Boiling Point Elevation Calculator
Calculate boiling point elevation using ΔTb = i × Kb × m. Supports water, benzene, ethanol, and acetone. Includes altitude correction and van't Hoff factor for ionic solutes.
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ΔTb (Boiling Point Elevation)
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New Boiling Point —
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mol/kg
°C·kg/mol
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ΔTb
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New Boiling Point —
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ΔTb (Elevation)
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Molality —
Altitude BP Correction —
Corrected Base BP —
Final Boiling Point —
How to Use This Calculator
- Enter the molality of your solution (mol solute per kg solvent).
- Select or enter the ebullioscopic constant Kb for your solvent.
- Enter the van't Hoff factor i (1 for non-electrolytes, ~1.85 for NaCl).
- Optionally enter altitude to correct the base boiling point.
Formula
ΔTb = i × Kb × m
New Boiling Point = BP₀ + ΔTb − (altitude correction)
Altitude correction ≈ −0.34 °C per 100 m elevation
Example
Example: 1 mol NaCl (i = 1.85) in 1 kg water (Kb = 0.512): ΔTb = 1.85 × 0.512 × 1 = 0.947 °C. New boiling point = 100 + 0.947 = 100.95 °C.
Frequently Asked Questions
- Boiling point elevation is a colligative property: dissolving a solute in a solvent raises the boiling point. The elevation ΔTb = i × Kb × m, where i is the van't Hoff factor, Kb is the ebullioscopic constant, and m is molality.
- Adding salt slightly raises the boiling point (e.g., 1 tsp salt in 1 L raises BP by only ~0.02 °C). This negligible change does not meaningfully speed up boiling — the main culprit for perception is that salted water actually reaches boiling at a marginally higher temperature.
- Water's Kb is 0.512 °C·kg/mol. A 1 molal solution of a non-dissociating solute boils at 100.512 °C at sea level.
- At higher altitudes, lower atmospheric pressure reduces the boiling point by approximately 0.34 °C per 100 m. At 3,000 m (Denver area), water boils around ~90 °C.
- Both arise from Raoult's Law: solute particles reduce solvent vapor pressure. The solvent must be heated to a higher temperature to overcome the reduced vapor pressure and reach atmospheric pressure.
Related Calculators
Sources & References (5) ▾
- Colligative Properties — ACS Chemistry for Life — American Chemical Society
- OpenStax Chemistry 2e, Chapter 11: Colligative Properties — OpenStax
- IUPAC Compendium of Chemical Terminology — Ebullioscopic Constant — IUPAC
- NIST Chemistry WebBook — Fluid Properties — NIST
- Atkins' Physical Chemistry, 11th Ed. — Chapter 5: Simple Mixtures — Oxford University Press