Summer Research Program for Science Teachers

Marietta Cleckley

Using Chromatography to Identify Unknowns

Lesson 1 - An Introduction to Chromatography

• Objectives:  Students will define chromatography and related terms. They will observe paper and thin layer chromatography and identify the principles of both.

• Motivation:  Ask students: "How many different colors are in black ink?"   "Does anyone know a way for us to determine this?"

• Demonstrate separating the ink colors using a beaker of water, felt tip marker, and chromatography paper.

• Explain/describe the process of chromatography using the demonstration. [9-12 Content Standard E- Understandings about science and technology] Define solution, solvent, solubility, and chromatography. [9-12 Content Standard B- Properties of matter] Explain what is meant by the distance the solvent travels.  [9-12 Content Standard B- Motions and forces] Describe how this process is used in science.  Explain that all substances may not be soluble in water.  Therefore, other solvents are used depending on what solutes are being dissolved.  Give examples: nail polish remover and acetone; chlorophylls and alcohol.

• Separation of other ink colors may be demonstrated if time permits.

Lesson 2 - Experimental Design

• Objectives: Students will use experimental design sheets and laboratory reference sheets to develop an experiment using chromatography to identify substances in an unknown solution. Design worksheets will be evaluated and critiqued by the teacher. [Teaching Standard B- Focus and support inquiry while interacting with students] Correction/adjustments will be made before experiments will be conducted.

• Motivation: Hand out Experimental Design Worksheet. Ask students to name elements of a good experiment.  List responses on a board. [Teaching Standard B- Orchestrate scientific discourse]

• Direct students into teams to design an experiment for the problem given.  The teacher may also want to have copies of other experiments involving chromatography for those students who may need help getting started.

• Collect all design worksheets at the end of the period.

Lesson 3 - Identifying Substances in an Unknown Solution

• Objectives: Students will set up and conduct the experiments they have designed.  They will complete written lab reports including research findings and conclusions.

• Give each group a copy of their Experimental Design Worksheet with comments/corrections/changes.

• Direct students to collect materials and conduct their experiment. [9-12 Content Standard A- Design and conduct a scientific investigation]

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