Question

Van’t Hoff factor, when benzoic acid is dissolved in benzene, will be:
(A)2
(B)1
(C)0.5
(D)1.5

Answer 1

Van’t Hoff factor of the molecules can be calculated by using the following formula,
$\text{Van }\\!\\!'\\!\\!\text{ t Hoff factor i=}\dfrac{\text{n (Observed)}}{\text{n (Theoretical) }}$
n (observed) = number solute particles present in the solution
n (Theoretical) = number of solute particles without considering association and dissociation.

Complete step by step answer:

The structure of benzoic acid is as follows.

The benzoic acid is soluble in water and benzene also.
The molecular weight of benzoic acid is 122, but the observed molecular weight is 242.
The observed molecular weight is double the expected molecular weight.
This indicates that an association of benzoic acid in benzene solution into dimers.
Therefore the Van’t Hoff factor of benzoic acid in benzene is

& \text{Van }\\!\\!'\\!\\!\text{ t Hoff factor i=}\dfrac{\text{n (Observed)}}{\text{n (Theoretical) }} \\\ & \text{ = }\dfrac{1}{2}=0.5 \\\ \end{aligned}$$ >The Van’t Hoff factor for benzoic acid in benzene is 0.5. **So, the correct option is C.** **Additional information:** >Benzoic acid is most regularly found in industries to manufacture a wide variety of products like perfumes, dyes, and as an insect repellent. >Benzoic acid is available naturally in many plants and is involved in the biosynthesis of several secondary metabolites. **Note:** Benzoic acid in the solution form dimers due to the presence of hydrogen bonding. Hydrogen bonding makes two molecules of benzoic acid into a single molecule by holding the two molecules together. The process of formation of a dimer is called dimerization. By using the Van't Hoff factor we can find the numbers of molecules present in the solution