Question

Which of the following shows a negative deviation from Raoult's law?

• A. ${\mathrm{C}}_6{\mathrm{H}}_6\mathrm{and}{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$
• B. ${\mathrm{C}}_6{\mathrm{H}}_6\mathrm{and}{\mathrm{CCl}}_4$
• C. ${\mathrm{CHCl}}_3$ and Acetone
• D. ${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{CH}}_3\mathrm{and}{\mathrm{C}}_6{\mathrm{H}}_6$

Answer 1

The correct option is C

${\mathrm{CHCl}}_3$ and Acetone

Explanation for correct option:

C. ${\mathrm{CHCl}}_3$ and Acetone

Roult's law:

• “Raoult’s law states that for a solution of volatile liquids, the partial vapor pressure of each component of the solution is directly proportional to its mole fraction present in solution.”
• It can be expressed as:
• $p=p^{0}x$, where $p$ is the vapor pressure of the component of the solution, ${\mathit{p}}^{\mathit{0}}$ is the vapor pressure of the pure component and $x$ is the mole fraction.
• “When a solution does not obey Raoult’s law over the entire range of concentration, then it is called a non-ideal solution.”
• The vapor pressure of such a solution is either higher or lower than that predicted by Raoult’s law.
• “If it is higher, the solution exhibits positive deviation and if it is lower, it exhibits negative deviation from Raoult’s law.”

${\mathrm{CHCl}}_3$ and Acetone:

• “A mixture of chloroform and acetone forms a solution with negative deviation from Raoult’s law. This is because chloroform molecule is able to form a hydrogen bond with acetone molecule.”

Explanation for incorrect options:

All other mixtures do not show negative deviation due to the absence of hydrogen bonding or strong interactions. Thus, options A, C, and D are incorrect.

Hence, the correct option is C i.e. ${\mathrm{CHCl}}_3$ and Acetone.