Chemistry Gases NUMS 2022
PMDC Verified Question 47 of 65
Which of the following molecules will show a higher rate of evaporation?
A
Acetone
B
Water
C
Ethanol
D
Ethylene glycol
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Acetone
Concept:

The rate of evaporation of a liquid is inversely proportional to the strength of its intermolecular forces (IMF). Liquids with weaker IMFs have lower boiling points and evaporate much faster.

Solution:

  • Let's analyze the intermolecular forces in the options. Water, Ethanol, and Ethylene Glycol all possess extremely strong hydrogen bonding.


  • Ethylene glycol has two -OH groups, creating massive hydrogen bonding networks (highest boiling point).


  • Water has a highly efficient hydrogen bonding network (boiling point 100°C).


  • Ethanol has one -OH group, resulting in moderate hydrogen bonding (boiling point 78°C).


  • Acetone (propanone) is a ketone with polar carbonyl bonds, meaning it only has dipole-dipole interactions. Because dipole-dipole forces are much weaker than hydrogen bonding, acetone breaks surface tension easily and evaporates very rapidly (boiling point ~56°C).


Why other options are incorrect:

  • Options B, C, & D: These all contain hydrogen bonds, making their molecules cling tightly together, significantly slowing down the rate of evaporation compared to acetone.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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