Question

Which of the following can show positive deviation from Raoult's law?

• A. Water-hydrochloric acid
• B. Water-nitric acid
• C. Benzene-methanol
• D. Acetone-chloroform

Answer 1

Answer: (B)

Water-nitric acid

Answer 2

In solution showing positive type of deviation the partial pressure of solution is greater than the vapour pressure as expected according to Raoult's law. In solution of methanol & benzene methanol molecules are held together due to hydrogen bonding as shown below. On adding benzene, the benzene molecules get in between the molecule of methanol thus breaking the hydrogen bonds. As the resulting solution has weak intermolecular attraction, the escaping tendency of alcohol and benzene molecule from the solution increases. Consequently the vapour pressure of the solution is greater than the vapour pressure as expected from Raoult's law.