Redox chemistry worksheet for Form 5 students, focusing on identifying oxidized/reduced elements and oxidizing/reducing agents in various chemical reactions.

Let's solve each of the redox (oxidation-reduction) reactions step by step. We need to:

1. Determine oxidation states of elements before and after the reaction.
2. Identify which element is oxidized (loses electrons, increase in oxidation state).
3. Identify which element is reduced (gains electrons, decrease in oxidation state).
4. The reducing agent is the substance that causes reduction (it itself gets oxidized).
5. The oxidizing agent is the substance that causes oxidation (it itself gets reduced).

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1) 2Sr + O₂ → 2SrO

- Sr: starts at 0 (elemental), ends at +2 in SrO
- O: starts at 0 (O₂), ends at -2 in SrO

✔ Oxidized: Sr (0 → +2)
✔ Reduced: O (0 → -2)
✔ Reducing Agent: Sr (gets oxidized)
✔ Oxidizing Agent: O₂ (gets reduced)

| Reduced Element | Oxidized Element | Reducing Agent | Oxidizing Agent |
|------------------|-------------------|----------------|------------------|
| O | Sr | Sr | O₂ |

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2) 2Li + S → Li₂S

- Li: 0 → +1
- S: 0 → -2

✔ Oxidized: Li
✔ Reduced: S
✔ Reducing Agent: Li
✔ Oxidizing Agent: S

| Reduced Element | Oxidized Element | Reducing Agent | Oxidizing Agent |
|------------------|-------------------|----------------|------------------|
| S | Li | Li | S |

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3) 2Cs + Br₂ → 2CsBr

- Cs: 0 → +1
- Br: 0 → -1

✔ Oxidized: Cs
✔ Reduced: Br
✔ Reducing Agent: Cs
✔ Oxidizing Agent: Br₂

| Reduced Element | Oxidized Element | Reducing Agent | Oxidizing Agent |
|------------------|-------------------|----------------|------------------|
| Br | Cs | Cs | Br₂ |

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4) 3Mg + N₂ → Mg₃N₂

- Mg: 0 → +2
- N: 0 → -3

✔ Oxidized: Mg
✔ Reduced: N
✔ Reducing Agent: Mg
✔ Oxidizing Agent: N₂

| Reduced Element | Oxidized Element | Reducing Agent | Oxidizing Agent |
|------------------|-------------------|----------------|------------------|
| N | Mg | Mg | N₂ |

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5) 4Fe + 3O₂ → 2Fe₂O₃

- Fe: 0 → +3
- O: 0 → -2

✔ Oxidized: Fe
✔ Reduced: O
✔ Reducing Agent: Fe
✔ Oxidizing Agent: O₂

| Reduced Element | Oxidized Element | Reducing Agent | Oxidizing Agent |
|------------------|-------------------|----------------|------------------|
| O | Fe | Fe | O₂ |

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6) Cl₂ + 2NaBr → 2NaCl + Br₂

This is a displacement reaction.

- Cl₂: 0 → -1 in NaCl (reduced)
- Br⁻ in NaBr: -1 → 0 in Br₂ (oxidized)
- Na⁺ remains +1 throughout

So:
- Cl₂ gains electrons → reduced
- Br⁻ loses electrons → oxidized

✔ Oxidized: Br (from Br⁻ to Br₂)
✔ Reduced: Cl (from Cl₂ to Cl⁻)
✔ Reducing Agent: NaBr (provides Br⁻, which gets oxidized)
✔ Oxidizing Agent: Cl₂ (gets reduced)

| Reduced Element | Oxidized Element | Reducing Agent | Oxidizing Agent |
|------------------|-------------------|----------------|------------------|
| Cl | Br | NaBr | Cl₂ |

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7) Si + 2F₂ → SiF₄

- Si: 0 → +4
- F: 0 → -1

✔ Oxidized: Si
✔ Reduced: F
✔ Reducing Agent: Si
✔ Oxidizing Agent: F₂

| Reduced Element | Oxidized Element | Reducing Agent | Oxidizing Agent |
|------------------|-------------------|----------------|------------------|
| F | Si | Si | F₂ |

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8) 2Ca + O₂ → 2CaO

- Ca: 0 → +2
- O: 0 → -2

✔ Oxidized: Ca
✔ Reduced: O
✔ Reducing Agent: Ca
✔ Oxidizing Agent: O₂

| Reduced Element | Oxidized Element | Reducing Agent | Oxidizing Agent |
|------------------|-------------------|----------------|------------------|
| O | Ca | Ca | O₂ |

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9) Mg + 2HCl → MgCl₂ + H₂

- Mg: 0 → +2
- H: +1 in HCl → 0 in H₂
- Cl: -1 (no change)

So:
- Mg loses electrons → oxidized
- H⁺ gains electrons → reduced

✔ Oxidized: Mg
✔ Reduced: H (from H⁺ to H₂)
✔ Reducing Agent: Mg
✔ Oxidizing Agent: HCl (provides H⁺, which gets reduced)

| Reduced Element | Oxidized Element | Reducing Agent | Oxidizing Agent |
|------------------|-------------------|----------------|------------------|
| H | Mg | Mg | HCl |

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10) 2Na + 2H₂O → 2NaOH + H₂

- Na: 0 → +1
- H in H₂O: +1 → 0 in H₂ (reduced)
- O: -2 (no change)
- NaOH: Na⁺, O²⁻, H⁺

So:
- Na → Na⁺ → oxidized
- H⁺ from water → H₂ → reduced

✔ Oxidized: Na
✔ Reduced: H (in H₂O)
✔ Reducing Agent: Na
✔ Oxidizing Agent: H₂O (provides H⁺, which gets reduced)

| Reduced Element | Oxidized Element | Reducing Agent | Oxidizing Agent |
|------------------|-------------------|----------------|------------------|
| H | Na | Na | H₂O |

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✔ Final Answers Summary:

| Reaction | Reduced Element | Oxidized Element | Reducing Agent | Oxidizing Agent |
|--------|------------------|-------------------|----------------|------------------|
| 1 | O | Sr | Sr | O₂ |
| 2 | S | Li | Li | S |
| 3 | Br | Cs | Cs | Br₂ |
| 4 | N | Mg | Mg | N₂ |
| 5 | O | Fe | Fe | O₂ |
| 6 | Cl | Br | NaBr | Cl₂ |
| 7 | F | Si | Si | F₂ |
| 8 | O | Ca | Ca | O₂ |
| 9 | H | Mg | Mg | HCl |
|10 | H | Na | Na | H₂O |

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🔍 Key Concepts Recap:

- Oxidation: Loss of electrons, increase in oxidation number.
- Reduction: Gain of electrons, decrease in oxidation number.
- Reducing Agent: Gets oxidized → causes reduction.
- Oxidizing Agent: Gets reduced → causes oxidation.

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