Molality
Calculator
Results
- Molality (mol/kg)
- 2
- Amount of substance (mol)
- 1
Chemistry results
| Molality (mol/kg) | 2 |
| Amount of substance (mol) | 1 |
formula-map diagram
- Molality (mol/kg)
- 2
- Amount of substance (mol)
- 1
Formula breakdown
Formula
b = n(solute) ÷ solvent mass (kg)= 2
Note
Simplified model: these results assume ideal behaviour (ideal gases, dilute solutions, complete reactions) and standard textbook constants. Real laboratory values vary with temperature, pressure, purity and activity coefficients. Do not rely on this for safety-critical or analytical work.
More in Chemistry
See all →Frequently asked questions
What is molality and how does it differ from molarity?+
Molality (m) is moles of solute per kilogram of solvent (not solution): m = moles of solute / kg of solvent. Unlike molarity, it doesn't depend on volume, so it doesn't change with temperature, making it the preferred unit for precise physical chemistry calculations like freezing-point depression.
Why is molality preferred over molarity for some calculations?+
Because molality is based on mass, not volume, it remains constant even as temperature changes and the solution expands or contracts, whereas molarity shifts slightly with temperature. This makes molality the standard choice for colligative property calculations like boiling-point elevation and freezing-point depression.
How do you calculate molality if you're given the mass of solute and solvent?+
First convert the solute's mass to moles using its molar mass, then divide by the solvent's mass converted to kilograms: molality = moles of solute / kg of solvent. Be careful to use only the solvent's mass, not the total solution mass.
Can molality and molarity give very different values for the same solution?+
For dilute aqueous solutions they're numerically close since water's density is near 1 kg/L, but for concentrated solutions or solvents with a density far from water's, molality and molarity can diverge noticeably. Always check which one a formula or problem specifically requires.
What's a common mistake when calculating molality?+
Using the mass of the entire solution (solute plus solvent) in the denominator instead of just the solvent's mass is the most frequent error, since that would actually describe a mass-fraction-based concentration, not true molality.