Boiling Point Elevation Calculator
ChemistryCalculate boiling point elevation for solutions using ΔTb = Kb × m × i. Enter solvent, solute mass, and molality to find the new boiling point of any solution.
0.512
Boiling Point Elevation ΔTb (°C)
0.512
New Boiling Point (°C)
100.512
New Boiling Point (K)
373.662
What is a BP Elevation?
The Boiling Point Elevation Calculator computes the increase in boiling point when a solute is dissolved in a solvent, using the colligative property formula ΔTb = Kb × m × i. Enter the solvent (with its preset ebullioscopic constant Kb), the molality of the solution, and the van't Hoff factor for the solute to get the boiling point elevation and the new boiling point of the solution.
Boiling point elevation is one of four colligative properties — properties that depend on the concentration of dissolved particles, not their chemical identity. The other three are freezing point depression (computed by the Freezing Point Depression Calculator), osmotic pressure, and vapour pressure lowering.
The mechanism: dissolved solute particles lower the vapour pressure of the solution compared to the pure solvent (Raoult's law). Since boiling requires vapour pressure to equal atmospheric pressure, a higher temperature is needed to achieve the same vapour pressure — hence the boiling point rises. The elevation is directly proportional to the molality of dissolved particles (m × i), making it a useful analytical tool for determining molar masses of unknown solutes and for designing coolant systems.
How to use this BP Elevation calculator
- Select the solvent from the Solvent dropdown. The preset Kb value is shown next to each solvent name. For a custom solvent, select Custom Kb and enter the Kb value.
- Enter the Molality in mol/kg — this is moles of solute dissolved per kilogram of solvent (not per litre of solution). For 5.85 g of NaCl in 100 g of water: moles NaCl = 5.85/58.5 = 0.1 mol; kg solvent = 0.1 kg; molality = 1.0 mol/kg.
- Enter the van't Hoff Factor (i): 1 for non-electrolytes, 2 for NaCl or KCl, 3 for CaCl₂ or Na₂SO₄, etc. For weak electrolytes, calculate i from the degree of dissociation α: i = 1 + (n−1)α where n is the number of ions.
- Read ΔTb and the New Boiling Point in °C.
- Compare the new boiling point to the pure solvent boiling point to verify the elevation is in the expected range.
Formula & Methodology
Boiling point elevation:ΔTb = Kb × m × i T_b(solution) = T_b(solvent) + ΔTbCommon solvent Kb values: | Solvent | Normal BP (°C) | Kb (°C·kg/mol) | |---|---|---| | Water | 100.0 | 0.512 | | Ethanol | 78.4 | 1.22 | | Benzene | 80.1 | 2.53 | | Camphor | 204.0 | 5.61 | Worked example — NaCl solution for cooking: 50 g NaCl dissolved in 500 g (0.5 kg) water. NaCl molar mass = 58.5 g/mol. Molality = (50/58.5)/0.5 = 1.71 mol/kg. i = 2 (strong electrolyte).ΔTb = 0.512 × 1.71 × 2 = 1.75°C New boiling point = 100 + 1.75 = 101.75°CIn food processing, sugar concentration is more significant: 1 kg sucrose (342 g/mol) dissolved in 1 kg water: m = 2.92 mol/kg, i = 1. ΔTb = 0.512 × 2.92 = 1.50°C. This elevation is carefully controlled in confectionery (toffee, caramel) to achieve the desired sugar crystal structure.
Frequently Asked Questions
Boiling point elevation is a colligative property — the phenomenon where dissolving a non-volatile solute in a solvent raises the solution's boiling point above that of the pure solvent. The elevation occurs because the solute particles lower the vapour pressure of the solution (Raoult's law), so a higher temperature is required to raise the vapour pressure to equal atmospheric pressure. The elevation depends only on the number of dissolved particles, not their chemical identity.
The boiling point elevation is ΔTb = Kb × m × i, where Kb is the ebullioscopic constant of the solvent (°C·kg/mol), m is the molality of the solution (mol solute per kg solvent), and i is the van't Hoff factor (number of particles the solute dissociates into). For a non-electrolyte like glucose, i = 1. For NaCl (which dissociates into Na⁺ and Cl⁻), i = 2. For CaCl₂ (Ca²⁺ + 2Cl⁻), i = 3. The new boiling point is T_b(solution) = T_b(solvent) + ΔTb.
The ebullioscopic constant Kb (also called the boiling point elevation constant or molal elevation constant) is a solvent-specific property that quantifies how much 1 mol/kg of non-electrolyte solute raises the boiling point. For water, Kb = 0.512 °C·kg/mol. For benzene, Kb = 2.53 °C·kg/mol. For camphor, Kb = 5.61 °C·kg/mol (unusually high, making camphor useful for determining molar masses by the Rast method). The higher the Kb, the larger the boiling point elevation per molal concentration.
The van't Hoff factor i represents the number of particles a solute formula unit produces when dissolved. For non-electrolytes (glucose, sucrose, urea): i = 1. For strong electrolytes: NaCl → i = 2, MgCl₂ → i = 3, Al₂(SO₄)₃ → i = 5 (theoretically). In practice, ion-pairing and activity effects make i slightly less than the ideal value at higher concentrations. For weak electrolytes, i is between 1 and the maximum, depending on degree of dissociation.
Vehicle coolant (typically 50% ethylene glycol in water) uses both boiling point elevation and freezing point depression. The ethylene glycol raises the boiling point of water from 100°C to about 108°C at 50% concentration, preventing coolant from boiling in hot conditions. Simultaneously, it depresses the freezing point to about −37°C, preventing freeze damage in cold climates. This dual colligative property protection explains why antifreeze is essential in both hot (Rajasthan summers) and cold (Himalayan winters) climates.
Select the solvent from the dropdown (Water, Benzene, Camphor, Ethanol, or Custom Kb). Enter the molality in mol/kg — this is moles of solute per kilogram of solvent (not per litre of solution). Enter the van't Hoff factor i: use 1 for non-electrolytes, 2 for 1:1 electrolytes like NaCl, 3 for 1:2 electrolytes like CaCl₂. The calculator returns ΔTb and the new boiling point in °C and K.
Molality (m) is moles of solute per kilogram of solvent — it does not change with temperature because it is mass-based. Molarity (M) is moles of solute per litre of solution — it changes with temperature because volume changes with thermal expansion. Colligative property calculations (boiling point elevation, freezing point depression, osmotic pressure) all use molality because it is temperature-independent and because these properties depend on the mole ratio of solute to solvent, not on concentration per unit volume.
Yes — this is the ebullioscopic method for molar mass determination. By dissolving a known mass of solute in a known mass of solvent and measuring ΔTb, the molality m = ΔTb / Kb, and molar mass M = (mass of solute in grams) / (m × mass of solvent in kg). This method is most accurate for non-electrolytes in solvents with high Kb like camphor (Kb = 5.61 °C·kg/mol) — the Rast method — since it gives a larger, more measurable ΔTb per mol/kg.
Seawater contains approximately 35 g of dissolved salts per kg of water (35 ppt salinity), predominantly NaCl (≈27.2 g/kg). The effective molality of ions in seawater is approximately 1.1 mol/kg (considering i ≈ 1.87 for NaCl at sea salinity). Boiling point elevation: ΔTb = 0.512 × 1.1 = 0.56°C. Seawater boils at approximately 100.56°C at sea level — a small but measurable elevation relevant in desalination plant design and maritime food preparation.
Yes — adding salt to pasta or rice cooking water raises the boiling point, but only marginally. Adding 10 g of NaCl to 1 litre of water (molality ≈ 0.17 mol/kg, i = 2): ΔTb = 0.512 × 0.17 × 2 ≈ 0.17°C. The effect on cooking time is negligible. However, adding salt to pasta water is still recommended for flavour, not for changing cooking temperature. Much larger quantities of solute (like sugar syrups) show meaningful elevations: 60% sucrose solution (≈14.6 mol/kg) raises the boiling point by about 7.5°C.