Worksheet on chemical formulae and relative formula mass, including tasks to interpret formulae and calculate masses.

Let’s work through this step by step.

---

Task 1: What do these formulae mean? Complete the table below.

We need to break down each chemical formula and list how many of each atom it contains.

Remember:
- A subscript (small number after an element) tells you how many atoms of that element are in the molecule.
- If there’s a bracket with a subscript outside, like (NO₃)₂, multiply everything inside the bracket by that number.
- No subscript means 1 atom.

Let’s go one by one:

1. H₂ → Already done: 2 hydrogen atoms
2. NaCl → Sodium chloride → 1 sodium atom, 1 chlorine atom
3. Al₂O₃ → Aluminum oxide → 2 aluminum atoms, 3 oxygen atoms
4. CaCO₃ → Calcium carbonate → 1 calcium, 1 carbon, 3 oxygen
5. K₂CO₃ → Potassium carbonate → 2 potassium, 1 carbon, 3 oxygen
6. NaHCO₃ → Sodium bicarbonate → 1 sodium, 1 hydrogen, 1 carbon, 3 oxygen
7. H₂SO₄ → Sulfuric acid → 2 hydrogen, 1 sulfur, 4 oxygen
8. Ca(NO₃)₂ → Calcium nitrate → 1 calcium, then (NO₃)₂ means 2 × N = 2 nitrogen, and 2 × 3 O = 6 oxygen → So: 1 Ca, 2 N, 6 O
9. (NH₄)₂SO₄ → Ammonium sulfate → (NH₄)₂ means 2 × N = 2 nitrogen, 2 × 4 H = 8 hydrogen; SO₄ is 1 sulfur, 4 oxygen → Total: 2 N, 8 H, 1 S, 4 O
10. CH₃CH₂OH → Ethanol → This can be rewritten as C₂H₆O (since CH₃ + CH₂ + OH = 2C, 3+2+1=6H, 1O) → So: 2 carbon, 6 hydrogen, 1 oxygen

✔ Task 1 completed.

---

Task 2: Calculate relative formula mass (Mᵣ) and mass of 1 mole

Relative formula mass (Mᵣ) = sum of all atomic masses in the formula.

Mass of 1 mole = same number as Mᵣ, but in grams (g/mol).

We’re given atomic masses at the bottom:

> H = 1, C = 12, N = 14, O = 16, Na = 23, Al = 27, S = 32, Cl = 35.5, K = 39, Ca = 40

Let’s calculate each:

1. H₂ → 2 × 1 = 2 → Mass of 1 mole = 2 g

2. NaCl → 23 + 35.5 = 58.5 → 58.5 g

3. Al₂O₃ → (2 × 27) + (3 × 16) = 54 + 48 = 102 → 102 g

4. CaCO₃ → 40 + 12 + (3 × 16) = 40 + 12 + 48 = 100 → 100 g

5. K₂CO₃ → (2 × 39) + 12 + (3 × 16) = 78 + 12 + 48 = 138 → 138 g

6. NaHCO₃ → 23 + 1 + 12 + (3 × 16) = 23 + 1 + 12 + 48 = 84 → 84 g

7. H₂SO₄ → (2 × 1) + 32 + (4 × 16) = 2 + 32 + 64 = 98 → 98 g

8. Ca(NO₃)₂ → 40 + [2 × (14 + 3×16)] = 40 + [2 × (14 + 48)] = 40 + [2 × 62] = 40 + 124 = 164 → 164 g

9. (NH₄)₂SO₄ → [2 × (14 + 4×1)] + 32 + (4 × 16) = [2 × (14 + 4)] + 32 + 64 = [2 × 18] + 96 = 36 + 96 = 132 → 132 g

10. CH₃CH₂OH → As we said, C₂H₆O → (2 × 12) + (6 × 1) + 16 = 24 + 6 + 16 = 46 → 46 g

✔ All calculations checked — they match standard values.

---

Final Answer:

Task 1 Table:

| Formula | The atoms it contains |
|-------------|------------------------------------------------|
| H₂ | 2 hydrogen atoms |
| NaCl | 1 sodium atom, 1 chlorine atom |
| Al₂O₃ | 2 aluminum atoms, 3 oxygen atoms |
| CaCO₃ | 1 calcium atom, 1 carbon atom, 3 oxygen atoms |
| K₂CO₃ | 2 potassium atoms, 1 carbon atom, 3 oxygen atoms |
| NaHCO₃ | 1 sodium atom, 1 hydrogen atom, 1 carbon atom, 3 oxygen atoms |
| H₂SO₄ | 2 hydrogen atoms, 1 sulfur atom, 4 oxygen atoms |
| Ca(NO₃)₂ | 1 calcium atom, 2 nitrogen atoms, 6 oxygen atoms |
| (NH₄)₂SO₄ | 2 nitrogen atoms, 8 hydrogen atoms, 1 sulfur atom, 4 oxygen atoms |
| CH₃CH₂OH | 2 carbon atoms, 6 hydrogen atoms, 1 oxygen atom |

Task 2 Table:

| Formula | Relative formula mass (Mᵣ) | Mass of 1 mole |
|-------------|-----------------------------|----------------|
| H₂ | 2 | 2 g |
| NaCl | 58.5 | 58.5 g |
| Al₂O₃ | 102 | 102 g |
| CaCO₃ | 100 | 100 g |
| K₂CO₃ | 138 | 138 g |
| NaHCO₃ | 84 | 84 g |
| H₂SO₄ | 98 | 98 g |
| Ca(NO₃)₂ | 164 | 164 g |
| (NH₄)₂SO₄ | 132 | 132 g |
| CH₃CH₂OH | 46 | 46 g |