1.

How much ethly alcohol much be added ot 1.0 litre of water so that the solution may treeze at `-10^(@)C. (K_(f) "for water =1.88 K kg" mol^(-1), "density of water=1 g "mL^(-1)).`

Answer» Correct Answer - 247.3g
Step I. Calculation of molality of the solution.
`DeltaT_(f)=K_(f)xxm`
`DeltaT_(f)=0^(@)C-(-10^(@)C)=10^(@)C=10 K, K_(f)=1.86" K kg mol"^(-1)`
`m=(DeltaT_(f))/K_(f)=((10K))/((1.86" K kg mol"^(-1)))=5.376" mol kg"^(-1)=5.376 m.`
Step II. Calculation of amount of ethyl alcohol to be added.
`"Molality (m)"=("Mass of ethyl alcohol / Molar mass")/("Mass of water / 1000")`
`5.376" mol kg"^(-1)=(W_(B)//(46"g mol"^(-1)))/(1" kg")`
`W_(B)=(5.376" mol kg"^(-1))xx(46" g mol"^(-1))xx(1 kg)=247.3 g.`


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