Created By : Rina Nayak

Reviewed By : Phani Ponnapalli

Last Updated : May 15, 2023

This Molality Calculator finds the molality of the given solution. This online calculator allows taking the number of moles of solute, and weight of the solvent in kgs to produce the molality as the answer.

Moles of Solute
Mass of Solvent

Molality Definition | Molality Formula

Molality or molar concentration is defined as the ratio of the amount of solute present to the weight of the solvent in the solution. It is the property of a chemical solution. The molality of a solution is used as its value doesn't change with the temperature change.

The molality formula is as follows:

Molaity M = (Number of moles of solute)/Weight of solvent in Kg.

The SI unit to denote molality is mol/kg.

Difference Between Molarity and Molality

Both Molality and Molarity are similar topics they are used to measure the concentration of the solution. The main differences between them are tabulated here:

Molality Molarity
The symbol used is m or b. The symbol used is M.
Defined as the ratio of solute in moles to the mass of solvent in kg. Defined as the substance in moles divided by the volume in litres of the solution.
Unit is mol/kg Unit is mol/L
Accurate but rarely used. More popular and particular use in lab.
Independent of temperature and pressure. Temperature and pressure dependent.

The relation between Molality and Molarity can be explained by this equation:

M = m * d / (1 + (m * W))


M is the molarity

m is the molality

W is the molar weight of the solute

d is the mass density of a solution.

How to Calculate Molality of a Solution?

  • Choose any chemical substance.
  • Calculate the molar mass of the solvent.
  • The moles of the solute can be find using the formula moles = mass of solute/molar mass.
  • Put moles, and mass values in the molality formula to get the answer.


Calculate the molality of the solution where 0.5 g of toluene C7H8 is dissolved in 225 g of Benzene C6H6.


Find the moles for the given solute.

Toluence molar mass C7H8 = 7 * 12 + 1 * 8 = 92 moles/gram

Moles of Toluence = mass in grams/molar weight

= 0.054 mole.

Weight of the solvent = 225 g of Benzene/1000

= 0.225 kg

Molality m = Moles of Toluence/ Mass of Benzene

= 0.054/0.225

= 0.24 moles/kg

Therefore, the molality of solution is 0.24 moles/kg.

FAQ's on Online Molality Calculator

1. What is a molality example?

Molality is defined as the number of moles of solute present in 100 grams of the solvent. The exam is 1 molal NaOH solution represents a solution with 1 mole of NaOH in 1 Kg of water.

2. How do you solve molality step by step?

To find the molality of a chemical solution, follow these steps.

  • Write the molality formula.
  • Identify the solute and solvent in the solution.
  • Calculate the moles of the solute, and mass of the solvent.
  • The ratio of solute moles to the weight of the solvent is the solution molality.

3. What is molality equal to?

The molality of a chemical solution is equal to the ratio of the moles of the solute to the weight of the solvent in kilograms.

4. Is molality and mole fraction the same?

The molality is defined as the total number of moles of the solute contained in a kg of solvent. Mole fraction is defined as the ratio of the number of moles of the component in the solution to the total number of moles of all components in the solution.