Chemical Analysis: Purity, Formulations, Chromatography, and Gas Tests
This lesson covers the fundamental concepts of chemical analysis for Year 11. Students will explore the definition of pure substances versus formulations, learn how to identify purity using thermal data, perform chromatography calculations, and master the four standard gas tests required by the GCSE specification.
Learning objectives
- Distinguish between pure substances and mixtures using melting and boiling point data.
- Define and identify examples of formulations in everyday life.
- Calculate and interpret Rf values from paper chromatography.
- Describe and identify the chemical tests for hydrogen, oxygen, carbon dioxide, and chlorine gas.
Lesson plan (60 minutes)
Introduction · 5 min
Do Now: Defining mixtures vs compounds and listing properties of water.
Direct Instruction · 10 min
Teacher Explainer: Pure substances, formulations, and the science of chromatography.
Demonstration · 5 min
Worked Example: Calculating Rf values and interpreting chromatograms.
Independent Practice · 25 min
Differentiated Worksheet Activity: Students work through Support, Core, or Stretch tasks.
Practical Demonstration · 10 min
Gas Tests Practical Demo: Quick demonstration of O2, H2, CO2 and Cl2 tests.
Review · 5 min
Plenary: 8-question multiple choice quiz and self-marking.
Key vocabulary
- Pure Substance
- A single element or compound, not mixed with any other substance.
- Formulation
- A mixture that has been designed as a useful product.
- Chromatography
- A technique used to separate the components of a mixture based on their solubility.
- Stationary Phase
- The phase that does not move (e.g., the paper in chromatography).
- Mobile Phase
- The phase that moves (e.g., the solvent in chromatography).
Core worksheet (first questions)
- Explain the difference between the melting point of a pure substance and a mixture.
- Give three examples of common formulations.
- Why must the baseline in chromatography be drawn in pencil rather than ink?
- A spot moved 4.5 cm and the solvent moved 6.0 cm. Calculate the Rf value.
Quiz (sample)
1. In chemistry, what is the definition of a 'pure' substance?
- A. A substance with a low boiling point
- B. A single element or compound not mixed with any other substance
- C. A mixture of different chemicals that are not joined
- D. A chemical that has been filtered multiple times
2. How can you tell if a substance is pure using melting point data?
- A. It melts at a lower temperature than expected.
- B. It boils over a wide range of temperatures.
- C. It has a single, fixed melting point.
- D. It changes colour when it melts.
3. What is a formulation?
- A. A complex mixture designed as a useful product.
- B. A chemical reaction that creates a gas.
- C. A pure element found in nature.
- D. The result of a chromatography experiment.
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