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1.02 g of urea when dissolved in 98.5 g ...

1.02 g of urea when dissolved in 98.5 g of certain solvent decreases its freezing point by 0.211K. 1. 609 g of unknown compound when dissolved in 86 g of the same solvent depresses the freezing point by 0.34 K. Calculate the molar mass of the unknown compound.
(Molar mass of urea= 60 g `mol^(-1)`

Text Solution

Verified by Experts


`1000K_f`=`(M_2 xxDeltaT_f xx W_1)/(W_2)`
`1000K_f`= `(M_2 xx DeltaT._f xx W._1)`
= `(60 g mol^(-1)xx 0.211 K xx 98.5 g)/(1.02g)`
=`(M_2xx0.34K xx 86 g)/(1.609 g)`
`(1247.01 g K mol(-1))/(1.02)` = `(M._2xx 29.24 K)/(1.609)`
`1222.55 g K mol^(-1)`=`M_2 xx 18.173`
`M_2=(1222.55 g K mol^(-1))/(18.175 K)` = 67.3 g `mol^(-1)`
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