Converting grams to moles
moles = mass ÷ molar mass.
The common mistake
Multiplying by the molar mass instead of dividing, or using the atomic number.
Instead: Add up relative atomic masses to get molar mass (g/mol), then divide the mass in grams by it.
Worked example with Guide me
How many moles are in 36 g of water (H₂O)?
- Sugar · Molar mass of H₂O?Student · 2(1) + 16 = 18 g/mol.
- Sugar · Divide mass by molar mass.Student · 36 ÷ 18 = 2.
Answer: 2 mol
Try 3 practice questions
1. Moles in 88 g of CO₂ (C = 12, O = 16)?
Show answer
2 mol
2. Mass of 0.5 mol of NaCl (58.5 g/mol)?
Show answer
29.25 g
3. Molar mass of CH₄?
Show answer
16 g/mol
Quick answers
- What is the most common mistake with converting grams to moles?
- Multiplying by the molar mass instead of dividing, or using the atomic number.
- How do I get converting grams to moles right?
- Add up relative atomic masses to get molar mass (g/mol), then divide the mass in grams by it.
- Can you show a worked example?
- How many moles are in 36 g of water (H₂O)? 2 mol
Related concepts
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