Solutions and Colligative Properties - Result Question 29-1
29. $1.22 \mathrm{~g}$ $ \mathrm{C}_6 \mathrm{H}_5 \mathrm{COOH}$ is added into two solvents and data of $\Delta T_b$ and $K_b$ are given as :
(i) In $100 \mathrm{~g} $ $\mathrm{CH}_3 \mathrm{COCH}_3 $ $\Delta T_b=0.17, K_b=1.7 \mathrm{~K} \mathrm{~kg} / \mathrm{mol}$
(ii) In $100$ g benzene, $\Delta T_b=0.13$ and $K_b=2.6 \mathrm{~K} \mathrm{~kg} / \mathrm{mol}$
Find out the molecular weight of $\mathrm{C}_6 \mathrm{H}_5 \mathrm{COOH}$ in both the cases and interpret the result.
(2004, 2M)
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Solution:
(i) $\Delta T_b=K_b \cdot m_2$
$ \Rightarrow 0.17=1.7 \times \dfrac{1.22}{M} \times \dfrac{1000}{100} \Rightarrow M=122 $
(ii) $0.13=2.6 \times \dfrac{1.22}{M} \times \dfrac{1000}{100} \Rightarrow M=244$
The above molar masses suggests thapt benzoic acid is monomeric in acetone while dimeric in benzene.
BETA
