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Benzoic acid of mass 3.9 g is dissolved ...

Benzoic acid of mass 3.9 g is dissolved in 49g of benzene which shows a depression in freezing point of 1.62 K. Predict whether benzoic acid is associated or dissociated. `("Given, molar mass of benzoic acid = 122 g mol"^(-1) and K_f= "4.9K kg mol"^(-1))`

Text Solution

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The given quantities are
`W_(2)=3.9g, W_(1)=4.9g`
`triangleT_(f)=1.62K`,
`K_(f)=4.9" K kg mol"^(-1)`
Apply van.t Hoff equation `triangleT_(f)=I K_(f) xx m`
here i=Number of ions
`triangleT_(f)=(i. K_(f) xx W_(2) xx 1000)/(M_2 xx W_(1)) {therefore m=(W_(2) xx 1000)/(M_(1) xx W_(1))}`
`rArr 1.62K =(i.49" K kg mol"^(-1) xx 3.9 xx 1000)/(122" g mol"^(-1) xx 49g)`
As the value of `i lt 1`, thus beozoic acid is an associated solute.
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