Library / Chemical / CHE-01
Chemical
Amount and concentration
Moles and molar concentration from mass, molar mass and volume.
- Ref
- CHE-01
- Rev
- v1
- Field
- Chemical
- Result
- C [mol/L]
nA amount in mol, mA mass, MA molar mass, CA concentration and V the solution volume. Mass in grams and molar mass in g/mol give moles; volume in litres gives mol/L.
Chemists count molecules in moles. Dividing a mass by the molar mass gives the number of moles, and dividing that by the volume gives the concentration.
Calculator
- Amount n0.2002 mol
- Concentration in mol/m³400.4 mol/m³
What drives the result
Each variable is moved across its typical range while the others stay at the values above. The longest bar is the key driver.
- 1 mol/L equals 1000 mol/m³, a conversion that matters in SI reactor calculations.
- Mixing mass and molar units (kg with g/mol) is the commonest error.
- Volume changes on dissolving; for precise work use the final solution volume.
Chart data as tables
Ranked variables
| Variable | Typical range | Lowest result | Highest result | Swing (mol/L) | Local step | Change in result |
|---|---|---|---|---|---|---|
| m Mass of solute | 0.1 to 1,000 g | 0.003422 | 34.22 | 34.22 | +10% | +10 % |
| M Molar mass | 1 to 500 g/mol | 0.0468 | 23.4 | 23.35 | +10% | −9.09 % |
| V Volume | 0.01 to 100 L | 0.002002 | 20.02 | 20.02 | +10% | −9.09 % |
Sweep of Volume
| Volume (L) | Concentration (mol/L) |
|---|---|
| 0.01 | 20.02 |
| 0.03162 | 6.331 |
| 0.1 | 2.002 |
| 0.3162 | 0.6331 |
| 1 | 0.2002 |
| 3.162 | 0.06331 |
| 10 | 0.02002 |
| 31.62 | 0.006331 |
| 100 | 0.002002 |
Sweep one variable
Variables and how each one contributes
Concentration
What the equation gives you. Everything else feeds it.
Mass of solute
Mass dissolved. Directly proportional.
Molar mass
Mass of one mole (NaCl 58.44). Inversely proportional.
Volume
Volume of the solution. Inversely proportional.
Worked example with the values above
- Amount: n = m/M = 11.7 g / 58.44 g/mol = 0.2002 mol.
- Divide by volume: 0.2002 mol / 0.5 L.
- C = 0.4004 mol/L.
Assumptions and limits
- Pure solute and a known molar mass.
- Volume is the final solution volume.
- Consistent units throughout.
Common mistakes
- Using the volume of the solvent instead of the solution.
- Mixing kg and g.
- Using the wrong molar mass (hydrates).
Statistics and uncertainty
A balance accurate to ±0.01 g on 11.7 g gives 0.1% error; the volumetric flask is usually the larger error, around ±0.2%. They combine as δC/C ≈ √[(δm/m)² + (δV/V)²].
Where it is used
- Preparing electrolytes and reagents.
- Reactor feed concentrations.
- Corrosion and decontamination solutions.
Maths you need
- Moles: a counting unit for molecules
- Units: g, L and mol