Boiling Point Elevation Overview
When a non-volatile solute is added to a solvent, the boiling point of the resulting solution increases. This phenomenon is known as boiling point elevation. The extent of this increase depends on the number of solute particles in the solution.
Calculation of Boiling Point Elevation
- The formula for boiling point elevation is given by:
ΔT_b = i * K_b * m
Where:
- ΔT_b = change in boiling point
- i = van 't Hoff factor (number of particles the solute breaks into)
- K_b = ebullioscopic constant of the solvent
- m = molality of the solution
Understanding Sucrose and NaCl
- Sucrose:
- Sucrose is a non-electrolyte that does not dissociate in solution, so the van 't Hoff factor (i) is 1.
- Given that the boiling point elevation for a sucrose solution is 1.0°C, it can be concluded that:
ΔT_b for sucrose = 1.0°C
- NaCl:
- Sodium chloride (NaCl) is an electrolyte that dissociates into two ions: Na⁺ and Cl⁻. Thus, i for NaCl is 2.
- For the same molal concentration, the boiling point elevation for NaCl can be calculated as follows:
ΔT_b for NaCl = i * ΔT_b for sucrose = 2 * 1.0°C = 2.0°C
Conclusion
- Therefore, the boiling point of the NaCl solution will increase by 2.0°C compared to the pure solvent. If the boiling point of pure water is 100°C, the boiling point of the NaCl solution will be:
Boiling Point of NaCl Solution = 100°C + 2.0°C = 102.0°C

102 degree Celsius