Associate Safety Professional Practice Exam

Which of the following: benzene, toluene, xylene or acetone has the highest vapor pressure?

1. Benzene

2. Toluene

3. Xylene

4. Acetone

The correct answer is: Acetone

Acetone has the highest vapor pressure among the options listed. Vapor pressure is influenced by the molecular weight and intermolecular forces present in a substance. Acetone is a small, low molecular weight molecule that has weaker intermolecular forces compared to the other substances mentioned. Benzene, while it is also a relatively low molecular weight molecule, has stronger π-π interactions due to its aromatic nature. Toluene and xylene, being derivatives of benzene with additional methyl groups, have even higher molecular weights and stronger intermolecular forces, which contribute further to lower vapor pressures. The strong molecular interactions in benzene, toluene, and xylene result in lower vapor pressures compared to acetone’s comparatively weak interactions, allowing acetone to evaporate more readily at room temperature, thereby exhibiting a higher vapor pressure.