Use the boiling point elevation calculator to find the change in the boiling point of a solution and its new boiling point.

To make it easier to understand the results of the boiling point elevation calculator, in the article below, we discuss:

  • What boiling point elevation is.
  • How the boiling point of a pure solvent is affected by the addition of solute.
  • The boiling point elevation formula.
  • The van 't Hoff factor and ebullioscopic constant, both of which are present in this formula.
  • You'll also find a boiling point elevation example demonstrating how to utilize this tool.

If you were looking physical version of the elevation tool, then our elevation angle calculator is probably the one you need.

Boiling point elevation definition

The boiling point is the temperature at which a liquid substance changes to its gaseous phase. This happens when the vapor pressure of a liquid equals the pressure of the surroundings. The higher the vapor pressure at the given temperature, the lower the liquid's boiling point.

Remember that vapor pressure indicates a substance's capacity to bond to itself. Thus, lower vapor pressures result in stronger intermolecular forces, then more energy to separate the molecules and convert them to their gaseous phase.

To learn how to calculate the boiling point, you can check our boiling point calculator

The term boiling point elevation refers to the increase in a solution's boiling point due to the addition of a solute  — A solution has a higher boiling point than a pure solvent.

The boiling point elevation is a colligative property, which means that it is primarily determined by the number of dissolved particles in the solution rather than its chemical composition. The boiling point elevation increases with the number of dissolved particles. In other words, the boiling point elevation rises in proportion to the solutions' concentration — This is why it takes longer to bring to boil salted water than plain water.

But why does adding a solute to a solution raise its boiling point? This is related to the fact that non-volatile solutes have a vapor pressure of zero. Then, the more solute we add to the solution, the further we decrease its vapor pressure. As mentioned, lower vapor pressures result in higher boiling temperatures because more energy is required to separate the molecules.

Boiling point elevation formula — The van 't Hoff factor and the ebullioscopic constant

To determine the value of the increase in the boiling point, we use the following boiling point elevation formula:

ΔT=iKbm\small \Delta T = i \cdot K_b \cdot m

where:

  • ΔT\Delta T — Boiling point elevation in °C;
  • ii — Van 't Hoff factor which is dimensionless;
  • KbK_b — Ebullioscopic constant in °C⋅kg/mol; and
  • mm — Molal concentration of the solution in mol/kg.

Not sure how to determine the molality of a solution? Then check out the molality calculator to find out!

To find the new boiling point of the solution TsolutionT_{solution}, simply add the boiling point elevation ΔT\Delta T obtained from the equation above to the boiling point of the pure solvent TsolventT_{solvent}:

Tsolution=Tsolvent+ΔT\small T_{solution} = T_{solvent} + \Delta T

The van 't Hoff factor ii describes the ratio between particles produced due to dissolving a substance and the mass of the substance dissolved. The value of the van 't Hoff factor is one (1) for most non-electrolytes dissolved in water. In the table below, you can find some common values of van 't Hoff factor:

Solution

Van 't Hoff factor

Sugar in water

1

Sodium chloride (NaCl) in water

1.9 or 2

Calcium chloride (CaCl2) in water

2.9 or 3

The ebullioscopic constant KbK_b also has different values depending on the solvent. Some of them are listed below:

Solvent

Ebullioscopic constant [°C⋅kg/mol]

Water

0.512

Phenol

3.04

Acetic acid

3.07

Napthalene

5.8

Benzene

2.53

How to use the boiling point elevation calculator

Let's look at how to use the boiling point elevation calculator to determine the boiling point elevation and a solution's boiling point:

  1. In the T_solvent row, indicate the boiling point of the pure substance.

  2. Enter the ebullioscopic constant or boiling point elevation constant, Kb.

  3. In the Molality (m) row, input the molality of the solution.

  4. After these are entered, the calculator will indicate the boiling point elevation ΔT and the boiling point of the solution T_solution.

By clicking on the Advanced mode of the calculator, you'll be able to select from a list of some common solvents that already have information prefilled.

Now, let us look at a boiling point elevation example to see how this works. Imagine we want to get the boiling point of a solution of salt (NaCl) dissolved in water, with a molality of 3 mol/kg. We do the following:

  1. First, we change to the Advanced mode of the calculator.

  2. From the first row, Solvents, we pick Water.

  3. The calculator will fill in the remaining fields and return preliminary results for the boiling point elevation and solution's boiling point.

  4. To adjust these calculations to fit our problem, let's change the Molality from 1 to 3 and the van 't Hoff factor from 1 to 2.

  5. The calculator will display our answers. A Boiling point elevation of 3.072 °C and a Boiling point of solution of 103.07 °C.

Gabriela Diaz
Boiling point of pure solvent (T_solvent)
°F
Ebullioscopic constant (K_b)
°C⋅
lb
/mol
Molality (m)
mol/
lb
Boiling point elevation (ΔT)
°F
Boiling point of solution (T_solution)
°F
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