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Lesson Overview
This activity will make students familiar with the most basic biochemicals found in the tubers of yams. Besides being a basic food, the yam has been the source of starting chemicals related to steroids since the 1930s. Students will identify qualitatively two major categories of organic molecules: starches and sugars. They will also chemically convert the starch to sugars and identify the conversion
Student Ability Level and Grouping
This lab is suitable for both average and above-average chemistry students. Ideally, students should work in groups of 3 or 4 but no more than that.
Expected Student Background and Skills
Before carrying out the activity, students should
- be able to accurately measure reactants used in the activity and skillfully manipulate basic lab equipment;
- have a conceptual understanding of basic molecular structure and bonding in organic molecules;
- be familiar with metric units of measurement; and
- have a conceptual and mathematical understanding of Dalton’s law of partial pressures.
Time and Materials Required
A minimum of one 45-minute period is needed to set up equipment, measure chemicals, and start the test-tube reactions. Another class period is needed to finish collecting data, exchange data with classmates, and discuss results.
Consumables
- Starch solution
- Lugol’s solution
- Benedict’s solution
Non-consumables
- 25-mL graduated cylinder
- Metric ruler
- Marking pens or pencils
- Test tube (18 x 150 mm)
- Test-tube rack
- 250-mL beaker
- Source of boiling water
- Thermometer
Learning Objectives
After completing this activity, students should understand
- basic laboratory techniques for identifying specific organic molecules;
- the basic chemistry behind the conversion of one molecule to a different one and be able to identify it;
- the structural changes that occur in the conversion of starch to a simple sugar; and
- the role of enzymes, temperature, and concentration of reactants in the rate of a chemical reaction.
In addition, students should be able to
- examine data to determine what factors have the greatest influence on the rate of a reaction, and
- draw conclusions based on trends in experimental data.
National Science Education Standards
Unifying Concepts and Processes
- Evidence, models, and explanations
- Change, constancy, and measurement
Science as Inquiry
- Abilities necessary to do scientific inquiry
- Understandings about scientific inquiry
Physical Science
- Chemical reactions
Science in Personal and Social Perspective
- Science and technology in society
History and Nature of Science
- Science as human endeavor
- Nature of science
- History of science
Classroom activities are provided through the generous support of the Biogen Idec Foundation.