Topic: Experimental Techniques and Chemical Analysis – Acid–Base Titrations
Lesson 1: Acid–Base Titrations
| Section | Details |
|---|---|
| Objective | – Describe the apparatus used in acid–base titrations, including burette, volumetric pipette, and suitable indicator.- Outline the steps of a titration experiment. |
| Activities | – Starter (5 mins): Show a burette, pipette, and a conical flask and ask: “How are these tools used in chemical experiments?”- Main (25 mins): 1. Introduce titration as a method to determine the concentration of an unknown acid or base. 2. Explain the role of the following apparatus in titration: – Burette: Delivers a precise volume of titrant (e.g., acid or base). – Volumetric pipette: Accurately measures a fixed volume of the solution (e.g., alkali). – Conical flask: Contains the solution to which the titrant is added. – Indicator: Changes color at the endpoint of the titration (e.g., phenolphthalein, methyl orange). 3. Demonstrate setting up the apparatus and adding titrant drop by drop. 4. Discuss the purpose of repeating the titration for accuracy.- Plenary (10 mins): Students complete a diagram labeling the apparatus used in titration and matching each to its function. |
| Resources | Burette, pipette, conical flask, indicator solutions, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write a step-by-step procedure for performing a titration to determine the concentration of hydrochloric acid using sodium hydroxide and phenolphthalein. |
| Assessment | Worksheet: Label apparatus and match steps of titration to the correct equipment. |
| Past Paper Practice | IGCSE Chemistry 0620/41/O/N/21 Q2(a) – Acid–base titrations and apparatus use. |
Lesson 2: Identifying the End-Point of a Titration
| Section | Details |
|---|---|
| Objective | – Describe how to identify the endpoint of a titration using an indicator.- Explain why different indicators are used for strong acids, weak acids, and strong or weak bases. |
| Activities | – Starter (5 mins): Ask: “What happens when you mix an acid and a base? How do we know when the reaction is complete?”- Main (25 mins): 1. Explain the concept of an endpoint: Point at which the reaction is complete (neutralization). 2. Discuss suitable indicators and their color changes: – Phenolphthalein: Colorless in acid, pink in alkali. – Methyl orange: Red in acid, yellow in alkali. 3. Demonstrate identifying the endpoint by adding titrant drop by drop and observing the color change. 4. Explain the importance of swirling the flask to mix solutions. 5. Emphasize precision: Record the volume at the first permanent color change.- Plenary (10 mins): Students complete a worksheet matching indicators to their color changes and reactions. |
| Resources | Indicators, titration setup, color charts, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write a paragraph explaining why phenolphthalein is not suitable for a titration involving a weak acid and weak base. |
| Assessment | Worksheet: Identify the appropriate indicator for specific titration scenarios. |
| Past Paper Practice | IGCSE Chemistry 0620/41/M/J/20 Q2(b) – Identifying endpoints in titrations. |
Key Notes for Students:
- Apparatus for Titrations:
- Burette: Measures and adds the titrant.
- Volumetric pipette: Measures a fixed volume of the solution.
- Conical flask: Holds the solution being titrated.
- Indicators:
- Phenolphthalein: Used for strong acid–strong base or weak acid–strong base titrations.
- Color change: Colorless to pink.
- Methyl orange: Used for strong acid–strong base or strong acid–weak base titrations.
- Color change: Red to yellow.
- Phenolphthalein: Used for strong acid–strong base or weak acid–strong base titrations.
- Endpoint Identification:
- Add titrant drop by drop near the endpoint.
- Swirl the flask to mix solutions.
- Observe the first permanent color change.
Notes for Teachers:
- Demonstrate a full titration experiment to engage students.
- Emphasize the importance of accuracy and repeating titrations for reliable results.
- Discuss real-life applications of titrations in industries (e.g., pharmaceuticals, food testing).
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