Aqueous Dimethylamine: wt%, Molarity and Molality Explained
2026-11-11
Aqueous Dimethylamine: wt%, Molarity and Molality Explained
China Amines Co., Limited
A purchasing specification may describe aqueous dimethylamine in weight percent. A laboratory calculation may require mol/L. A thermodynamic reference may use mol/kg of water.
These expressions describe different quantities. Changing the unit label without changing the calculation can turn a familiar product into a surprisingly unfamiliar spreadsheet.
For technical discussions, the essential question is: What appears in the denominator—solution mass, solution volume or solvent mass?
1. Weight percent uses total solution mass
Mass fraction describes the mass of a constituent divided by the total mixture mass. Expressing that fraction as a percentage gives the familiar mass-percentage basis. goldbook.iupac.org
For a hypothetical solution containing exactly 40.0% DMA by mass, each 1,000 g of solution contains 400 g of DMA.
That statement does not specify the solution’s volume. It also does not establish that every remaining gram is water unless a binary DMA–water composition is assumed.
2. Convert DMA mass into amount of substance
NIST reports a molecular weight of approximately 45.08 for dimethylamine, corresponding to a molar mass of approximately 45.08 g/mol. webbook.nist.gov
For the example:
Amount of DMA = 400 g ÷ 45.08 g/mol ≈ 8.87 mol
The solution therefore contains approximately 8.87 mol of DMA per kilogram of solution.
This is useful composition information, but it is neither molarity nor molality.
3. Molarity requires solution volume
Molarity, more formally amount concentration, expresses amount of substance per solution volume. A common unit is mol/L. NIST
To convert a mass-percentage specification into mol/L, the solution density is needed.
When density ρ is expressed in kg/L, DMA mass fraction w is dimensionless, and molar mass M is in g/mol:
DMA amount concentration = 1,000 × ρ × w ÷ M
Use density appropriate to the composition and stated temperature. Do not assume that one kilogram of aqueous DMA occupies one litre.
4. Molality uses solvent mass
IUPAC defines molality as the amount of solute divided by solvent mass. Its usual unit is mol/kg of solvent. goldbook.iupac.org
Now assume the hypothetical 40.0% solution contains only DMA and water. Its 1,000 g total mass comprises:
- 400 g DMA.
- 600 g water.
- Approximately 8.87 mol DMA.
The calculated molality is therefore:
8.87 mol ÷ 0.600 kg water ≈ 14.8 mol/kg water
The difference from 8.87 mol/kg solution comes entirely from changing the denominator.
5. Keep the quantities clearly labelled
| Expression | Meaning in the hypothetical example |
|---|---|
| 40.0 wt% DMA | 40.0 g DMA per 100 g solution |
| 8.87 mol/kg solution | DMA amount per total solution mass |
| 14.8 mol/kg water | Molality, assuming only DMA and water |
| mol/L solution | Requires suitable density or volume information |
These calculated values are illustrative, not China Amines specifications. They describe analytical composition rather than chemical activity or reaction performance.
When transferring a calculation between purchasing, laboratory and production records, preserve the concentration basis, temperature where relevant, and underlying assumptions.
About China Amines
China Amines Co., Limited welcomes inquiries for aqueous dimethylamine used in chemical manufacturing. Please provide your required concentration and reporting basis, application, quantity, destination and technical-documentation needs.
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References
- IUPAC Gold Book — Mass Fraction
- NIST Chemistry WebBook — Dimethylamine
- NIST — Guide to the SI, Chapter 8
- IUPAC Gold Book — Molality