Chemistry class 12th Elevation of boiling point

Elevation of Boiling Point


1. Introduction

Elevation of boiling point is one of the colligative properties of solutions. It states that when a
non-volatile solute is added to a solvent, the boiling point of the solution increases. This happens
because the addition of solute particles lowers the vapor pressure of the solvent, requiring a higher
temperature to reach the boiling point.


2. Definition and Explanation

Boiling point is the temperature at which the vapor pressure of a liquid becomes equal to the
external pressure. When a solute is added, the vapor pressure decreases, so the solution must be
heated to a higher temperature to reach the same external pressure.


The increase in boiling point due to the presence of a solute is called the **Elevation of Boiling
Point** and is denoted as **Delta Tb**.


3. Formula and Derivation

The elevation in boiling point is given by the formula:


Delta Tb = Kb * m


where:
- Delta Tb = Elevation in boiling point (Tb - Tb^0)
- Kb = Molal boiling point elevation constant
- m = Molality of the solution


Since molality (m) is defined as:
m = (n2 / w1) * 1000


where:
- n2 = Moles of solute