All calculatorsMolality (m) Calculator
Compute molality m in mol·kg⁻¹ from solute amount and solvent mass. Supports auto molar mass from a chemical formula, step-by-step working, and an optional mini chart linking moles solute ↔ kg solvent ↔ molality.
Background
Molality is temperature-independent and defined as m = nsolute / kg solvent. Get moles (n) from mass using the molar mass M, or enter moles directly. Solvent mass must be in kilograms.
How to use this calculator
- Solute amount: Enter moles directly, or enter mass and molar mass (M). A formula can auto-fill M.
- Solvent mass: Enter in g or kg; we convert to kg.
- Molality: m = nsolute / kg solvent (mol per kg of solvent).
- Advanced: If you know solution mass and wt% solute, enable Advanced to compute kg solvent automatically.
Formula & Equation Used
Definition: m = nsolute / kg solvent
From mass of solute: nsolute = msolute / M
Advanced (mass %): msolute = (%w/w / 100) · msolution, then msolvent = msolution − msolute
Examples
10.0 g NaCl in 100.0 g water
M(NaCl)=58.44 g/mol → n = 10.0 / 58.44 = 0.171 mol; solvent = 0.1000 kg → m = 0.171 / 0.1000 = 1.71 m.
0.50 mol KCl in 0.500 kg water
m = 0.50 / 0.500 = 1.00 m.
18 g glucose (C₆H₁₂O₆) in 0.200 kg water
M≈180.16 g/mol → n = 18 / 180.16 = 0.0999 mol → m = 0.0999 / 0.200 = 0.499 m.
Frequently Asked Questions
Q: Molality vs Molarity?
Molality is moles per kilogram of solvent (temperature-independent). Molarity is moles per liter of solution (temperature-dependent).
Q: Can I use density?
Not needed for molality—only mass of solvent matters. For molarity, volume (and often density) is required.
