JEE Main 2023 · 8 April · morning · Single correct · +4 / −1
Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Butan -1- ol has higher boiling point than ethoxyethane.
Reason R: Extensive hydrogen bonding leads to stronger association of molecules.
In the light of the above statements, choose the correct answer from the options given below:
- (a) A is false but R is true
- (b) Both A and R are true but R is not the correct explanation of A
- (c) Both A and R are true and R is the correct explanation of A
- (d) A is true but R is false
Answer and solution
Answer (c) Both A and R are true and R is the correct explanation of A
Solution
Chemistry ma’am · 3 steps
Same formula, same mass: the only difference is the O–H group, and that is what holds butan-1-ol together.
- Fair comparison. Butan-1-ol and ethoxyethane are both C₄H₁₀O with molar mass 74 g mol⁻¹. So any big difference in boiling point must come from the forces between molecules, not from size.
Compound O–H group? Main intermolecular force Boiling point Butan-1-ol, CH₃CH₂CH₂CH₂OH Yes Intermolecular hydrogen bonding about 391 K Ethoxyethane, C₂H₅OC₂H₅ No, H is bonded only to C weak dipole–dipole and dispersion about 308 K - Why R explains A. In the alcohol, the H on one O–H is attracted to the O of the next molecule, so the molecules stay linked together. Boiling has to break these hydrogen bonds, which needs extra energy. The ether has no H on oxygen, so it cannot hydrogen bond with itself, and its molecules separate easily.
- So. A is true, R is true, and the stronger association from hydrogen bonding is exactly why butan-1-ol boils higher. The answer is (c).
The idea to keep. When two compounds have nearly the same mass, check for H bonded directly to N, O or F. The one that can hydrogen bond with itself boils much higher.
Answer from the NTA final answer key. Solution by PrepWiser.