Boiling Point Elevation Calculator

Last updated: April 5, 2026

The Boiling Point Elevation Calculator computes the rise in a solvent's boiling point when a solute is dissolved using ΔTb = Kb × m × i. This colligative property depends on dissolved particle concentration — governing antifreeze formulation, food chemistry, and pharmaceutical manufacturing.

Calculator

Solvent Preset

Van't Hoff Factor (i)

Molality (m)mol/kg

Custom Ebullioscopic Constant (Kb)°C·kg/mol

Custom Pure Solvent Boiling Point°C

Results

Kb Used

0.512

°C·kg/mol

Pure Solvent Boiling Point Used

100

°C

Boiling Point Elevation (ΔTb)

0.512

°C

Solution Boiling Point

100.51

°C

Elevation per Molal

0.512

°C per mol/kg

Results

Kb Used

0.512

°C·kg/mol

Pure Solvent Boiling Point Used

100

°C

Boiling Point Elevation (ΔTb)

0.512

°C

Solution Boiling Point

100.51

°C

Elevation per Molal

0.512

°C per mol/kg

When you dissolve a non-volatile solute in a solvent, the boiling point rises. This is not because the solute adds heat — it is because dissolved particles reduce the solvent's tendency to vaporize, requiring a higher temperature to generate the vapor pressure needed for boiling. This boiling point elevation is a colligative property: it depends only on the concentration of solute particles, not what they are. The boiling point elevation calculator handles both electrolytes and non-electrolytes.

Boiling Point Elevation Formula

ΔTb = Kb × m × i

where: Kb = molal boiling point elevation constant (°C·kg/mol); m = molality (moles of solute per kg of solvent); i = van't Hoff factor (number of particles per formula unit).

Van't Hoff factors: non-electrolytes (sugar, urea, alcohol) i = 1; NaCl → Na⁺ + Cl⁻, i = 2; CaCl₂ → Ca²⁺ + 2Cl⁻, i = 3; AlCl₃, i = 4. Kb values: water = 0.512 °C·kg/mol; benzene = 2.53; ethanol = 1.22; acetic acid = 3.07; cyclohexane = 2.75.

Example: 100 g NaCl in 2 kg water: m = 1.71 mol/kg; i = 2; ΔTb = 0.512 × 1.71 × 2 = 1.75°C. New boiling point = 101.75°C. Use this online calculator for any solute-solvent combination.

Practical Applications

Antifreeze (ethylene glycol in water): raises boiling point to prevent coolant from boiling in hot engines (typically to 106–115°C with standard concentrations)
Food processing: sugar solutions used in jam and candy making boil at elevated temperatures (a 65% sugar syrup boils at approximately 104°C), enabling higher cooking temperatures for texture development
Pharmaceutical manufacturing: controlling solution boiling points in evaporation and crystallization processes
Distillation: understanding how dissolved solutes affect distillation temperatures and fraction purity

The boiling point calculator and altitude boiling point calculator cover the complete phase change toolkit.

Ebullioscopy: Measuring Molar Mass from Boiling Point Elevation

Historically, boiling point elevation (ebullioscopy) was used to determine unknown molar masses: weigh a known mass of unknown solute, dissolve in a known mass of solvent, measure the boiling point elevation. Then: molar mass M = (Kb × mass_solute × i) / (ΔTb × mass_solvent_kg). This technique has been largely replaced by mass spectrometry and NMR, but remains a useful exercise in physical chemistry education and can be applied when only simple temperature measurements are available.

Visual Analysis

How It Works

Enter solute mass (g), solute molar mass (g/mol), solvent mass (kg), Kb of solvent (default 0.512 for water), and van't Hoff factor i. Molality m = (mass_solute/molar_mass) / mass_solvent_kg. ΔTb = Kb × m × i. New boiling point = normal boiling point + ΔTb. Optional: calculate molar mass from measured ΔTb (ebullioscopy mode).

Understanding Your Results

The boiling point elevation (ΔTb) shows how many degrees the boiling point rises above the pure solvent's boiling point. A larger ΔTb results from higher solute concentration or solutes that dissociate into more particles. The new boiling point is the temperature at which the solution will boil at standard pressure. Note that this formula is most accurate for dilute solutions; at high concentrations, deviations from ideal behavior become significant.

Worked Examples

Salt Water (NaCl in water, 1 molal)

Inputs

Kb0.512

molality1

bp solvent100

Results

delta tb1.024

new bp101.024

A 1 molal NaCl solution boils at 101.02°C. NaCl dissociates into Na⁺ and Cl⁻ (i=2), doubling the effect compared to a non-electrolyte at the same molality.

Glucose in Water (0.5 molal)

Inputs

Kb0.512

molality0.5

bp solvent100

Results

delta tb0.256

new bp100.256

Glucose is a non-electrolyte (i=1), so a 0.5 molal solution only raises the boiling point by 0.256°C. This small effect demonstrates why boiling point elevation is often difficult to observe in cooking.

Frequently Asked Questions

Boiling point elevation is the increase in a solvent's boiling point when a non-volatile solute is dissolved in it. It happens because dissolved solute particles lower the chemical potential of the solvent — they reduce the solvent's tendency to escape into the vapor phase (entropy effect). To achieve the same vapor pressure needed for boiling, the solution must be heated to a higher temperature than the pure solvent. The elevation depends only on the number of dissolved particles (concentration), not on what the solute is — hence it is a colligative property. Formula: ΔTb = Kb × m × i, where Kb is the solvent's ebullioscopic constant, m is molality, and i is the van't Hoff factor.

The van't Hoff factor (i) is the number of particles a solute produces per formula unit when dissolved. Non-electrolytes that dissolve without dissociation: sugar, urea, glucose, alcohol → i = 1. Strong electrolytes that fully dissociate: NaCl → Na⁺ + Cl⁻ → i = 2; KBr → i = 2; MgCl₂ → Mg²⁺ + 2Cl⁻ → i = 3; CaCl₂ → Ca²⁺ + 2Cl⁻ → i = 3; AlCl₃ → Al³⁺ + 3Cl⁻ → i = 4; Na₂SO₄ → 2Na⁺ + SO₄²⁻ → i = 3. Weak electrolytes have i between 1 and their maximum dissociation value (e.g., acetic acid i ≈ 1.01–1.05 at typical concentrations). In practice, ion-ion interactions at high concentrations reduce the effective van't Hoff factor below the theoretical value.

The molal boiling point elevation constant (Kb) for water is 0.512 °C·kg/mol. This means that 1 mole of non-electrolyte solute dissolved in 1 kg of water raises the boiling point by 0.512°C. For comparison, other common solvents: benzene Kb = 2.53; acetic acid = 3.07; cyclohexane = 2.75; acetone = 1.71; ethanol = 1.22; chloroform = 3.63. Solvents with weaker intermolecular forces (and therefore lower boiling points) tend to have larger Kb values, making them more sensitive to dissolved solutes.

Technically yes, but the effect is negligible at cooking concentrations. For pasta water with 10 g NaCl per liter (a generous amount): m = 0.171 mol/kg, i = 2; ΔTb = 0.512 × 0.171 × 2 = 0.175°C. The water boils at 100.175°C instead of 100°C — a difference that has no practical effect on cooking time. To raise the boiling point by a meaningful 1°C, you would need approximately 58 g of NaCl per kg of water — roughly equivalent to seawater saltiness, which would make pasta inedible. Salt is added to pasta water purely for flavor, not to raise the boiling point or cook faster.

Ethylene glycol antifreeze exploits both boiling point elevation and freezing point depression (the other major colligative property) to protect car engines. At 50% ethylene glycol by volume in water: freezing point depression of approximately 37°C (protects to −37°C); boiling point elevation of approximately 6°C (raises coolant boiling point to approximately 106°C at sea level). When combined with a pressurized cooling system (typically 15 psi / 103 kPa above ambient), the effective boiling point of the coolant rises to approximately 125–130°C — well above typical engine operating temperatures of 90–105°C. Without this boiling point elevation and pressurization, the coolant would boil in hot spots near the engine block, causing vapor lock and overheating.

This technique is called ebullioscopy. Procedure: dissolve a known mass (w₂ grams) of the unknown compound in a known mass (w₁ kg) of pure solvent; measure the boiling point elevation ΔTb precisely; calculate: molar mass M₂ = (Kb × w₂ × i) / (ΔTb × w₁). For a non-electrolyte (i=1): if 2.5 g of an unknown compound dissolved in 100 g of benzene (Kb = 2.53) raises the boiling point by 0.65°C: M₂ = (2.53 × 2.5 × 1) / (0.65 × 0.100) = 97 g/mol. This method was widely used before modern spectroscopic techniques and is still useful in physical chemistry laboratories as a hands-on demonstration of colligative properties.

Sources & Methodology

Atkins, P., de Paula, J. (2014). Atkins' Physical Chemistry, 10th ed. Oxford. Levine, I.N. (2009). Physical Chemistry, 6th ed. McGraw-Hill. CRC Handbook of Chemistry and Physics, 104th ed. (2023).

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How It Works

Understanding Your Results

Worked Examples

Salt Water (NaCl in water, 1 molal)

Inputs

Kb0.512

molality1

bp solvent100

Results

delta tb1.024

new bp101.024

A 1 molal NaCl solution boils at 101.02°C. NaCl dissociates into Na⁺ and Cl⁻ (i=2), doubling the effect compared to a non-electrolyte at the same molality.

Glucose in Water (0.5 molal)

Inputs

Kb0.512

molality0.5

bp solvent100

Results

delta tb0.256

new bp100.256

Frequently Asked Questions