Question

Explain the following:

An aqueous solution of urea boils above 100°C but freezes below 0°C.

Answer 1

Urea is a non-volatile solute. When dissolved in water, it lowers the vapour pressure, causing the solution to boil above 100°C (boiling point elevation) and freeze below 0°C (freezing point depression). These are colligative properties, depending only on the number of solute particles.