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Two aqueous solution containing, respect...

Two aqueous solution containing, respectively, 7 g urea (molar mass = 60 g) and 42 g of substance `X` in `100 g` of water freeze at the same temperarture. Calculate the molecular weight of `X`.

Text Solution

Verified by Experts

The given values are:
`W_("urea")=7 g`
`W_(X) = 42 g`
`W_(A)=100 g`
Now using formula, `Mw_(B)=(K_(f)xxW_(B)xx1000)/(DeltaT_(f)xxW_(A))`
For urea, `Mw_(B)=(K_(f)xx7xx1000)/(DeltaT_(f)xx1000)` ….(i)
For `X Mw_(B)=(K_(f)xx42xx1000)/(DeltaT_(f)xx1000)` ….(ii)
Dividing Eq.(i) from (ii), we get
`(60/Mw'_(B))=7/42` or`Mw'_(B)=360`
`:.` Molecular weight of `X = 360 g mol^(-1)`
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