About

Boiling point elevation is a colligative property. Adding a non-volatile solute to a solvent raises the boiling point by ΔT_b proportional to the solute's molality m and the solvent's ebullioscopic constant K_b. Miscalculating this shift causes errors in distillation column design, antifreeze formulation, and food processing where precise phase-change temperatures determine product safety and energy cost. Electrolyte solutes dissociate and multiply the effect by the van't Hoff factor i, a detail often ignored in naive calculations.

This calculator applies the standard relation ΔT_b = i ⋅ K_b ⋅ m with optional pressure correction via the Clausius-Clapeyron equation. It assumes dilute, ideal solutions. Accuracy degrades above 2 mol/kg molality or near critical pressures. Real solutions exhibit activity coefficient deviations not modeled here.

Formulas

The boiling point of a solution is determined by the elevation above the pure solvent's boiling point.

ΔT_b = i ⋅ K_b ⋅ m

Where ΔT_b = boiling point elevation (°C), i = van't Hoff factor (number of particles the solute dissociates into), K_b = ebullioscopic constant of the solvent (°C⋅kg/mol), m = molality of the solution (mol/kg).

Molality is computed from mass inputs as:

m = n_solutem_solvent (in kg)

Where n_solute = moles of solute. If mass of solute is given, n = massM where M = molar mass of solute (g/mol).

The final boiling point of the solution is:

T_b,solution = T_b,solvent + ΔT_b

For non-standard pressures, the Clausius-Clapeyron equation adjusts the pure solvent boiling point before applying the elevation:

ln(P₂P₁) = ΔH_vapR (1T₁ − 1T₂)

Where P₁ = 1 atm (reference), P₂ = actual pressure, R = 8.314 J/(mol⋅K), T₁ = normal boiling point in Kelvin, T₂ = adjusted boiling point at pressure P₂.

Reference Data

Solvent	Normal B.P. (°C)	K_b (°C⋅kg/mol)	ΔH_vap (kJ/mol)	Molar Mass (g/mol)
Water	100.0	0.512	40.7	18.015
Ethanol	78.37	1.22	38.6	46.07
Benzene	80.1	2.53	30.8	78.11
Chloroform	61.2	3.63	29.4	119.38
Acetic Acid	118.1	3.07	23.7	60.05
Diethyl Ether	34.6	2.02	26.5	74.12
Acetone	56.05	1.71	31.3	58.08
Carbon Tetrachloride	76.7	5.03	29.8	153.82
Methanol	64.7	0.785	35.2	32.04
Toluene	110.6	3.40	33.2	92.14
Cyclohexane	80.7	2.79	30.1	84.16
Carbon Disulfide	46.2	2.34	26.7	76.13
Nitrobenzene	210.9	5.24	40.8	123.11
Phenol	181.7	3.04	45.7	94.11
Naphthalene	218.0	5.80	43.3	128.17
Dimethyl Sulfoxide	189.0	3.22	43.1	78.13
Hexane	68.7	2.75	28.9	86.18
Xylene (mixed)	139.0	4.25	35.7	106.16

Frequently Asked Questions

Electrolytes dissociate into ions in solution. NaCl produces 2 particles (i = 2), CaCl₂ produces 3 (i = 3). Each particle contributes independently to boiling point elevation. Using i = 1 for NaCl underestimates ΔT_b by roughly 50%. In practice, ion pairing at high concentrations reduces the effective i below the theoretical value.

The linear relationship ΔT_b = i ⋅ K_b ⋅ m assumes ideal dilute behavior. Above approximately 1 - 2 mol/kg, solute-solute interactions become significant. Activity coefficients deviate from unity, and measured elevation exceeds or falls below the predicted value depending on the system. For concentrated solutions, use experimental activity data or Pitzer equations.

Atmospheric pressure drops roughly 12 kPa per 1000 m elevation gain. At 2000 m, water boils near 93 °C instead of 100 °C. This calculator applies the Clausius-Clapeyron correction to find the adjusted pure-solvent boiling point at your pressure before computing the solute elevation on top of that.

No. The formula assumes a non-volatile solute whose vapor pressure is negligible. Volatile solutes form a two-component vapor phase governed by Raoult's law, which can lower the boiling point or create azeotropes. This tool is restricted to non-volatile solute scenarios.

K_b is derived from the thermodynamic properties of the pure solvent: K_b = R ⋅ T_b² ⋅ MΔH_vap. A higher K_b means the solvent's boiling point is more sensitive to dissolved particles. Carbon tetrachloride (K_b = 5.03) shows roughly 10× the elevation per molal as water (0.512).

Multiple non-volatile solutes can be handled by summing total molality of all solute particles (each multiplied by its own van't Hoff factor) before multiplying by K_b. Mixed solvents are not supported because each mixture ratio changes K_b and T_b in non-trivial ways requiring experimental data.