Question 1
How many molecules are in 0.10 mol of any molecular substance?
Need a hint for Question 1?
Use the relationships above and check particle ratios and units.
Check Question 1
0.10 × 6.02 × 10²³ = 6.02 × 10²² molecules.
STUDENT SPACE · TOPIC 1
Moles, mass and particles
Convert between mass, amount in moles and number of particles.
The essentials
- One mole contains 6.02 × 10²³ specified particles for CIE calculations.
- Name the particles: atoms, molecules, ions or formula units.
- 12 g carbon and 24 g magnesium each contain 1 mol of atoms.
- Molar mass M is the mass of one mole, in g/mol.
Key vocabulary
| English | Chinese |
|---|---|
| mole | 摩尔 |
| molar mass | 摩尔质量 |
| Avogadro constant | 阿伏伽德罗常数 |
Quick practice
Try each question before opening its hint or answer. Use paper for calculations and diagrams.
Question 2
Calculate the mass of 0.20 mol CO₂. M(CO₂) = 44 g/mol.
Need a hint for Question 2?
Use mass = moles × molar mass.
Check Question 2
m = nM = 0.20 × 44 = 8.8 g.
Question 3
A 6.0 g sample contains 0.10 mol of molecules. Find its molar mass.
Need a hint for Question 3?
Rearrange amount = mass / molar mass.
Check Question 3
M = m/n = 6.0/0.10 = 60 g/mol.
Use Lesson 1 in your worksheet for written practice. Your teacher will discuss those answers in class.
PREDICT · TRY · EXPLAIN · 3–5 MINUTES
From mass to moles to mass
Predict the product mass. Reveal each step and explain why the equation ratio is not a mass ratio.
2Mg + O₂ → 2MgO
Assume excess oxygen and complete reaction. M(Mg) = 24 g mol⁻¹; M(MgO) = 40 g mol⁻¹.
- Step 1 · Convert the known mass into moles.
- Step 2 · Use the balanced equation to find product moles.
- Step 3 · Convert product moles into mass.
Explain: why must we divide by one molar mass and multiply by another? Display values are rounded; calculations use full precision.