ISC Class 11 Chemistry Half Yearly Sample Paper 2025: Download Free PDF

Question No.

Section A– 14 MARKS

1

1. Select and write the correct alternative from the choices given below:

(vi) Assertion: Molality of a solution does not change with temperature.

Reason: Volume of the solution changes with change in temperature.

(a) Both Assertion and Reason are true but Reason is not the correct explanation for Assertion.

(b) Assertion is false but Reason is true.

(c) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

(d) Assertion is true but Reason is false.

(B) Read the passage given below and answer the questions that follow. [2+1=3]

The attractive force which holds the two atoms together is called a chemical bond. A covalent bond is formed by an equal sharing of electrons. A coordinate bond is formed by unequal sharing of electrons. An ionic bond is formed by the transfer of electrons from one atom to another. Octet rule, although very useful but is not universally applicable. According to valence bond theory, a covalent bond is formed by overlapping of half-filled atomic orbitals resulting in a lowering of energy and more stability. Bond order is the number of bonds between atoms in a molecule. The higher the bond order more will be stability and bond dissociation enthalpy but the smaller the bond length. The polarity of a covalent bond depends upon the difference in electronegativity. The covalent character of a bond depends upon polarising power, smaller cation and bigger anions have higher polarising power. VSEPR theory helps to predict the shapes of molecules.

Explain:

i) Sulphur shows variable covalency of +2 and +4 .

(vii) Assertion: An orbital cannot have more than two electrons, moreover, if an orbital has more

than two electrons they must have opposite spin.

Reason: No two electrons in an atom can have all the four quantum numbers the same.

(a) Assertion is false but Reason is true.

(b) Assertion is true but Reason is false.

(c) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

(d) Both Assertion and Reason are true but Reason is not the correct explanation for Assertion.

SECTION B – 20 MARKS

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3

4

Draw the structural formula of a) 3-Chloro phenol b) 2,4,6 trinitro benzaldehyde

OR

Draw the bond line structure of a) 2,3 dimethyl pentene b) Cyclopropanol.

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0.25 g of a dibasic acid were dissolved in water and volume made upto100 ml. 10 ml of this solution required 12.5 ml of N/30 sodium hydroxide solution for complete neutralization. Find the molecular mass of the acid.

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7

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9

10

A spectral line in the Balmer series of hydrogen spectrum corresponds to the wavelength 6561 A. Find the energy levels involved in the transition responsible for the origin of this line. (R=109679cm--1).

11

a. Write the set of four quantum numbers for 26th electron of nickel (Ni=28)

b. Arrange the following orbitals in the increasing order of energy: 6p, 5d, 4f, 7s.

SECTION C – 21 MARKS

12

The atomic numbers of three elements X, Y and Z are: A-2, A and A+1 respectively. B is an inert gas.

State:

i) Predict which elements are having highest and lowest atomic radii.

ii) Which one is most electronegative and which one is most electropositive?

iii) Arrange them according to the increasing order of their Ionisation potential.

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14

15

i) Which element shows diagonal relationship with boron?

ii) Give reason:

a)  Ionisation enthalpy of oxygen is lower than nitrogen, though across period ionisation enthalpy increases.

b) Lower members of p-block elements (e.g. Pb and Sn) show variable valencies.

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Explain:

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i) What is the molality of a solution prepared by dissolving 0.5g of a substance having molecular mass of 74.5 in 100 g of water?

ii) The ratio of masses of oxygen gas and nitrogen gas in a gaseous mixture is 1:4. What is the ratio of the number of their molecules? (O=16, N=14 )

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SECTION D – 15 MARKS

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OR

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i) State an appropriate chemical test used to distinguish between the following pairs of compounds:

(a) Propene and propyne

(b) But – 1 – yne and but – 2 – yne

(c) Ethane and Ethene

ii) How will you convert the following:

(a) Propene to 2 - bromopropane

(b) Ethyl alchohol to ethene

21

i) How will you convert the following? (Give balanced equations)

a) Ethyne to propyne

b) Ethane to butane

c) Benzene to toluene

CHECK: ISC Class 11 Half Yearly Chemistry Sample Paper 2025; Download Free PDF