Case 1
- Van 't Hoff factor i
- 2
- Ebullioscopic constant Kb
- 0.512K·kg/mol
- Molality b
- 1mol/kg
1.024K
Open with these valuesBoiling Point Elevation Calculator
1.024K
Result: 1.024 KDissolved particles raise the boiling point: ΔTb = i × Kb × b. One molal table salt in water gives 2 × 0.512 × 1 = 1.024 K, so the pot boils at about 101.024 °C. The result is a difference, so kelvin and degrees Celsius are the same number here.
The numbers at a glance
Held fixed: Van 't Hoff factor i 2.00, Ebullioscopic constant Kb 0.512 K·kg/mol.
| Molality b (mol/kg) | Result (K) |
|---|---|
| 0.000 | 0.000 |
| 0.250 | 0.256 |
| 0.500 | 0.512 |
| 0.750 | 0.768 |
| 1.000Your value | 1.024 |
| 1.250 | 1.280 |
| 1.500 | 1.536 |
| 1.750 | 1.792 |
| 2.000 | 2.048 |
Worked examples
Case 2
- Van 't Hoff factor i
- 1
- Ebullioscopic constant Kb
- 0.512K·kg/mol
- Molality b
- 1mol/kg
0.512K
Open with these valuesCase 3
- Van 't Hoff factor i
- 3
- Ebullioscopic constant Kb
- 0.512K·kg/mol
- Molality b
- 0.5mol/kg
0.768K
Open with these valuesHow it's calculated
ΔTb = i × Kb × b
- StepEnter how many particles one formula unit splits into: 1 sugar, 2 NaCl, 3 CaCl₂.
- StepEnter the ebullioscopic constant of the solvent; water is 0.512 K·kg/mol.
- StepEnter the molality — moles of solute per kilogram of solvent.
- ResultRead the elevation, then add it to the solvent's own boiling point.
Reference table
| i, Kb, b | What is dissolved | Elevation in K |
|---|---|---|
| 2, 0.512, 0 | nothing — pure water | 0.000 |
| 1, 1.86, 0.25 | a solvent with Kb = 1.86 | 0.465 |
| 1, 0.512, 1 | 1 molal sugar in water | 0.512 |
| 3, 0.512, 0.5 | 0.5 molal calcium chloride | 0.768 |
| 2, 0.512, 1 | 1 molal table salt in water | 1.024 |
| 2, 0.512, 2 | 2 molal table salt in water | 2.048 |
Questions
How do I calculate boiling point elevation?
Multiply the van 't Hoff factor by the ebullioscopic constant and the molality: ΔTb = i × Kb × b. One molal NaCl in water is 2 × 0.512 × 1 = 1.024 K.
What is the van 't Hoff factor i?
It is how many particles one formula unit of the solute breaks into when it dissolves: 1 for non-electrolytes such as sugar, 2 for NaCl, 3 for CaCl₂. More particles mean a bigger elevation, which is why this calculator asks for it rather than assuming a substance.
What is the ebullioscopic constant Kb?
It is a property of the solvent that links molality to the rise in boiling point. Water is 0.512 K·kg/mol; benzene is about 2.53 and ethanol about 1.07, so always use the constant of the solvent you actually have.
Why molality and not molarity?
Molality counts moles per kilogram of solvent, and a mass does not change when the solution is heated. Molarity is per litre of solution, and that volume does change near the boiling point.
Is the answer in kelvin or degrees Celsius?
Both, because it is a temperature difference and the two scales have the same step size. An elevation of 1.024 K is 1.024 °C, so salty water boils at about 101.024 °C instead of 100 °C.
Sources and last check
Information, not professional advice.