At 100∘C, pure water boils, so its vapour pressure (p∘) is equal to the atmospheric pressure, which is 760 mm Hg.
Given vapour pressure of the solution (ps) = 732 mm Hg.
Mass of solvent water (w1) = 100 g=0.1 kg.
Molar mass of water (M1) = 18 g mol−1.
According to the relative lowering of vapour pressure:
psp∘−ps=n1n2
732760−732=100/18n2
73228=5.555n2
n2=73228×5.555≈0.2125 mol
Now, calculate the molality (m) of the solution:
m=w1 (in kg)n2=0.10.2125=2.125 mol kg−1
Elevation in boiling point (ΔTb) is given by:
ΔTb=Kb×m=0.52×2.125≈1.105∘C
Therefore, the boiling point of the solution is:
Tb=100∘C+1.105∘C=101.105∘C≈101∘C.