Boiling Point Elevation Calculator

Dissolve something in a liquid and it boils at a higher temperature than the pure liquid would, an effect called boiling point elevation, and this calculator works out exactly how much higher. It is one of the colligative properties, the small family of effects that depend only on how many dissolved particles are present, not on what they are, and it explains a string of everyday observations: why salted water boils a touch above 100 degrees, why antifreeze raises a car coolant's boiling point as well as lowering its freezing point, and why a concentrated syrup boils hotter than plain water. The calculator uses the standard relationship, delta Tb equals i times Kb times m, and asks for three inputs. The molality, m, is the moles of solute per kilogram of solvent. The van't Hoff factor, i, is the number of particles each unit of solute breaks into when it dissolves, which is 1 for things that stay whole like sugar, about 2 for table salt as it splits into two ions, and 3 for something like calcium chloride. The boiling point constant, Kb, is a property of the solvent, set here to water's value of 0.512 degrees Celsius per molal but easily changed for other solvents. From these it returns the elevation in degrees and the new, raised boiling point. Use it for chemistry homework and exams, for lab work preparing solutions, or simply to understand why the kitchen and the road behave the way they do. It updates as you type so you can see how doubling the concentration or the particle count changes the result. The formula and a worked example are below.

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van't Hoff factor (i)

Kb (solvent constant)

Molality (m)

mol/kg

Normal boiling point

°C

1.024 °C

boiling point elevation (ΔTb)

New boiling point101.024 °C

How it works

The boiling point elevation is delta Tb equals i times Kb times m. The van't Hoff factor i counts the particles each solute unit splits into, Kb is the solvent's boiling point constant (0.512 degrees per molal for water), and m is the molality. The new boiling point is the normal boiling point plus the elevation.

Worked example

For a 1 molal solution of table salt in water, i is 2, Kb is 0.512, and m is 1. The elevation is 2 times 0.512 times 1, which is 1.024 degrees Celsius. So the water now boils at about 101.0 degrees instead of 100.

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Frequently asked questions

What is boiling point elevation?

Boiling point elevation is the rise in a liquid's boiling point when a solute is dissolved in it. Salt water, for example, boils a little above 100 degrees Celsius. It is a colligative property, meaning it depends on how many dissolved particles there are, not what they are.

What is the formula for boiling point elevation?

Delta Tb equals i times Kb times m, where i is the van't Hoff factor (the number of particles each formula unit splits into), Kb is the boiling point constant of the solvent, and m is the molality. For water, Kb is about 0.512 degrees Celsius per molal.

What is the van't Hoff factor?

The van't Hoff factor, i, is the number of particles a solute breaks into when it dissolves. Sugar stays as one particle, so i is 1. Table salt splits into a sodium and a chloride ion, so i is about 2, which doubles its effect on the boiling point.