Topic: Identification of Ions and Gases
Lesson 1: Tests for Anions
| Section | Details |
|---|---|
| Objective | – Describe tests to identify anions (carbonate, chloride, bromide, iodide, nitrate, sulfate, sulfite). |
| Activities | – Starter (5 mins): Show a mixture of sand and salt and ask: “How can we identify the ions in this sample?”- Main (25 mins): 1. Explain the tests for anions: – Carbonate (CO₃²⁻): React with dilute acid; test for CO₂ using limewater. – Chloride (Cl⁻), Bromide (Br⁻), Iodide (I⁻): Acidify with dilute nitric acid, then add silver nitrate. – Nitrate (NO₃⁻): Reduction with aluminum foil and sodium hydroxide; test for ammonia gas. – Sulfate (SO₄²⁻): Acidify with nitric acid, then add barium nitrate. – Sulfite (SO₃²⁻): React with potassium manganate(VII); observe purple color fading. 2. Demonstrate or show video examples of these tests.- Plenary (10 mins): Students complete a table matching anions to their tests and observations. |
| Resources | Test tubes, reagents (acids, silver nitrate, limewater, barium nitrate), worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write equations for the reactions involved in identifying carbonate, sulfate, and nitrate ions. |
| Assessment | Worksheet: Identify anions from test observations. |
| Past Paper Practice | IGCSE Chemistry 0620/41/M/J/20 Q5(a). |
Lesson 2: Tests for Cations
| Section | Details |
|---|---|
| Objective | – Describe tests using sodium hydroxide and ammonia to identify cations. |
| Activities | – Starter (5 mins): Show images of different precipitates and ask: “What do these colors indicate?”- Main (25 mins): 1. Explain reactions of cations with NaOHNaOH and NH3NH₃: – Al³⁺: White precipitate dissolves in excess NaOHNaOH. – NH₄⁺: Ammonia gas evolved. – Ca²⁺: White precipitate. – Cu²⁺: Blue precipitate (deep blue in excess NH3NH₃). – Fe²⁺: Green precipitate. – Fe³⁺: Brown precipitate. – Zn²⁺: White precipitate dissolves in excess NaOHNaOH or NH3NH₃. 2. Demonstrate tests or use a video.- Plenary (10 mins): Students complete a table summarizing test results. |
| Resources | Sodium hydroxide, ammonia, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write equations for reactions of NaOHNaOH with aluminum and copper ions. |
| Assessment | Worksheet: Identify cations based on test observations. |
| Past Paper Practice | IGCSE Chemistry 0620/41/O/N/21 Q5(b). |
Lesson 3: Tests for Gases
| Section | Details |
|---|---|
| Objective | – Describe tests for identifying gases (ammonia, carbon dioxide, chlorine, hydrogen, oxygen, sulfur dioxide). |
| Activities | – Starter (5 mins): Show images of different gases being tested and ask: “How do we identify gases in experiments?”- Main (25 mins): 1. Discuss gas tests: – Ammonia (NH₃): Turns damp red litmus paper blue. – Carbon dioxide (CO₂): Turns limewater milky. – Chlorine (Cl₂): Bleaches damp litmus paper. – Hydrogen (H₂): Pops with a lighted splint. – Oxygen (O₂): Relights a glowing splint. – Sulfur dioxide (SO₂): Turns acidified potassium manganate(VII) from purple to colorless. 2. Demonstrate gas tests or use videos.- Plenary (10 mins): Students complete a worksheet matching gases to their tests. |
| Resources | Gas samples, reagents, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write a paragraph explaining why gas identification is important in real-life applications. |
| Assessment | Worksheet: Match gases to their identifying tests and observations. |
| Past Paper Practice | IGCSE Chemistry 0620/41/M/J/19 Q5(c). |
Lesson 4: Flame Tests for Cations
| Section | Details |
|---|---|
| Objective | – Describe and interpret flame test results for cations (Li⁺, Na⁺, K⁺, Ca²⁺, Ba²⁺, Cu²⁺). |
| Activities | – Starter (5 mins): Show a video of flame colors and ask: “Why do metals produce different flame colors?”- Main (25 mins): 1. Explain the principle of flame tests. 2. Demonstrate tests for specific cations: – Li⁺: Crimson flame. – Na⁺: Yellow flame. – K⁺: Lilac flame. – Ca²⁺: Brick-red flame. – Ba²⁺: Apple-green flame. – Cu²⁺: Blue-green flame. 3. Allow students to perform flame tests in groups or show detailed demonstrations if equipment is unavailable.- Plenary (10 mins): Students complete a worksheet matching flame colors to cations. |
| Resources | Bunsen burner, metal salts, nichrome wire, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Research and explain why flame tests are limited for mixtures of metal ions. |
| Assessment | Worksheet: Identify cations based on flame colors. |
| Past Paper Practice | IGCSE Chemistry 0620/41/O/N/21 Q5(d). |
Key Notes for Students:
- Anion Tests:
- Carbonate forms CO₂, sulfate forms a white precipitate with barium nitrate.
- Cation Tests:
- Sodium hydroxide and ammonia produce characteristic precipitates.
- Gas Tests:
- Ammonia turns red litmus blue, hydrogen pops with a lighted splint.
- Flame Tests:
- Specific cations produce characteristic flame colors (e.g., crimson for Li⁺, blue-green for Cu²⁺).
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