Topic: Experimental Techniques and Chemical Analysis – Chromatography
Lesson 1: Introduction to Paper Chromatography
| Section | Details |
|---|---|
| Objective | – Describe how paper chromatography separates mixtures of soluble substances.- Understand the use of suitable solvents in chromatography. |
| Activities | – Starter (5 mins): Show a filter paper with ink spots and ask: “How can we separate the colors in this ink?”- Main (25 mins): 1. Explain the principle of chromatography: Separation based on solubility and interaction with the paper (stationary phase) and solvent (mobile phase). 2. Demonstrate setting up a simple chromatography experiment: – Draw a pencil line on chromatography paper. – Place small spots of ink or dye on the line. – Suspend the paper in a beaker with the solvent (below the pencil line). 3. Observe and explain the separation as the solvent moves up the paper, carrying the components of the mixture. 4. Discuss the importance of using a suitable solvent (e.g., water for polar substances, ethanol for nonpolar substances).- Plenary (10 mins): Students complete a diagram labeling the components of a chromatography experiment. |
| Resources | Chromatography paper, inks/dyes, solvents, beakers, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write a paragraph explaining how chromatography can be used to separate the colors in a food dye mixture. |
| Assessment | Worksheet: Label a chromatography setup and describe the steps involved. |
| Past Paper Practice | IGCSE Chemistry 0620/41/O/N/21 Q3(a) – Principles of chromatography. |
Lesson 2: Locating Agents and Analyzing Chromatograms
| Section | Details |
|---|---|
| Objective | – Describe the use of locating agents for colorless substances.- Interpret chromatograms to identify unknown and pure/impure substances. |
| Activities | – Starter (5 mins): Show a chromatogram with visible and invisible spots and ask: “How can we detect invisible substances?”- Main (25 mins): 1. Explain locating agents: – Chemicals that react with colorless substances to make them visible (e.g., UV light, chemical sprays). 2. Demonstrate using a locating agent (if possible) to reveal spots on a chromatogram. 3. Discuss how to analyze chromatograms: – Pure substances produce a single spot. – Mixtures produce multiple spots. – Unknown substances are identified by comparing their positions with known substances. – Plenary (10 mins): Students interpret a provided chromatogram to identify pure/impure substances and match unknowns to known references. |
| Resources | Chromatograms, locating agents (if possible), worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Write a brief explanation of how locating agents are used to detect colorless substances in chromatography. |
| Assessment | Worksheet: Analyze chromatograms and identify unknown substances. |
| Past Paper Practice | IGCSE Chemistry 0620/41/M/J/20 Q3(b) – Analyzing chromatograms. |
Lesson 3: Calculating RfR_f Values
| Section | Details |
|---|---|
| Objective | – State and use the equation for RfR_f: Rf=distance travelled by substancedistance travelled by solventR_f = \frac{\text{distance travelled by substance}}{\text{distance travelled by solvent}}. |
| Activities | – Starter (5 mins): Show a chromatogram and ask: “How can we quantify the separation of substances in this chromatogram?”- Main (25 mins): 1. Introduce the RfR_f value as a ratio describing how far a substance travels relative to the solvent front. 2. Write the formula: Rf=distance travelled by substancedistance travelled by solventR_f = \frac{\text{distance travelled by substance}}{\text{distance travelled by solvent}}. 3. Demonstrate measuring distances on a chromatogram using a ruler: – Measure from the baseline to the center of the spot (substance). – Measure from the baseline to the solvent front. 4. Calculate RfR_f values for several spots on a chromatogram. 5. Discuss how RfR_f values are used to identify substances by comparison with reference values.- Plenary (10 mins): Students practice calculating RfR_f values for provided chromatogram data. |
| Resources | Chromatograms, rulers, worksheets. |
| Time | 40 minutes total: 5 mins (Starter) + 25 mins (Main) + 10 mins (Plenary). |
| Homework | Calculate the RfR_f values for a given chromatogram and compare with reference values to identify substances. |
| Assessment | Worksheet: Measure and calculate RfR_f values from chromatograms. |
| Past Paper Practice | IGCSE Chemistry 0620/41/O/N/21 Q3(c) – Calculating and using RfR_f values. |
Key Notes for Students:
- Chromatography Basics:
- Separates mixtures based on solubility and interaction with the paper and solvent.
- Suitable solvent choice is crucial for effective separation.
- Locating Agents:
- Help visualize colorless substances in chromatograms.
- Analyzing Chromatograms:
- Pure substances: Single spot.
- Mixtures: Multiple spots.
- Identify unknowns by comparing with known references.
- RfR_f Value:
- Rf=distance travelled by substancedistance travelled by solventR_f = \frac{\text{distance travelled by substance}}{\text{distance travelled by solvent}}.
- Used to quantify and identify substances in chromatograms.
Notes for Teachers:
- Use hands-on chromatography experiments to enhance understanding.
- Relate chromatography to real-world applications (e.g., food testing, forensics).
- Emphasize accuracy in measuring distances and calculating RfR_f values.
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