Boiling Point Elevation Calculator
Compute boiling point elevation using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
Reviewed by Manoj Kumar, Mathematics Educator
Formula
delta_Tb = i * Kb * m
Where delta_Tb is the boiling point elevation in degrees Celsius, i is the van Hoff factor (number of particles the solute dissociates into), Kb is the ebullioscopic constant of the solvent (C/m), and m is the molality (moles of solute per kilogram of solvent).
Worked Examples
Example 1: Salt in Water
Problem:Calculate the boiling point elevation when 58.44g of NaCl (i=2) is dissolved in 1 kg of water (Kb = 0.512 C/m).
Solution:Molar mass of NaCl = 58.44 g/mol\nMoles of NaCl = 58.44 / 58.44 = 1.0 mol\nMolality = 1.0 mol / 1 kg = 1.0 m\ndelta_Tb = i * Kb * m = 2 * 0.512 * 1.0 = 1.024 C\nNew boiling point = 100 + 1.024 = 101.024 C
Result:Boiling point elevation: 1.024 C | New BP: 101.024 C (213.84 F)
Example 2: Sugar in Water
Problem:Calculate boiling point elevation for 342.3g of sucrose (i=1) in 1 kg of water.
Solution:Molar mass of sucrose = 342.3 g/mol\nMoles = 342.3 / 342.3 = 1.0 mol\nMolality = 1.0 m\ndelta_Tb = 1 * 0.512 * 1.0 = 0.512 C\nNew boiling point = 100.512 C
Result:Boiling point elevation: 0.512 C | New BP: 100.512 C (212.92 F)
Frequently Asked Questions
What is boiling point elevation?
Boiling point elevation is a colligative property where adding a non-volatile solute to a solvent raises its boiling point. When solute particles dissolve in a solvent, they lower the vapor pressure of the solution compared to the pure solvent. Since a liquid boils when its vapor pressure equals the external atmospheric pressure, a solution with lower vapor pressure needs a higher temperature to reach that threshold. The magnitude of the elevation depends only on the number of dissolved particles, not their chemical identity. For water, the ebullioscopic constant is 0.512 degrees Celsius per molal, meaning one mole of non-electrolyte solute per kilogram of water raises the boiling point by about half a degree.
Can boiling point elevation be used to determine molar mass?
Yes, boiling point elevation is a classic laboratory technique for determining the molar mass of an unknown solute, known as ebullioscopy. By dissolving a known mass of the unknown solute in a known mass of solvent and measuring the boiling point elevation, you can calculate the molality and then the molar mass. The formula rearranges to M = (i * Kb * mass_solute) / (delta_T * mass_solvent). This method works best for non-volatile, non-electrolyte solutes dissolved in solvents with large Kb values. Camphor with a Kb of 5.95 is often used in teaching laboratories because it provides large, easily measured temperature changes even with small amounts of solute.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy