Chromatography

Active learning helps students connect abstract concepts like solubility and adsorption to concrete visual outcomes. When students physically run paper and thin-layer chromatograms, they see how ink components travel at different speeds, which builds durable understanding of separation science.

• Year 11
• Chemistry
• 4 activities
• 30 min–50 min

Learning Objectives

1. Explain the principles of separation in paper and thin-layer chromatography, relating them to differences in polarity and solubility.
2. Calculate Rf values accurately from experimental data and use them to identify unknown substances by comparison with known standards.
3. Analyze chromatograms to determine the number of components in a mixture and assess the purity of a sample.
4. Compare and contrast the advantages and disadvantages of paper chromatography versus thin-layer chromatography for specific analytical tasks.

Project-Based Learning

⏱ 50 min·Small Groups

Small Group Practical: Ink Separation by Paper Chromatography

Provide chromatography paper, inks, solvents, and beakers. Students mark origin lines, apply ink spots, place paper in solvent chambers, and observe separations after 20 minutes. They dry strips, measure distances, and calculate Rf values for each band.

Prepare & details

Explain the principles of paper and thin-layer chromatography.

Facilitation Tip: During the Small Group Practical, encourage students to rotate roles (recording data, adjusting solvent level, observing) so everyone contributes to the scientific process.

Setup: Flexible workspace with access to materials and technology

Materials: Project brief with driving question, Planning template and timeline, Rubric with milestones, Presentation materials

• Apply
• Analyze
• Evaluate
• Create
• Self-Management
• Relationship Skills
• Decision-Making

Project-Based Learning

⏱ 30 min·Pairs

Pairs Task: Rf Value Calculations and Identification

Supply printed chromatograms from known and unknown mixtures. Pairs measure distances with rulers, compute Rf values, and match unknowns to standards using a provided table. They discuss matches and potential errors in measurement.

Prepare & details

Describe how Rf values are used to identify components in a mixture.

Facilitation Tip: During the Pairs Task, require students to justify their Rf calculations aloud before checking reference values to reinforce reasoning over guessing.

Setup: Flexible workspace with access to materials and technology

Materials: Project brief with driving question, Planning template and timeline, Rubric with milestones, Presentation materials

• Apply
• Analyze
• Evaluate
• Create
• Self-Management
• Relationship Skills
• Decision-Making

Project-Based Learning

⏱ 40 min·Whole Class

Whole Class Demo: Thin-Layer Chromatography of Food Dyes

Demonstrate TLC by spotting food colorings on plates, developing in solvent, and visualizing under UV light. Class records observations, compares to paper results, and notes speed advantages. Follow with Q&A on technique differences.

Prepare & details

Analyze the applications of chromatography in forensic science and food analysis.

Facilitation Tip: During the Whole Class Demo, pause after each step to ask students to predict the next outcome based on what they see happening on the plate.

Setup: Flexible workspace with access to materials and technology

Materials: Project brief with driving question, Planning template and timeline, Rubric with milestones, Presentation materials

• Apply
• Analyze
• Evaluate
• Create
• Self-Management
• Relationship Skills
• Decision-Making

Project-Based Learning

⏱ 45 min·Small Groups

Inquiry Lab: Optimizing Chromatography Conditions

Groups test solvents or temperatures on identical mixtures, run parallel chromatograms, and compare separations. They hypothesize improvements and present findings on how conditions affect Rf values.

Prepare & details

Explain the principles of paper and thin-layer chromatography.

Setup: Flexible workspace with access to materials and technology

Materials: Project brief with driving question, Planning template and timeline, Rubric with milestones, Presentation materials

• Apply
• Analyze
• Evaluate
• Create
• Self-Management
• Relationship Skills
• Decision-Making

Teaching This Topic

Start with a simple paper chromatography activity to ground students in the core idea of separation based on affinity. Move to thin-layer chromatography only after students can explain paper results, as it adds complexity that can confuse novices. Research shows hands-on labs followed by explicit calculation practice build both conceptual and procedural fluency in chromatography.

What to Expect

Successful learning looks like students explaining why components separate differently, calculating Rf values accurately, and choosing the right chromatography method for a given task. They should also recognize that conditions affect results and that chromatography is primarily for analysis, not purification.

Watch Out for These Misconceptions

Common Misconception

During the Small Group Practical: Ink Separation by Paper Chromatography, watch for students who believe separation happens because bigger particles can't move through the paper.

What to Teach Instead

During the Small Group Practical, ask students to compare the migration of different ink colors from the same pen. Prompt them to notice that some colors travel farther even though the ink particles are the same size, guiding them to see solubility and adsorption as the real drivers of separation.

Common Misconception

During the Pairs Task: Rf Value Calculations and Identification, watch for students who treat Rf values as absolute labels for substances.

What to Teach Instead

During the Pairs Task, have students recalculate Rf values using solvents of different polarities. Ask them to explain why the same dye’s Rf changes, reinforcing that Rf is conditional and must be compared under identical conditions.

Common Misconception

During the Inquiry Lab: Optimizing Chromatography Conditions, watch for students who assume chromatography always produces pure components ready for use.

What to Teach Instead

During the Inquiry Lab, have students attempt to collect separated components by cutting the paper or plate. Ask them to reflect on how much of each component they actually collected and whether it’s truly pure, highlighting chromatography’s role in analysis rather than purification.

Assessment Ideas

Quick Check

After the Small Group Practical, provide students with a pre-run chromatogram. Ask them to calculate the Rf value for two spots and explain what a higher Rf indicates about the component’s interaction with the mobile and stationary phases.

Discussion Prompt

After the Whole Class Demo, pose the question: 'You need to separate two food dyes quickly and cheaply for a school project. Would you use paper or thin-layer chromatography? Compare speed, resolution, and cost in your reasoning.' Facilitate a class discussion comparing their choices and evidence.

Exit Ticket

During the Pairs Task, give students a chromatogram of an unknown mixture alongside chromatograms of known pure substances. Ask them to identify which known substance is present in the unknown and provide Rf values as evidence, collecting these as they leave.

Extensions & Scaffolding

• Challenge students to separate a mixture of two inks they choose themselves, then present their method and results to the class.
• Scaffolding: Provide pre-marked filter paper with solvent front lines and component starting points to reduce setup errors.
• Deeper exploration: Have students research how chromatography is used in real-world fields like forensics or food safety, then design a short presentation on one application.

Key Vocabulary

Stationary phase	The solid or liquid material that does not move during chromatography. In paper chromatography, this is the water molecules adsorbed onto the cellulose paper.
Mobile phase	The solvent or gas that moves through the stationary phase, carrying the components of the mixture with it.
Rf value	The retention factor, calculated as the distance traveled by a spot divided by the distance traveled by the solvent front. It is a ratio and is unitless.
Eluent	The solvent used as the mobile phase in chromatography. Its properties, such as polarity, affect the separation of components.