Molality Calculator
Calculate solution molality from solute mass, molar mass, and solvent mass. Get instant mol/kg results with automatic unit conversions.
Calculate Molality
Enter the solute mass, molar mass, and solvent mass to calculate the molality of the solution.
What Is a Molality Calculator?
A Molality Calculator calculates the concentration of a solution using the number of moles of solute and the mass of the solvent in kilograms.
Molality is commonly represented by the lowercase letter m and expressed as mol/kg. Unlike molarity, molality depends on the mass of the solvent rather than the volume of the complete solution.
Molality Formula
The standard equation used to calculate molality is:
m = n ÷ kg of solvent
Here, m represents molality and n represents moles of solute.
If you have the mass of the solute rather than its number of moles, calculate moles first:
n = Mass of Solute (g) ÷ Molar Mass (g/mol)
This calculator automatically performs both calculations.
How to Use the Molality Calculator
Enter Solute Mass
Enter the mass of the solute and select grams, milligrams, or kilograms.
Enter Molar Mass and Solvent Mass
Provide the molar mass in g/mol, then enter the mass of the solvent and select its unit.
Calculate the Result
Click Calculate Molality to get the final concentration in mol/kg and see the intermediate values.
Molality Calculation Example
Suppose 10 grams of sodium chloride (NaCl) are dissolved in 500 grams of water. The molar mass of NaCl is approximately 58.44 g/mol.
Step 1: Calculate Moles
Step 2: Convert the Solvent to Kilograms
Step 3: Calculate Molality
Therefore, the molality of the solution is approximately 0.342 mol/kg.
Solute, Solvent, and Solution
Solute
The solute is the substance being dissolved, such as salt when making a saltwater solution.
Solvent
The solvent is the substance that dissolves the solute. Water is one of the most common solvents.
Solution
A solution is the homogeneous mixture formed when a solute is dissolved in a solvent.
Molality vs. Molarity
Molality and molarity both describe concentration, but they use different measurements.
| Property | Molality | Molarity |
|---|---|---|
| Symbol | m | M |
| Formula | Moles / kg solvent | Moles / L solution |
| Unit | mol/kg | mol/L |
| Based On | Mass of solvent | Volume of solution |
| Temperature Effect | Generally unchanged by volume expansion | Can change as solution volume changes |
Why Is Molality Important?
Molality is useful because it depends on mass instead of volume. The mass of a sample does not change simply because its temperature changes, while liquid volume can expand or contract.
Freezing Point Depression
Molality is commonly used when studying how dissolved particles lower the freezing point of a solvent.
Boiling Point Elevation
It is also useful when calculating how a nonvolatile solute changes the boiling point of a solvent.
Colligative Properties
Many chemistry calculations involving colligative properties use molality because it provides a mass-based concentration measurement.
Important Mass Conversions
| Unit | Equivalent |
|---|---|
| 1 kilogram | 1,000 grams |
| 1 gram | 1,000 milligrams |
| 1 pound | 0.45359237 kilograms |
| 1 milligram | 0.001 grams |
Frequently Asked Questions
Molality is the number of moles of solute divided by the mass of the solvent in kilograms.
Molality = moles of solute ÷ kilograms of solvent.
Molality is commonly expressed as moles per kilogram, written as mol/kg.
Divide the mass of the solute in grams by its molar mass in grams per mole.
No. Molality uses kilograms of solvent, while molarity uses liters of the complete solution.
Because molality is based on mass, it is generally not directly affected by temperature-related volume changes.
Use only the mass of the solvent in kilograms when calculating molality.
Calculate Molality Quickly and Accurately
Use this Molality Calculator to determine solution concentration from solute mass, molar mass, and solvent mass. The tool automatically handles mass conversions and provides the final concentration in mol/kg.