🔍 /

Boiling Point Elevation Calculator

Calculate boiling point elevation for solutions using colligative properties. Find ΔTb from solute mass, molar mass, and solvent Kb constant.

User Rating 0.0 ★★★★★
Total Usage 0 times
Category Physics & Science
Select solvent or enter custom values
Kb: 0.512 °C·kg/mol BP: 100.0 °C
g
Mass of dissolved substance
g/mol
Molecular weight of solute
g
Mass of pure solvent
particles
1 for non-electrolytes, 2 for NaCl, etc.
Examples:

Enter values and click Calculate

Is this tool helpful?

Your feedback helps us improve.

★ ★ ★ ★ ★

About

When a non-volatile solute dissolves in a solvent, the solution's boiling point rises above the pure solvent's value. This colligative property depends exclusively on solute particle concentration, not chemical identity. The elevation ΔTb follows the relationship ΔTb = i × Kb × m, where Kb is the solvent's ebullioscopic constant (°C·kg/mol) and m is molality. Miscalculating this shift in industrial distillation or antifreeze formulation leads to inefficient separations, thermal damage to heat-sensitive compounds, or engine coolant failure under load. Electrolytes require the van't Hoff factor i to account for dissociation - NaCl yields i = 2, while sucrose remains i = 1.

This calculator applies the standard ebullioscopic equation with a built-in database of 25 solvents including water (Kb = 0.512 °C·kg/mol), benzene, and acetic acid. Note: the model assumes ideal dilute solution behavior and breaks down at high concentrations (typically above 0.1 M) where activity coefficients deviate significantly from unity.

boiling point elevation colligative properties ebullioscopic constant molality calculator chemistry calculator solution boiling point Kb constant

Formulas

The boiling point elevation of a solution is calculated using the colligative property equation derived from Raoult's Law and the Clausius-Clapeyron relationship:

ΔTb = i × Kb × m

where ΔTb = boiling point elevation (°C), i = van't Hoff factor (number of particles per formula unit), Kb = ebullioscopic constant of the solvent (°C·kg/mol), and m = molality of the solution (mol/kg).

Molality is computed from the solute and solvent masses:

m = nsolutemsolvent (kg) = masssoluteMsolute × masssolvent (kg)

where nsolute = moles of solute, Msolute = molar mass of solute (g/mol), and masssolvent = mass of solvent in kilograms. The new boiling point equals the pure solvent's boiling point plus the elevation: Tb,new = Tb,pure + ΔTb.

Reference Data

SolventFormulaNormal Boiling Point (°C)Kb (°C·kg/mol)
WaterH₂O100.00.512
BenzeneC₆H₆80.12.53
ChloroformCHCl₃61.23.63
Acetic AcidCH₃COOH118.13.07
EthanolC₂H₅OH78.41.22
MethanolCH₃OH64.70.83
AcetoneC₃H₆O56.31.71
Carbon TetrachlorideCCl₄76.75.03
Diethyl EtherC₄H₁₀O34.62.02
Carbon DisulfideCS₂46.32.34
CyclohexaneC₆H₁₂80.72.79
TolueneC₇H₈110.63.40
NitrobenzeneC₆H₅NO₂210.95.24
PhenolC₆H₅OH181.83.56
AnilineC₆H₅NH₂184.13.69
Formic AcidHCOOH100.82.77
Ethyl AcetateC₄H₈O₂77.12.82
BromoformCHBr₃149.16.81
NaphthaleneC₁₀H₈217.95.65
CamphorC₁₀H₁₆O204.05.95
1-PropanolC₃H₇OH97.21.55
2-PropanolC₃H₇OH82.41.58
PyridineC₅H₅N115.32.69
Dimethyl SulfoxideC₂H₆OS189.03.22
AcetonitrileCH₃CN81.61.29

Frequently Asked Questions

The van't Hoff factor i represents the number of particles a solute produces upon dissolution. For non-electrolytes like sucrose or urea, i = 1. Ionic compounds dissociate: NaCl has i = 2 (Na⁺ + Cl⁻), CaCl₂ has i = 3 (Ca²⁺ + 2Cl⁻), and Fe₂(SO₄)₃ has i = 5. In practice, ion pairing at higher concentrations reduces the effective i below the theoretical maximum.
Molality remains independent of temperature because it relates moles to solvent mass, which does not change with thermal expansion. Molarity uses solution volume, which expands or contracts with temperature shifts. Since boiling point measurements involve significant temperature changes, molality provides consistent concentration values throughout the heating process.
The linear relationship ΔTb = iKbm assumes activity coefficients equal unity. This holds reasonably well below 0.1 mol/kg for most systems. Above 0.5 mol/kg, solute-solute interactions cause deviations exceeding 5%. For concentrated solutions, extended Debye-Hückel or Pitzer models incorporating ionic strength corrections become necessary.
The constant emerges from integrating the Clausius-Clapeyron equation under dilute solution conditions: Kb = RTb2Msolvent1000ΔHvap, where R = 8.314 J/(mol·K), Tb is the normal boiling point in Kelvin, Msolvent is molar mass (g/mol), and ΔHvap is the enthalpy of vaporization (J/mol). Solvents with high boiling points and low heats of vaporization exhibit larger Kb values.
Standard colligative equations assume non-volatile solutes. When the solute has appreciable vapor pressure near the solution's boiling point, both components contribute to the total vapor pressure, complicating the relationship. The measured boiling point may be lower than predicted or exhibit azeotropic behavior. For volatile solute systems, Raoult's Law for ideal mixtures or activity-based models must replace the simple Kbm treatment.
Measure ΔTb experimentally, then rearrange the equation: Msolute = i × Kb × masssoluteΔTb × masssolvent (kg). This technique works best for non-electrolytes (i = 1) in dilute solution. Precision thermometry detecting 0.01 °C differences is essential for accurate results.