Molecules of benzoic acid () dimerise in 30 g of benzene. 'w' g of benzoic acid shows a depression in freezing point equal to 2 K. If the percentage association of the acid to form dimer in the soluti

Question

Molecules of benzoic acid () dimerise in 30 g of benzene. 'w' g of benzoic acid shows a depression in freezing point equal to 2 K. If the percentage association of the acid to form dimer in the solution is 80, then w is:

(Given that , molar mass of benzoic acid = 122 g mol⁻¹)

Canvas Classes · Accepted Answer

Strategy:
 Benzoic acid undergoes association (dimerization) in benzene. First, find the van't Hoff factor for the given percentage association, then use the depression formula to solve for the required mass .

Step 1: Calculate the van't Hoff factor ()
For dimerization () with :

Step 2: Calculate the required molality ()
, .

Step 3: Solve for mass } w 	ext{
Solvent mass = 30 g = 0.03 kg.

Mass of acid () = moles  molar mass = .
Rounding to nearest tenth: 2.4.

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