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 )

Question

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 ) (A) 1.8 g (B) 2.4 g (C) 1.0 g (D) 1.5 g

Tardigrade Admin · Accepted Answer

2 undersetWg( C 6 H 5 COOH ) xrightarrow C 6 H 6 underset textdiner( C 6 H 5 COOH )2 Δ1 T=i kr m 2=0.6 × 5 × (w × 1000/122 × 30) (i=1-0.8+0.4=0.6) w=2.44 g

1.8 g

2.4 g

1.0 g

1.5 g

2Wg(C6​H5​COOH)​C6​H6​​diner(C6​H5​COOH)2​​ Δ1​T=ikr​m 2=0.6×5×122×30w×1000​ (i=1−0.8+0.4=0.6) w=2.44g

$2 W g (C_{6} H_{5} COO H) C_{6} H_{6} diner (C_{6} H_{5} COO H)_{2}$
$Δ_{1} T = i k_{r} m$
$2 = 0.6 \times 5 \times \frac{w \times 1000}{122 \times 30}$
$(i = 1 - 0.8 + 0.4 = 0.6)$
$w = 2.44 g$