The difference between the boiling point and freezing point of an aqueous solution containing sucrose (molecular mass `= 342 g mol^(-1))` in 100 g of water is `105.04`. If `K_(f)` and `K_(b)` of water are 1.86 and `0.51 Kg mol^(-1)` respectively, the weight of sucrose in the solution is about

Options

A. 34.2 g
B. 342 g
C. 7.2 g
D. 72 g

Answer

D

Explanation

`"Given,"T_(b)-T_(f)=105.0^(@)C`
`rArr(100+DeltaT_(b))-(0-DeltaT_(f))=105^(@)C`
`DeltaT_(b)+DeltaT_(f)=5`
`DeltaT_(b)+DeltaT_(f)=(K_(b)+K_(f))xxm" "("m=molality")`
`rArr5=(1.86+0.51)xx(wxx1000)/(342xx100)`
`:.w=(1710)/(23.7)=72.15g~=72g`