Benzoic acid molecules undergo dimerisation i | vedclass

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Question

(A) $1$. Calculate the observed molality $(m_{obs})$: $\Delta T_f = K_f 	imes m_{obs} \implies 2 = 5 	imes m_{obs} \implies m_{obs} = 0.4 \ mol \ kg

Vedclass · Accepted Answer

$80$

Vedclass · Answer

(A) $1$. Calculate the observed molality $(m_{obs})$: $\Delta T_f = K_f 	imes m_{obs} \implies 2 = 5 	imes m_{obs} \implies m_{obs} = 0.4 \ mol \ kg^{-1}$.$2$. Calculate the theoretical molality $(m_{theo})$: Moles of benzoic acid $= \frac{2.44 \ g}{122 \ g \ mol^{-1}} = 0.02 \ mol$. Mass of solvent $= 0.03 \ kg$. $m_{theo} = \frac{0.02}{0.03} = 0.667 \ mol \ kg^{-1}$.$3$. Calculate the van't Hoff factor $(i)$: $i = \frac{m_{obs}}{m_{theo}} = \frac{0.4}{0.667} = 0.6$.$4$. For dimerisation,$i = 1 - \alpha + \frac{\alpha}{2} = 1 - \frac{\alpha}{2}$.$5$. $0.6 = 1 - \frac{\alpha}{2} \implies \frac{\alpha}{2} = 0.4 \implies \alpha = 0.8$.$6$. Percentage of association $= 0.8 	imes 100 = 80\%$.

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