Boiling Point Elevation Calculator
Find how much a solute raises the boiling point.
Ions per formula unit; 1 for non-electrolytes
Water = 0.512
Results update as you type.
How it works
Dissolving a solute in a liquid raises its boiling point, and this calculator finds by how much using the colligative property equation. You enter the van 't Hoff factor, the solvent's ebullioscopic constant Kb, and the solution's molality, and it returns the boiling point elevation in degrees Celsius. The effect is colligative, which means it depends only on how many solute particles are dissolved, not what they are: a mole of sugar and a mole of any other non-dissociating molecule raise the boiling point equally. The van 't Hoff factor accounts for solutes that split into ions, such as salt, which produces two particles per formula unit and therefore doubles the effect. Kb is a constant specific to each solvent; for water it is 0.512 degrees Celsius per molal. This principle explains why salted water boils at a slightly higher temperature and is the same family of effects behind antifreeze and road salt. Students study it in general chemistry, and it has practical uses in cooking and industry. Add the calculated elevation to the pure solvent's normal boiling point to find the solution's boiling point. Enter the three values to compute the rise.
ΔTb = i · Kb · m
Boiling point elevation is a colligative property, meaning it depends on the number of dissolved particles rather than their identity. The rise in boiling point equals the van 't Hoff factor, which counts how many particles each formula unit releases, times the ebullioscopic constant of the solvent, times the molality of the solution. Multiplying these gives the increase in boiling temperature above that of the pure solvent.
Source:Chemistry (colligative properties)
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter van 't hoff factor (i), kb (ebullioscopic constant) and molality.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Boiling point rise (ΔTb) updates instantly as you type — no button to press.
Frequently asked questions
What is boiling point elevation?
Boiling point elevation is the increase in a liquid's boiling point that occurs when a solute is dissolved in it. It is a colligative property, depending on the number of dissolved particles rather than their chemical nature. The more solute particles present, the higher the boiling point rises above that of the pure solvent, following the equation ΔTb equals i times Kb times molality.
What is the van 't Hoff factor?
The van 't Hoff factor, written i, is the number of particles a solute produces when it dissolves. Non-electrolytes like sugar do not dissociate, so their factor is 1. Ionic compounds split into ions: table salt gives about 2 and calcium chloride about 3. A higher factor means more particles and a larger effect on colligative properties like boiling point elevation.
What is Kb?
Kb is the ebullioscopic constant, a property unique to each solvent that quantifies how strongly its boiling point rises per unit of molality. For water it is 0.512 degrees Celsius per molal. Multiplying Kb by the molality and the van 't Hoff factor gives the total boiling point elevation. Different solvents have different Kb values, so use the correct one for your solvent.
Why does salt make water boil hotter?
Dissolved salt ions interfere with the water molecules' ability to escape into vapour, so the solution must reach a higher temperature before its vapour pressure equals atmospheric pressure and it boils. Because salt dissociates into two ions, it roughly doubles the particle count compared with a non-electrolyte, producing a noticeable, though modest, rise in boiling temperature.
How do I find the solution's boiling point?
Add the calculated boiling point elevation to the pure solvent's normal boiling point. For water at standard pressure that is 100 degrees Celsius, so an elevation of 1.02 degrees gives a solution boiling point of about 101.02 degrees. The calculator gives you the elevation; simply add it to the solvent's known boiling point to get the final value.