Which of the following liquid pairs shows a positive deviation from Raoult’s law?
- AWater – hydrochloric acid
- BAcetone – chloroform
- CWater – nitric acid
- DBenzene – methanol
Solution & Step-by-step Explanation
Positive deviation occurs when the interactions between the different components (A-B) are weaker than those between like components (A-A or B-B).
In the case of benzene and methanol, methanol molecules are hydrogen-bonded. When benzene is added, it breaks some of these hydrogen bonds, making it easier for molecules to escape into the vapor phase, thereby increasing the vapor pressure above the expected Raoult's value.
The other pairs listed show negative deviation due to stronger interactions (like hydrogen bonding between acetone and chloroform).
In the case of benzene and methanol, methanol molecules are hydrogen-bonded. When benzene is added, it breaks some of these hydrogen bonds, making it easier for molecules to escape into the vapor phase, thereby increasing the vapor pressure above the expected Raoult's value.
The other pairs listed show negative deviation due to stronger interactions (like hydrogen bonding between acetone and chloroform).