Mole Conversions: Grams, Moles and Particles Step by Step
Convert between grams, moles and particles using molar mass and Avogadro's number, with two worked examples and a common unit mistake.
The mole map
- Grams ↔ moles · molar mass
- Moles ↔ particles · 6.02 × 10²³
- Moles ↔ gas liters · 22.4 L at STP
Every conversion goes through moles.
Molar mass first
- Add the atomic masses in the formula
- H₂O = 2(1.01) + 16.00 = 18.02
- Units: grams per mole
Find molar mass before anything else.
Example 1
How many moles are in 36.04 g of H₂O?
- Molar mass of H₂O is 18.02 g/mol.
- moles = 36.04 / 18.02
2.00 mol
Example 2
How many molecules are in 2.00 mol of H₂O?
- Use Avogadro's number: 6.02 × 10²³ per mole.
- 2.00 × 6.02 × 10²³
1.20 × 10²⁴ molecules
Common mistake
moles = grams × molar mass
Divide: moles = grams ÷ molar mass.
Check units: g ÷ (g/mol) leaves mol.
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