🛠️ JEE🧪 Chemistry

Chemical Bonding and Molecular Structure

4 solved JEE Chemistry previous year questions on Chemical Bonding and Molecular Structure, each with the correct answer and a full explanation.

Hydrogen bonding plays a central role in which of the following phenomena?

aIce floats in water

bHigher Lewis basicity of primary amines than tertiary amines in aqueous solutions

cFormic acid is more acidic than acetic acid

dDimerisation of acetic acid in benzene

✓ Correct answer: a) Ice floats in water

ExplanationA — Ice floats in water Ice has an open hexagonal structure due to extensive hydrogen bonding, making it less dense than liquid water. ✔ Hydrogen bonding involved B — Higher Lewis basicity of primary amines than tertiary amines in aqueous solution Primary amines form stronger hydrogen bonds with water, making them more solvated and thus effectively more basic in water. ✔ Hydrogen bonding involved C — Formic acid stronger than acetic acid | | JEE This is due to +I effect of –CH₃ reducing acidity in acetic acid, not due to hydrogen bonding. ❌ Not due to hydrogen bonding D — Dimerisation of acetic acid in benzene Acetic acid forms cyclic dimers via intermolecular hydrogen bonding in non- polar solvents like benzene. ✔ Hydrogen bonding involved Final Answer: A, B and D

When the hybridization state of carbon atom changes from sp3 to sp2 and finally to sp, the angle between the hybridized orbitals:

adecreases gradually.

bdecreases considerably.

cis not affected.

dincreases progressively.

✓ Correct answer: d) increases progressively.

ExplanationWhen the hybridization state of carbon atom changes from sp3 to sp2 and finally to sp, the angle between the hybridized orbitals increases progressively.

The species having pyramidal shape is

a(a)

b(b)

c(c)

d(d)

✓ Correct answer: d) (d)

ExplanationStep 1: Analyze each molecule (A) SO₃ Central atom: S Bonds: 3 S=O double bonds Lone pairs on S: 0 Electron geometry: trigonal planar → Molecular shape: trigonal planar, not pyramidal ❌ (B) BrF₃ Central atom: Br Bonds: 3 Br–F Lone pairs: 2 on Br Electron geometry: trigonal bipyramidal Molecular shape: T-shaped (not pyramidal) ❌ (C) SiO₃²⁻ Central atom: Si Bonds: 3 Si–O Lone pairs: 0 Molecular shape: trigonal planar ❌ (D) OSF₂ Central atom: S Bonds: S=O and 2 S–F Lone pairs on S: 1 Electron geometry: tetrahedral Molecular shape: pyramidal ✅ ✅ Step 2: Conclusion Pyramidal species: OSF₂ Answer: D — OSF₂

Which one of the following statements about water is FALSE?

aWater can act both as an acid and as a base.

bThere is extensive intramolecular hydrogen bonding in the condensed phase.

cIce formed by heavy water sinks in normal water.

dWater is oxidized to oxygen during photosynthesis.

✓ Correct answer: b) There is extensive intramolecular hydrogen bonding in the condensed phase.

Explanation(B) In condensed phase water has inter molecular hydrogen bonding. [New NCERT Class 11th Page No. 101]

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