Number of Moles
Converts a mass of substance into moles.
n = \dfrac{m}{M}
1What it means
A mole is a fixed count of particles (6.022 × 10²³). Dividing the given mass by the molar mass tells you how many moles you have.
2Variables
| Symbol | Meaning |
|---|---|
| n | Number of moles (mol) |
| m | Given mass (g) |
| M | Molar mass (g/mol) |
3Worked examples
Example 1 Worked solution
Q. How many moles are in 36 g of water (M = 18 g/mol)?
- n = m / M = 36 / 18.
✓ n = 2 mol
4Where it's used
- ✦Balancing reactions and stoichiometry.
- ✦Preparing solutions of known concentration.
5Tips & common mistakes
- !Molar mass = sum of atomic masses in the formula.
- !Mass must be in grams to match g/mol.