Chemistry and laboratory
Molarity calculator and solution preparation
Mass to weigh for a volume and molar concentration, or the molarity of a solution you made, with g/L, % w/v and ppm equivalents.
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Result
- Mass to weigh
- 2.92 g
- Amount of solute
- 50.0 mmol
- Molar mass used
- NaCl, 58.44 g/mol
Working
- n = c × V = 0.1 mol/L × 0.5 L = 0.05 mol
- m = n × M = 0.05 mol × 58.44 g/mol = 2.922 g
| Unit | Value |
|---|---|
| mol/L (M) | 0.100 |
| mmol/L (mM) | 100 |
| g/L | 5.84 |
| mg/mL | 5.84 |
| % w/v (g/100 mL) | 0.584 |
| ppm (mg/L) | 5840 |
- Dissolve the solute and make up to the final volume in a volumetric flask: the volume is of the finished solution, not of the solvent added.
- ppm here means mg per litre of a dilute aqueous solution (density taken as 1 g/mL). For hydrates, enter the hydrate formula you weigh, such as CuSO4·5H2O.
- Rounded to 3 significant figures.
Method and limits
Choose what to calculate; that field is filled in for you and the other two are used. The answer updates as you type.
c = n ÷ V = m ÷ (M × V) m = c × V × M ÷ purity
c is the molar concentration in mol/L (M), V the final volume of solution in litres, m the mass in grams and M the molar mass from CIAAW 2024 atomic weights. The purity divides the mass to weigh: a 98 % reagent needs 1/0.98 times as much.
Equivalent units
- g/L = c × M; mg/mL is numerically the same.
- % w/v = grams per 100 mL = (g/L) ÷ 10.
- ppm here is mg per litre of a dilute aqueous solution (1 ppm ≈ 1 mg/L, which assumes a density of 1 g/mL). For concentrated solutions, mass-based ppm needs the density.
Limits
V is the volume of the finished solution, not of the water added: dissolve, then make up to the mark in a volumetric flask. Molarity changes slightly with temperature because the volume does. Answers keep the significant figures of the least precise number you enter (at least 3, at most 6); counts and coefficients are exact and do not limit precision.
Worked example
500 mL of 0.100 M NaCl (58.44 g/mol): n = 0.100 mol/L × 0.500 L = 0.0500 mol; m = 0.0500 mol × 58.44 g/mol = 2.92 g. The solution is 5.84 g/L, 0.584 % w/v.
References
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