Properties such as boiling point, freezing point and vapour pressure of a pure solvent change when solute molecules are added to get homogenous solution. These are called colligative properties. Application of colligative properties are very useful in day-to-day life. One of its example is the use of ethylene glycol and water mixture as anti-freezing liquid in the radiator of automobiles.
A solution M is prepared by mixing ethanol and water. The mole fraction of ethanol in the mixture is `0.9`.
Given : Freezing point depression constant of water `(K_(f)^("water")) = 1.86 K "mol"^(-1)`
Freezing point depression constant of ethanol `(K_(f)^("ethonal")) = 2.0 K kg "mol"^(-1)`
Boiling point elevation constant of water `(K_(b)^("water")) = 0.52 K kg "mol"^(-1)`
Boiling point elevation constant of ethanol `(K_(b)^("ethonal")) = 1.2 K kg mol^(-1)`
Standard freezing point of water `= 273 K`
Standard freezing point of ethonal `= 155.7 K`
Standard boiling point of water `= 373 K`
Standard boiling point of ethanol `= 351.5 K`
Vapour pressure of pure water `= 32.8 mm Hg`
Vapour pressure of pure ethonal `= 40 mm Hg`
Molecular weight of water `= 18 g "mol"^(-1)`
Molecular weight of ethonal `= 45 g"mol"^(-1)`
In answering the following questions, consider the solution to be ideal ideal solutions and solutes to be non-volatile and non-dissociative.
Water is added to the solution M such lthat the molecules fraction of water in t he solution becomes `0.9`. The boiling point of this solution is :

Options

A. 380.4 K
B. 376.2 K
C. 375.5 K
D. 354.7 K

Explanation

Molality of new solutioni `=0.1/(0.9xx18)xx1000=6.17`
`DeltaT_(b)=K_(b)m=0.52xx6.17=3.2`
Final B.P. of solution `=373+3.2=376.2K`