Question

If equimolar solutions of urea, NaCl, sucrose and BaCl₂ have boiling points A, B, C, and D then, 
a) A = C < B < D

b) A = D < B < D

c) A > B > C < D

d) A < B < C < D​

Answer 1

Given info : if equimolar solutions of urea , NaCl , sucrose and BaCl₂ having boiling point A , B , C and D respecitvely.

To find : the relation between the boiling points is ...

solution : we know, $\Delta T_b=iKm$

we see boiling point depends on the value of Van't Hoff's factor and molality of the solution.

for urea and sucrose,

 Van't Hoff's factor is not considered as it is covalent compound. and also it has given that the solutions are equimolar, so the no of moles of solute in a solution must be same hence, for specific amount of solvent , molality must be same.

There boiling points for urea and sucrose are same if both are in same solvent. i.e., A = C

for NaCl,  [ NaCl ⇄ Na⁺ + Cl⁻ ]

Van't Hoff's factor , i = 1 - α + α + α = 1 + α = 1 + 1 = 2 [ assuming 100% dissociation]

similarly , for BaCl₂  [BaCl₂ ⇄ Ba²⁺ + 2Cl⁻ ]

Van't Hoff factor, i = 1 - α + α + 2α = 1 + 2α = 1 + 2 = 3

here you see, Van't Hoff's factor of NaCl is less than that of BaCl₂.

so the boiling points relation would be , B < D

therefore the order of the boiling points is A = C < B < D