Chemistry · 2019
JEE Main · 12 January 2019, Shift 2 · Q56
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…
Molecules of benzoic acid $\displaystyle \left(\mathrm{C}_6 \mathrm{H}_5 \mathrm{COOH}\right)$ dimerise in benzene. 'w' g of the acid dissolved in $\displaystyle 30$ g of benzene shows a depression in freezing point equal to $\displaystyle 2$ K. If the percentage association of the acid to form dimer in the solution is $\displaystyle 80$, then w is : (Given that $\displaystyle \mathrm{K}_{\mathrm{f}}=5 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$, Molar mass of benzoic acid $\displaystyle =122 \mathrm{~g} \mathrm{~mol}^{-1}$ )
Official answer
(3)
$\displaystyle 2.4 \mathrm{~g}$
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