Mole calculations worksheet|KS4 Chemistry|Teachit - Free Printable

Absolutely! Let's solve both Task 1 and Task 2 step by step. The key concept here is the relationship between moles, mass (in grams), and molar mass (atomic mass in g/mol).

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## 🔑 Key Formula:

> Mass (g) = Moles × Molar Mass (g/mol)
> Moles = Mass (g) ÷ Molar Mass (g/mol)

You’ll need to look up the atomic masses from the periodic table. Here are the standard atomic masses we’ll use (rounded to 1 decimal place for simplicity, as commonly used in such exercises):

| Element | Symbol | Atomic Mass (g/mol) |
|---------|--------|---------------------|
| Carbon | C | 12.0 |
| Sodium | Na | 23.0 |
| Magnesium | Mg | 24.3 |
| Gold | Au | 197.0 |
| Silicon | Si | 28.1 |
| Bromine | Br | 79.9 |
| Phosphorus | P | 31.0 |
| Iron | Fe | 55.8 |
| Neon | Ne | 20.2 |
| Copper | Cu | 63.5 |
| Silver | Ag | 107.9 |
| Helium | He | 4.0 |
| Lithium | Li | 6.9 |
| Hydrogen | H | 1.0 |
| Calcium | Ca | 40.1 |

*(Note: Some values may vary slightly depending on the periodic table used — these are common textbook values.)*

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# ✔ TASK 1: Find the mass (in grams) of given moles of atoms

Use: Mass = Moles × Molar Mass

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a) 5 moles of carbon (C) atoms

Mass = 5 mol × 12.0 g/mol = 60.0 g

b) 3 moles of sodium (Na) atoms

Mass = 3 mol × 23.0 g/mol = 69.0 g

c) 2.5 moles of magnesium (Mg) atoms

Mass = 2.5 mol × 24.3 g/mol = 60.75 g → 60.8 g (rounded to 1 decimal)

d) 6 moles of gold (Au) atoms

Mass = 6 mol × 197.0 g/mol = 1182.0 g

e) 0.8 moles of silicon (Si) atoms

Mass = 0.8 mol × 28.1 g/mol = 22.48 g → 22.5 g

f) 0.5 moles of bromine (Br) atoms

Mass = 0.5 mol × 79.9 g/mol = 39.95 g → 40.0 g

g) 1.5 moles of phosphorus (P) atoms

Mass = 1.5 mol × 31.0 g/mol = 46.5 g

h) 2 moles of iron (Fe) atoms

Mass = 2 mol × 55.8 g/mol = 111.6 g

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✔ Task 1 Answers:

a) 60.0 g
b) 69.0 g
c) 60.8 g
d) 1182.0 g
e) 22.5 g
f) 40.0 g
g) 46.5 g
h) 111.6 g

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# ✔ TASK 2: Find how many moles are in given masses

Use: Moles = Mass ÷ Molar Mass

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a) 48 g of magnesium (Mg) atoms

Moles = 48 g ÷ 24.3 g/mol ≈ 1.975 mol → 1.98 mol (rounded to 2 decimals)

b) 80 g of neon (Ne) atoms

Moles = 80 g ÷ 20.2 g/mol ≈ 3.960 mol → 3.96 mol

c) 128 g of copper (Cu) atoms

Moles = 128 g ÷ 63.5 g/mol ≈ 2.016 mol → 2.02 mol

d) 324 g of silver (Ag) atoms

Moles = 324 g ÷ 107.9 g/mol ≈ 3.003 mol → 3.00 mol

e) 14 g of helium (He) atoms

Moles = 14 g ÷ 4.0 g/mol = 3.50 mol

f) 3.5 g of lithium (Li) atoms

Moles = 3.5 g ÷ 6.9 g/mol ≈ 0.507 mol → 0.51 mol

g) 0.2 g of hydrogen (H) atoms

Moles = 0.2 g ÷ 1.0 g/mol = 0.20 mol

h) 100 g of calcium (Ca) atoms

Moles = 100 g ÷ 40.1 g/mol ≈ 2.494 mol → 2.49 mol

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✔ Task 2 Answers:

a) 1.98 moles
b) 3.96 moles
c) 2.02 moles
d) 3.00 moles
e) 3.50 moles
f) 0.51 moles
g) 0.20 moles
h) 2.49 moles

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## 🧠 Summary:

- To find mass: Multiply moles by molar mass.
- To find moles: Divide mass by molar mass.
- Always use the atomic mass from the periodic table — it’s essential!
- Round answers appropriately (usually to 2 decimal places unless specified).

Let me know if you’d like to see the calculations written out with units or want to check your own answers! 😊