Library / Foundations: Chemistry / FCH-03
Foundations: Chemistry
Moles from mass
Convert the mass of a substance into the amount in moles.
- Ref
- FCH-03
- Rev
- v1
- Field
- Foundations: Chemistry
- Result
- n [mol]
n is in mol, m in g and Mr is the relative formula mass (molar mass in g/mol).
Chemical reactions work by counting particles, and the mole is the counting unit. Dividing mass by molar mass gives the count.
Calculator
mol
g
g/mol
- Number of particles0.6022 10²³
- Amount in mmol100 mmol
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.
Amount (mol) current value 0.1 mol
mMassKey driver
4.17e-441.7
MrRelative formula mass
0.00482.4
- 24 g of magnesium is exactly 1 mole of atoms.
- Rearranged: m = n × Mr, which gives the mass needed for a chosen amount.
Chart data as tables
Ranked variables
| Variable | Typical range | Lowest result | Highest result | Swing (mol) | Local step | Change in result |
|---|---|---|---|---|---|---|
| m Mass | 0.01 to 1,000 g | 4.167e-4 | 41.67 | 41.67 | +10% | +10 % |
| Mr Relative formula mass | 1 to 500 g/mol | 0.0048 | 2.4 | 2.395 | +10% | −9.09 % |
Sweep of Mass
| Mass (g) | Amount (mol) |
|---|---|
| 0.01 | 4.167e-4 |
| 0.04217 | 0.001757 |
| 0.1778 | 0.007409 |
| 0.7499 | 0.03125 |
| 3.162 | 0.1318 |
| 13.34 | 0.5556 |
| 56.23 | 2.343 |
| 237.1 | 9.881 |
| 1,000 | 41.67 |
Sweep one variable
Amount (mol)Hover, touch, or use the arrow keys on the chart
Variables and how each one contributes
n
Amount
What the equation gives you. Everything else feeds it.
m
Mass
Mass of the substance. Directly proportional.
Mr
Relative formula mass
Molar mass of the substance (Mg = 24). Inversely proportional.
Worked example with the values above
- n = m / Mr = 2.4 g / 24 g/mol.
- Divide: 0.1.
- n = 0.1 mol.
Assumptions and limits
- Pure sample.
- Correct formula used for Mr.
Common mistakes
- Using the formula mass of the wrong species (atoms versus molecules).
- Mixing kg and g.
Statistics and uncertainty
Balance precision of ±0.01 g on a 2.40 g sample is about 0.4%, which carries straight into the moles.
Where it is used
- Weighing out reagents.
- Starting point for yield, gas volume and concentration problems.
Maths you need
- Relative formula mass: Mr
- Division: g per g/mol