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A solution of 0.643 g of an organic comp...

A solution of `0.643 g` of an organic compound in `50 mL` of benzene (density `0.879 g//mL`) lowered its freezing point from `5.51^(@)C` to `5.03^(@)C`. Calculate the molecular weight of solid. `(K_(f)` for benzene is `5.12 K mol^(-1) kg`)

Text Solution

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Given `W = "wt. of benzene" = V xx d = 50 xx 0.879 g`,
`Delta T = 5.51 - 5.03 = 0.48, w = 0.643 g`,
`K'_(f) = 5.12 K mol^(-1) kg`
`Delta T = (1000 xx K'_(f) xxw)/(m xx W)`
`:. 0.48 = (1000 xx 5.12 xx 0.643)/(m xx 50 xx 0.879)`
`:. m = 156.06`
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