Q. The molal elevation constant for water is 0.52. What will be the boiling point of 2 molar sucrose solution at 1 atm pressure? (Assume b.p. of pure water is $100℃$)
A) $101.04℃$
B) $100.26℃$
C) $100.52℃$
D) $99.74℃$
Explanation
(a)
$\mathrm{\Delta}T_{b} = k_{b} \times molality$
for dilute solution
molarity=molality=2(given)
and $\ \ k_{b} = 0.52(given)\ \$
$\ \therefore$ $\ \ \mathrm{\Delta}T_{b} = 0.52 \times 2 = 1.04℃$
Now ,
$\mathrm{\Delta}T_{b} =$ boiling point of solution – boiling point of solvent
(i.e., $H_{2}O$)
$\therefore$ boiling point of solution =$\mathrm{\Delta}T_{b} + b.pt\ of\ H_{2}O$
=1.04+100 =101.04$℃$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.