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Depression in Freezing Point

Find the degr...

Question

Find the degree of association when $1.0$ gram benzoic acid, dissolved in $25$ gram benzene is having depression in freezing point $0.81 k$ . The molal depression constant for solvent is $4.9 K$ kg ${m o l e}^{- 1}$

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Solution

molar mass of benzoic acid,
$= \frac{1000 \times K_{f} \times m a s s o f b e n z o i c a c i d}{Δ T_{f} \times m a s s o f s o l v e n t}$
$= \frac{1000 \times 4.9 \times 1}{0.81 \times 25}$
$242 g r a m m o l e^{- 1}$
=abnormal (experimental) molar mass of benzoic acid.
van't Hoff factor (i) = $\frac{T h e o r e t i c a l m o l a r m a s s o f b e n z i o c a c i s}{E x p e r i m e n t a l m o l a r m a s s o f b e n z i o c a c i d}$
= $\frac{122}{242} ≅ 0.5$

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