) Propanal and Propanone (ii) Benzaldehyde and Acetophenone
(b) Complete each synthesis by giving missing reagents or products in the following :

33. Attempt any five of the following:
(a) Which of the following ions will have a magnetic moment value of 1.73 BM. Sc3+, Ti3+, Ti2+, Cu2+,
Zn2+
(b) In order to protect iron from corrosion, which one will you prefer as a sacrificial electrode, Ni or Zn?
Why? (Given standard electrode potentials of Ni, Fe and Zn are -0.25 V, -0.44 V and -0.76 V
respectively.)
(c) The second ionization enthalpies of chromium and manganese are 1592 and 1509 kJ/mol respectively.
Explain the lower value of Mn.
(d) Give two similarities in the properties of Sc and Zn.
(e) What is actinoid contraction? What causes actinoid contraction?
(f) What is the oxidation state of chromium in chromate ion and dichromate ion?
(g) Write the ionic equation for reaction of KI with acidified KMnO4.

MARKING SCHEME
Q.No. EXPECTED ANSWER / VALUE POINTS MARKS
1 a 1
2 b 1
3 d 1
4 b 1
5 d 1
6 c 1
7 b 1
8 c 1
9 a 1
10 b 1
11 d 1
12 a 1
13 b 1
14 a 1
15 c 1
16 a 1
17 1/2
∆Tf = Kf m
1
∆Tf = Kf × WB / MB × WA 1/2

1.5 = 3.9 × WB / 176 × 0.075

WB = 5.08 g

18 1
(a) 9 times 1/2+1/2
19
(b) Correct definition + Correct example
1

1

20 (a) Methyl tert-butyl ketone < Acetone < Acetaldehyde, 1

(b) (CH3)2CHCOOH < CH3CH (Br) CH2COOH <CH3CH2CH (Br) 1
COOH
or

(a)
1

(b)
1

21 1
(a) Glucose gets oxidized to Gluconic acid . 1

(b) n – Hexane is formed .
22 (a) Any two correct differences 1/2 + 1/2

(b) t1/2 =69.3 min
[R]0 = 100
[ R] = 20
t =?
Then K=0.693/ t1/2 1/2
= 0.693/69.3
=0.01

t=2.303/K (log [R]0/[R]) 1/2

= 2.303 / 0.01 log(100/20) 1/2

= 160.97 min 1/2
Or
(a) Correct definition
1
(b)

1/2

1/2

1/2

1/2

23 (a) Ethylamine dissolves in water due to intermolecular H-bonding. 1
However, in case of aniline, due to the large hydrophobic part, i.e.,
hydrocarbon part, the extent of H-bonding is very less therefore aniline
is insoluble in water.
(b) Under strongly acidic condition anilinium ion is formed which is 1
meta directing .
(c) Aniline being a lewis base reacts with lewis acid AlCl3 to form salt 1
.As a result N of aniline acquire positive charge which act as strong
deactivating group for further reaction .

24 1

1

(b) If ∆o > P , t2g5 eg0 1/2
If ∆o < P , t2g3 eg2 1/2

25 (a) Correct reaction 1
(b) Correct reaction 1
(c) Correct reaction 1

26 (a) (i) [Cr (H2O)6] Cl3 1
(ii) Hexaaquachromium (III) chloride 1
(b) Hybridisation – dsp2 Shape – Square planar 1/2 +1/2
27 a) CHCl3 is stored in dark coloured bottles to cut off light because 1
CHCl3is slowly oxidised by air in presence of light to form an extremely
poisonous gas, carbonyl chloride, popularily known as phosgene.
(b) Both enantiomeric forms cancel the optical rotation of each other . 1
(c) Due to +R effect partial double character arises / due to sp2
hybridised C of haloarenes to which halogen is attached . 1

28 The limiting molar conductivity of an electrolyte can be represented as 1
the sum of the individual contributions of the anion and cation of the
electrolyte .
Correct explanation for strong electrolyte 1
Correct explanation for strong electrolyte 1

29
(a) The process of movement of solvent through a semipermeable
membrane from the solution to the pure solvent by applying excess 1
pressure on the solution side is called reverse osmosis.
(b) Cellulose acetate 1
(c) (i) RBC’s will shrink due to plasmolysis .
(ii) RBC’s will swell and even burst due to hemolysis . 1+1
or
because the magnitude of osmotic pressure is large even for very dilute
solution and it can be measured at room temperature . 1+1

30
(a) Hydrogen bonding 1
(b) When egg is boiled ,the protein first undergo denaturation and then
coagulation .The water present in the egg gets absorbed in the 1
coagulated proteins through H – bonding .
(c) Any two correct differences . 1+1
or
Correct definition + Correct example 1+1

31
(a) Anode - Pb + SO42- → PbSO4 + 2e- 1
Cathode – PbO2 + SO42- +4H+ + 2e- → PbSO4 + 2H2O 1

(b)

1/2

1/2

1

or
(a) Galvanic cells that are designed to convert the energy of combustion 1/2+1/2
of fuel directly into electrical energy are called fuel cells . (Ans +
Anode – H2 + 2OH- → 2H2O + 2e- Unit)
Cathode - O2 + 2H2O + 4e- → 4OH-
1

(b) λm = k × 1000 /C
= 3.905 × 10-5 × 1000 /0.001 1/2+ 1/2
= 39.05 S cm2mol-1
1/2
- +
λ°m CH3COOH = λ°m CH3COO + λ°mH
= 40.9 + 349.6 1/2
= 390.5 S cm2mol-1
α = λcm / λ°m 1/2
= 39.05/390.5
= 0.1 1/2

1/2

1/2
’
32 (a) (i) Ethanal on heating with Tollen s reagent form silver mirror or any 1
other correct difference
(ii) Benzoic acid reacts with sodium bi carbonate to give brisk 1
effervescence of CO2 . or any other correct difference .
(b) (i) Correct conversion 1
(ii) Correct conversion 1
(c) This is due to the lone pairs on oxygen atom attached to hydrogen
atom in the -COOH group are involved in resonance and hence making 1
the carbon atom less electrophilic.
or
(a) (i) Propanal on heating with Tollen’s reagent form silver mirror . 1
or any other correct difference .
(ii) Acetophenone on heating with I2 and NaOH form yellow ppt of 1
iodoform . or any other correct difference .

(b) Correct reaction with correct missing reagent or product 1 +1+1

33
(a) Both Ti3+ and Cu2+ have 1 unpaired electron, so the magnetic moment
for both will be 1.73 BM
(b) Zn, it has a more negative electrode potential so will corrode itself in
place of iron.
(c) Mn+ has 3d 54s1 configuration and configuration of Cr+ is 3d5 ,
therefore, ionisation enthalpy of Mn+ is lower than Cr+ .
(d) Sc and Zn both form colourless compound and are diamagnetic.
(e) The decrease in the atomic and ionic radii with increase in atomic
number of actinoids due to poor shielding effect of 5f electrons .
(f) In both chromate and dichromate ion the oxidation state of Cr is +6 (1 each ,
(g) 10I- + 2MnO4 - + 16H+ → 2Mn2+ + 8H2O + 5I2 any 5)

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