Boiling Point Elevation Calculator — ΔTb = Kb × m × i

Adding solute to a solvent raises its boiling point. This isn't intuition — it's a fundamental colligative property that depends only on how many dissolved particles are present, not on what they are. The CalcHub Boiling Point Elevation Calculator takes the arithmetic off your hands so you can focus on understanding what's actually happening in the solution.

The Formula

ΔTb = Kb × m × i

Where:

• ΔTb = boiling point elevation (°C or K)


• Kb = ebullioscopic constant of the solvent (°C·kg/mol)


• m = molality of the solution (mol of solute / kg of solvent)


• i = van't Hoff factor (number of particles the solute dissociates into)

The new boiling point = normal boiling point + ΔTb.

Common Solvent Kb Values

Solvent	Normal Boiling Point (°C)	Kb (°C·kg/mol)
Water	100.0	0.512
Benzene	80.1	2.53
Ethanol	78.4	1.22
Cyclohexane	80.7	2.79
Acetone	56.0	1.71

Van't Hoff Factor (i)

This is what separates ionic compounds from molecular ones:

Solute	Dissociation	i
Glucose (C₆H₁₂O₆)	None	1
NaCl	Na⁺ + Cl⁻	2
CaCl₂	Ca²⁺ + 2Cl⁻	3
Al₂(SO₄)₃	2Al³⁺ + 3SO₄²⁻	5

Note that real solutions don't always achieve theoretical i values due to ion pairing. At higher concentrations, i is effectively lower.

How to Use the Calculator

1. Open CalcHub and select the Boiling Point Elevation Calculator.
2. Enter the solute molality (mol/kg of solvent).
3. Enter Kb for your solvent (or select from the dropdown).
4. Enter the van't Hoff factor for the solute.
5. The calculator returns ΔTb and the new boiling point.

Worked Example

What is the boiling point of a solution containing 58.44 g of NaCl in 500 g of water?

Moles of NaCl = 58.44 g ÷ 58.44 g/mol = 1.0 mol
Molality = 1.0 mol ÷ 0.5 kg = 2.0 mol/kg
i for NaCl = 2
ΔTb = 0.512 × 2.0 × 2 = 2.048°C
New boiling point = 100 + 2.048 = 102.05°C

Practical Notes

• Cooking pasta in salted water? The salt does raise the boiling point — by about 0.5°C for typical cooking salt quantities. Not enough to cook faster, but it's textbook-accurate.
• Antifreeze (ethylene glycol) works in both directions — it raises boiling point and lowers freezing point simultaneously, which is why it's in radiators year-round.

---

Is boiling point elevation a colligative property?

Yes. Colligative properties depend on the number of dissolved particles, not their identity. That's why 1 mol of NaCl has twice the effect of 1 mol of glucose — NaCl produces two ions.

What's the relationship between boiling point elevation and vapor pressure?

Dissolved non-volatile solutes lower the vapor pressure of the solution (Raoult's Law). A lower vapor pressure means the solution needs to be heated to a higher temperature to reach 1 atm — hence the higher boiling point. The two phenomena are directly connected.

Can I use this for non-aqueous solvents?

Yes, as long as you use the correct Kb for that solvent. The formula is the same; just swap in the appropriate ebullioscopic constant from the table above or look it up for your specific solvent.

---

Related calculators: Freezing Point Calculator · Molarity Calculator · Ideal Gas Calculator