Class 11 Question Paper 2025 Chemistry

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SESSION ENDING EXAMINATION 2024-25
CLASS: XI ​ ​ ​ ​ ​ ​ ​ ​ SUBJECT: CHEMISTRY
TIME: 3 HOURS​ ​ ​ ​ ​ ​ ​ ​ M. MARKS: 70

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 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.

Q No Section-A (16x1 = 16 marks) Marks

1 Which of the following has the highest mass? 1
a)​ 1 mole of O₂
b)​ 1 mole of H₂O
c)​ 1 mole of CO₂
d)​ 1 mole of CH₄

2 If 4 g of dihydrogen reacts with 16 g of dioxygen to form water, what is 1
the mass of water formed?
(a) 32 g b) 36 g c) 18 g d) 20 g

3 The Correct order of size of the given species?​ 1
(a) I+ > I- > I​
- +
(b) I > I > I​
(c) I- > I > I+ ​
(d) I > I+ > I-

4 The type of hybridization in ammonia (NH₃) is:​ 1
a) sp b) sp² c) sp³ d) sp³d

5 If the concentration of a reactant is decreased in a system at equilibrium, 1
the equilibrium will shift:
a) To the left, favouring the reactants​
b) To the right, favouring the products​
c) No shift will occur​
d) The equilibrium will be disturbed and no shift will happen.

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6 When a solution of sodium acetate is added to a solution of acetic acid, the 1
ionization of acetic acid is suppressed. This phenomenon is an example of
a) Le Chatelier’s Principle​
b) Common Ion Effect​
c) Dynamic equilibrium​
d) Van't Hoff factor

7 What is the oxidation number of aluminium in LiAlH4​? 1
a) +1 b) +3 c) -5 d) 0

8 What is the IUPAC name of CH₃-O-CH₂CH₃? 1
a) Ethyl methyl ether​
b) Methoxyethane​
c) Methyl Ethyl ether​
d) Ethoxymethane

9 Which of the following is true for an adiabatic process? 1
a) q=0 b) ΔS=0 c) PV=constant d) T is constant

10 Which of the following statements is correct? 1
a) ΔG>0, the process is spontaneous.
b) ΔG=0, the system is at equilibrium.​
c) ΔG<0, the process is non-spontaneous.
d) ΔH>0, the process is always spontaneous.

11 The addition of HCl to propene in presence of peroxide, the major product 1
is:
a) 1-Chloropropane b) 2-Chloropropane c) Propane d)
3-Chloropropane

12 Which of the following statements is correct about the Wurtz reaction? 1
a) It is used to prepare alkenes by the reaction of alkyl halides with sodium
metal in ether.​
b) It is used to prepare alkanes by the reaction of alkyl halides with
sodium metal in ether.​
c) It is used to prepare alcohols by the reaction of aldehydes with Grignard
reagents.​
d) It is used to prepare alkynes by the reaction of alkyl halides with
sodium metal.

13 Assertion (A): The 4s orbital is filled before the 3d orbital.​ 1
Reason (R): The energy of the 4s orbital is lower than that of the 3d
orbital.
(a) Both Assertion and Reason are correct, and Reason is the correct
explanation of Assertion.
(b) Both Assertion and Reason are correct, but Reason is not the correct
explanation of Assertion.
(c) Assertion is correct, but Reason is incorrect.
(d) Assertion is incorrect, but Reason is correct.

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14 Assertion (A): The bond angle in the water molecule (H₂O) is 104.5°. 1
Reason (R): The water molecule has two lone pairs of electrons on
oxygen, which cause repulsion and reduce the bond angle.
(a) Both Assertion and Reason are correct, and Reason is the correct
explanation of Assertion.
(b) Both Assertion and Reason are correct, but Reason is not the correct
explanation of Assertion.
(c) Assertion is correct, but Reason is incorrect.
(d) Assertion is incorrect, but Reason is correct.

15 Assertion (A): The IUPAC name of C₆H₅OH is Benzyl alcohol.​ 1
Reason (R): The presence of an -OH group on a benzene ring is called
phenol in IUPAC nomenclature.
(a) Both Assertion and Reason are correct, and Reason is the correct
explanation of Assertion.
(b) Both Assertion and Reason are correct, but Reason is not the correct
explanation of Assertion.
(c) Assertion is correct, but Reason is incorrect.
(d) Assertion is incorrect, but Reason is correct.

16 Assertion (A): Lower alkanes (C1 to C4) exist as gases at room 1
temperature.
Reason (R): The boiling points of alkanes increase with an increase in
molecular weight due to Van der Waals forces.
(a) Both Assertion and Reason are correct, and Reason is the correct
explanation of Assertion.
(b) Both Assertion and Reason are correct, but Reason is not the correct
explanation of Assertion.
(c) Assertion is correct, but Reason is incorrect.
(d) Assertion is incorrect, but Reason is correct.

Section-B (5x2 = 10 marks)

17 Write the main postulates of Dalton’s atomic theory. 2

18 State Modern periodic law and Mendeleev’s periodic law. 2

19 The pKa of acetic acid and the pKb of ammonium hydroxide are 4.76 and 2
4.75 respectively. Calculate the PH of ammonium acetate solution.
OR
H -8
Calculate the P of 1 X 10 M HCl solution at 298 K assuming complete
dissociation. (log 1.1 = 0.0414 log 10 =1 )

20 Define Hyperconjugation and Inductive effect. 2

21 An alkene on ozonolysis gives ethanal only . Write the structure and 2
IUPAC name of alkene.

Section - C (7x3 = 21 marks)

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22 A compound contains 4.07 % hydrogen ,24.27% carbon and 71.65 % 3
chlorine. Its molar mass is 99 g. What are Its empirical and molecular
formulas?
Or

Chlorine is prepared in the laboratory by treating manganese dioxide
(MnO2) with aqueous hydrochloric acid according to the reaction:

4HCl (aq) + MnO2(s) → 2H2O(l) + MnCl2(aq) + Cl2(g)

How many grams of HCl react with 5.0 g of manganese dioxide?
(Molar mass of Mn =55g/mol Cl=35.5 g/mol)

23 (a)​ Write the four quantum numbers for the unpaired electron of 3
Chlorine atom (Cl , Z = 17).
(b)​Write Name & the rule due to which following electronic
configuration for Nitrogen is not possible.

24 Interpret the graph and answer the following. 3 (1+2)

a)​ Why is the first ionization energy of nitrogen more than that of
oxygen?
b)​ Arrange the following elements in increasing order indicated
properties.
i.​ Li, Be, B, C ( First Ionisation Enthalpy)
ii.​ Li, Be, B, C ( Metallic Character )

25 .(a) Define entropy. 3
(b) Predict in the following process, entropy increases/decreases:
​ H2 (g) → 2H(g)
2NaHCO3 (s) → Na2CO3 (s) + CO2 (g)+ H2O (g)

26 a)​ Write the conjugate acid and conjugate base of ammonia. 3 (1+2)
b)​ Derive the relationship Kp= Kc (RT)∆n

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27 Permanganate ion reacts with bromide ion in basic medium to give 3
manganese dioxide and bromate ion. Write the balanced ionic equation for
the reaction.

28 a)​ Why is an isomeric tertiary carbocation more stable than a primary 3
carbocation?
b)​ Out of formic acid and acetic acid which is more acidic & why?
c)​ Why is But -2-ene more stable than But-1-ene?

Section - D (2x4 = 8 marks)
The following questions are case-based questions. With internal choice in
one question of both case based study question and carries 4 (2+1+1)
marks each.

29 A student is tasked with determining the enthalpy of formation of methane
CH₄(g) using Hess's Law. To do this, the student gathers the following
information about the enthalpy of combustion of methane, graphite (solid
carbon), and hydrogen gas at 298 K:

●​ Enthalpy of combustion of methane (CH₄(g)): –890 kJ/mol
●​ Enthalpy of combustion of graphite (C): –393 kJ/mol
●​ Enthalpy of combustion of hydrogen (H₂): –286 kJ/mol

The student understands that the enthalpy of formation of a substance is
the enthalpy change when one mole of the substance is formed from its
elements in their standard states. In the case of methane, the elements are
carbon (graphite) and hydrogen (H₂), and the formation reaction is:
C(s)+2H2(g)→CH4(g)
Using Hess's Law, which states that the total enthalpy change for a
reaction is the sum of the enthalpy changes for the steps that lead to that
reaction, the student reverses the combustion reactions of methane,
graphite, and hydrogen to achieve the formation of methane from its
elements.
Based on above paragraph answer the following.
(a)​ The enthalpy of combustion of methane, graphite and dihydrogen 2
at 298 K are, –890 kJ mol–1 , –393 kJ mol–1, and –286 kJ mol–1
respectively. Calculate the enthalpy of formation of CH4(g).
OR
For a reaction at 298 K 2 A + B →C ∆H = 400 kJ mol -1
and ∆S = 0.02 kJ K-1 mol -1.At what temperature will the reaction
become spontaneous considering ∆H and ∆S to be constant over
the temperature range ?
(b)​Which of following has/have zero enthalpy under standard 1
conditions?
1)​ CH4(g) 2)O2 (g) 3)CO2 (g) 4)H2O (l)
(c ) State Hess’s law of constant heat of summation. 1

30 In the field of organic chemistry, determining the elemental composition of
compounds is crucial for understanding their structure and reactivity. Two

Annual Exam 2025 Question Paper
well-known methods used for this purpose are the Carius method and the
Dumas method.
The Carius method is primarily used for determining the percentage of
halogens (like chlorine, bromine, and iodine) in organic compounds. In
this method, a known mass of the organic compound is placed in a sealed
tube along with excess fuming nitric acid and sodium or potassium
chlorate . The sealed tube is then heated. The halogen in the compound
reacts with the chlorate to form a halogenated acid, which is then
separated and analysed to determine the amount of halogen present in the
sample. The amount of halogen is calculated based on the volume of the
halogenated acid formed.
The Dumas method, on the other hand, is a technique used for determining
the nitrogen content in organic compounds. This method involves heating
a known mass of the compound in a combustion tube with excess copper
oxide (CuO) in the presence of oxygen. The nitrogen in the compound is
oxidized to nitrogen gas (N₂), which is collected and measured. The
volume of nitrogen gas obtained is then used to calculate the percentage of
nitrogen in the compound. This method is particularly useful for
determining nitrogen content in organic compounds such as proteins and
amines.
Both methods are widely used in qualitative analysis for determining the
elemental composition of organic compounds. While the Carius method is
specific to halogens, the Dumas method is commonly used for nitrogen,
helping chemists in the analysis of complex organic molecules.
Based on above paragraph answer the following.
( a) In Carius method of estimation of halogen 0.15 g of an organic 2
compound gave 0.12g of AgBr . Find out the percentage of bromine in the
compound.
OR
0.26 g of an organic compound gave 0.39 g of water and 0.245 g of
carbon dioxide on combustion. Find out the percentage of C and H in the
organic compound .
(b) In the Dumas method for determining nitrogen content, the nitrogen in 1
the organic compound is oxidized to which of the following gases?
a) Ammonia b) Nitrogen dioxide c) Dioxygen d) Nitrogen
gas
( c) Which of the following element is not estimated by Carius method? 1
(a)​ Sulphur (b)Nitrogen (c)Phosphorous
(d)Halogen

Section - E (3x5 = 15 marks)

31 a)​ Write four quantum numbers of 11th electron of Na atom. 2
b)​ Calculate number of radial nodes in 4s orbital. 1
c)​ Calculate the wavelength of an electron moving with a velocity of 2
2.0 × 10⁶ m/s. (Mass of electron = 9.11 × 10⁻³¹ kg, Planck’s
constant h = 6.626 × 10⁻34 Js).
OR
2

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a)​ Write the electronic configuration of​
(a) Cu ( Z=29) (b) Fe3+ ( Z=26) 1
b)​ Explain why Cu (Z = 29) and Cr (Z = 24) show anomalous
electronic configurations. 2
c) Using the quantum mechanical model, determine the total number
of electrons that can be present in the following quantum states:​
a) n=3 l=1 b) n=4 l=2

32 Calculate No. of sigma and pi bond in following: 2
a)​ (i) CH2 = CH – CHO (ii) CH3COOCH3
b)​ Write the electronic configuration of F2 + based on MOT. 1
c)​ Which out of NH3 and NF3 has higher dipole moment and why? 1
d)​ Draw the shapes of sp, sp2 hybrid orbitals. 1
OR
a)​ Define the term bond order. Calculate the bond order of O2 & 3
O2+ .
b)​ What is the hybrid state of : 2
(i) S in SF4 (ii) C in CO2 ?, Also draw the geometry of each molecule
according to VSEPR theory.

33 Write all possible structures and IUPAC names of different structural 5
isomers of alkenes corresponding to C5H10 .
OR
(i)​ Convert
a)​ Benzene to Cyclohexane
b)​ Benzene to Toluene
c)​ Benzene to Nitrobenzene
(ii)​ Write chemical equations for combustion reaction of the
following hydrocarbons:
(a)​ Methane
(b)​Butane

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SESSION ENDING EXAMINATION 2024-25

CLASS XI
CHEMISTRY THEORY (043)
Max. Marks:70 Time: 3 hours
Model Answer Sheet
1 C - 1 mole of CO₂ 1
2 C- 18 g 1
3 C- I- > I > I+ 1
4 C- sp³ 1
5 A To the left, favouring the reactants 1
6 B Common Ion Effect 1
7 B +3 1
8 B- Methoxyethane 1
9 A q=0 1
10 B ΔG=0, the system is at equilibrium. 1
11 B 2-Chloropropane 1
12 B It is used to prepare alkanes by the reaction of alkyl halides with sodium 1
metal in ether.
13 (A) Both Assertion and Reason are correct, and Reason is the correct 1
explanation of Assertion.
14 (A) Both Assertion and Reason are correct, and Reason is the correct 1
explanation of Assertion.
15 D- Assertion is incorrect, but Reason is correct. 1
16 (A) Both Assertion and Reason are correct, and Reason is the correct 1
explanation of Assertion.
17 ●​ Matter is composed of indivisible particles called atoms. 1/
●​ Atoms cannot be created, divided, or destroyed in a chemical reaction. 2x
●​ All atoms of a specific element are identical in mass and properties. 4=
●​ Atoms of different elements differ in their mass and chemical 2
properties.
●​ Compounds are formed when atoms of different elements combine in
fixed, simple, whole number ratios.
●​ Chemical reactions involve the rearrangement of atoms, without any
change in the atoms themselves.
18 Mendeleev's Periodic Law: The physical and chemical properties of 1,1
elements are periodic functions of their atomic masses.

Modern Periodic Law: The physical and chemical properties of elements
are periodic functions of their atomic numbers.
19 2

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Or

20 ●​ Hyperconjugation is the delocalization of electrons in sigma bonds 2
(usually C-H ) to an adjacent empty or partially filled p-orbital .

●​ The inductive effect is the polarization of the electron density along a
carbon chain of atoms in a molecule or ion due to the electronegativity
of substituents. It is a permanent effect and affects the distribution of
electron density through sigma bonds.
21 ●​ CH₃-CH=CH-CH₃ 2
●​ But-2-ene
22 Empirical and Molecular Formula Calculation
Given percentages:
●​ Hydrogen (H) = 4.07%
●​ Carbon (C) = 24.27%
●​ Chlorine (Cl) = 71.65%
●​ Molar mass = 99 g/mol
Moles of H = 4.07/1 ​=4.07

Moles of C = 12.27/12= 2.02

Moles of Cl = 71.65/36.5= 2.02

Divide by the smallest number of moles
H = 4.07/2.02 ​ approx 2
C = 2.02/2.02= approx 1
Cl = 2.02/2.02= approx 1

●​ Empirical Formula: CH₂Cl
𝑀𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠
𝑛 = 𝐸𝑚𝑝𝑖𝑟𝑖𝑐𝑎𝑙 𝑓𝑜𝑟𝑚𝑢𝑙𝑎 𝑚𝑎𝑠𝑠

●​ Molecular Formula = n x Empirical Formula= 2 x CH₂Cl
●​ Molecular Formula = C₂H₄Cl₂

OR

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4HCl + MnO2​→2H2​O+MnCl2​+Cl2​

Molar mass of MnO2 = ( 55 + 32)= 87 g/mol

Molar mass of HCl = ( 1 + 35.5)= 36.5 g/mol

From above chemical reaction

87 g of MnO2 reacts with (4 x 36.5) g of HCl

Therefore 5 g of MnO2 will react with (4 x 36.5) X 5/87 g of HCl
4 𝑥 36.5 𝑋 5
𝑀𝑎𝑠𝑠 𝑜𝑓 𝐻𝐶𝑙 = 87

𝑀𝑎𝑠𝑠 𝑜𝑓 𝐻𝐶𝑙 = 8. 39 𝑔

23 (a) For the unpaired electron of Cl (Z = 17):

●​ Principal quantum number (n): 3
●​ Azimuthal quantum number (l): 1
●​ Magnetic quantum number (ml): +1
●​ Spin quantum number (ms): +1/2

(a)​ Hund’s Rule :: In a degenerate set of orbitals pairing of electrons
cannot take place until all the orbitals are singly filled.
24 a)​ Half -filled configuration
b)​ First Ionisation Enthalpy: Li < B < Be < C
c)​ Metallic Character: C < Be < B < Li
25 (a) Entropy: It is a measure of the disorder or randomness in a system.
(b) Entropy changes:
H2(g)→2H(g) Increases
●​ 2NaHCO3(s)→Na2CO3(s)+CO2(g)+H2O(g) Increases
26 Conjugate acid of ammonia is NH4+ Conjugate base of ammonia is NH2−
(b)

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27

28 (a) Tertiary carbocation is more stable than primary due to more
hyperconjugation and inductive effects.

(b) Formic acid (HCOOH) is more acidic than acetic acid (CH3COOH)
because the -H group is less electron-donating than the -CH3 group.

(c) But-2-ene is more stable than But-1-ene due to the greater
hyperconjugation and alkyl group stabilization.
29 ( a ) CH4(g) + 2 O2(g) → CO2+ 2 H2O(l) ΔH = -890 kJ/mol 2+
1+
C(s) + O2(g) → CO2(g) ΔH = -393 kJ/mol 1

2 H2(g) + O2(g) → 2 H2O ΔH = (-286x2) kJ

To find the enthalpy of formation of CH4(g), we use the reverse reaction for
the formation of CH4(g) from its elements:

C(s) + 2 H2(g) → CH4(g)

Now ,first, we reverse the combustion reaction of methane to obtain the
formation reaction:

CO2 + 2 H2O(l) → CH4(g) + 2 O2(g) ΔH = +890 kJ/mol

Now, we add the enthalpy changes of the reversed methane reaction and the
combustion reactions of graphite and dihydrogen:

ΔH = +890 kJ/mol + (-393 kJ/mol) + 2(-286 kJ/mol)

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ΔH = +890 kJ/mol - 393 kJ/mol - 572 kJ/mol

ΔH = -75 kJ/mol

OR

ΔG=ΔH−TΔS

Assuming that equation at equilibrium then ΔG = 0

ΔG=ΔH−TΔS=0

T=ΔH/ΔS=400/.02=20000K

For the reaction to be spontaneous ΔG must be negative. Therefore
temperature should be greater than 20000

(b) O2 (g)

(c)Hess's Law states that the total enthalpy change for a reaction is the same,
no matter how many steps the reaction is carried out in.
30 (a) 2+
1+
1

OR

Percentage of Carbon = 25.69 , Hydrogen = 16.66

(b) Nitrogen gas

(c)option b Nitrogen
31 (a ) n=3 l=0 m=0 s=+1/2 2+
1+
2

(b) 3

( c ) We can calculate the wavelength of the electron using the de
Broglie wavelength formula:

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λ=h/mv
λ=6.626 × 10⁻34./ 2.0 × 10⁶ m/s X 9.11 × 10⁻³¹ kg
λ=3.64×10−10 m

OR
Cu= [Ar] 4s1 3d10
Fe3+ = [Ar] 4s0 3d5
( b ) To acquire extra stability of half-filled and full- filled
configuration.
© (a) 6 (b ) 10
32 a.​ CH₂=CH-CHO Sigma 7 pi 2 CH₃COOCH₃ Sigma 10 pi 1 2
b.​ Electronic Configuration of F2+
σ(1s)² σ*(1s)² σ(2s)² σ*(2s)² σ(2pz)² π(2px)² = π(2py)² π*(2px)² = *(2py)1 1
(c ) NH₃ has a higher dipole moment than NF₃ because in NH₃, the lone pair 1
on nitrogen points in the same direction as the bond dipoles, whereas in NF₃,
the lone pair on nitrogen opposes the bond dipoles.
(d)

1

OR
( a ) Bond Order is the number of chemical bonds between a pair of atoms. 3
Or Half of difference between bonding and antibonding electrons.
O₂: Bond Order= Nb-Na/2
(10-6)/2=2
O₂⁺: Bond Order= Nb-Na/2
(10-5)/2=2.5

( b) S in SF₄:
2
Hybridization: sp³d

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C in CO₂:

Hybridization: sp

Geometry: Linear
33 5

Or

(i)

(a)

(b )

(c)

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(ii)

(a)​

(b)​

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