Boiling point of water at 750 mm Hg is 99.63°C. How much sucrose is to be added to

Boiling point of water at 750 mm Hg is 99.63°C. How much sucrose is to be added to 500 g of water such that it boils at 100°C. Molal elevation constant for water is 0.52 K kg mol⁻¹.

Solution

Normal boiling point of water = 100 C

Elevation of boiling point, ∆Tb = 100 − 99.63  = 0.37

Mass of water w₁= 500 g

Molar mass of sucrose (C₁₂H₂₂O₁₁),M₂= 11 × 12 + 22 × 1 + 11 × 16 = 342 g mol⁻¹

Molal elevation constant, K_b = 0.52 K kg mol−1

Use the formula 

w₂= 121.67 g

Answer   mass of added sucrose = 121.67 g