1. Tardigrade
  2. Question
  3. Chemistry
  4. Molecules of benzoic acid ( C 6 H 5 COOH ) dimerise in benzene. ' 'w'g of the acid dissolved in 30 g of benzene 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 Kf=5 K kg mol -1, Molar mass of benzoic acid =122 g mol -1 )

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Q. Molecules of benzoic acid $\left( C _{6} H _{5} COOH \right)$ dimerise in benzene. ' $'w'g$ of the acid dissolved in $30 g$ of benzene 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 $K_{f}=5 \,K \,kg \,mol ^{-1}$, Molar mass of benzoic acid $=122\, g\,mol ^{-1}$ )

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Solution:

$2\underset{Wg}{\left( C _{6} H _{5} COOH \right)} \xrightarrow{ C _6 H _6}\underset{\text{diner}}{\left( C _{6} H _{5} COOH \right)_2}$
$\Delta_{1} T=i k_{r} m$
$2=0.6 \times 5 \times \frac{w \times 1000}{122 \times 30}$
$(i=1-0.8+0.4=0.6)$
$w=2.44 \,g$