1.

Calculate the molecular weight of a substance whose `7.0%` (by weight) solution in water freezes at `-0.89^(@)C`. `(k_(f) "for" H_(2)O=1.86K"molality"^(-1)`).

Answer» `DeltaT_(f)=K_(f)xx"Molality"=K_(f)xx(wxx1000)/(mxxW)`
w=7 g, W=100-7=93g, `DeltaT_(f)=0.89, K_(f)=1.86`
`:.` Molecular wt.,
`m=(K_(f)xxwxx1000)/(WxxDeltaT_(f))=(1.86xx7xx1000)/(93xx0.89)`
`=157.30`


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