Subject: Life Science
Grade Level: 7th Grade
Class Dates: One class period
Overview: Fermentation is a process carried out in living cells in order to obtain energy from carbohydrates without oxygen. Produced by fermentation, ethanol (ethyl alcohol) is commonly found in alcoholic beverages, and most often used as a biofuel additive in gasoline. When wine is made, a microorganism called yeast converts glucose to carbon dioxide and ethanol, according to the following equation: glucose → ethanol + carbon dioxide. During the process, the carbon dioxide is allowed to escape (except in sparkling wines), while the ethanol is retained.
Objectives: This activity is designed for a group of four students. Students will learn firsthand about the concept of fermentation, the specific chemical reaction that occurs when yeast ferments, and how to identify ethanol.
Materials:
- 2 conical flasks fitted with a cork, glass tubing, and roughly 10cm of attached rubber tubing
- 2 normal test tubes
- Limewater
- 10% glucose solution (made by dissolving five glucose tablets in 300ml of water)
- 1 teaspoon of dried yeast
- Cotton wool wadding
- Test tube rack
- Cellotape
Activities:
Instruct students to copy down the following directions before walking them through the steps:
- Add 100ml of glucose solution to each flask.
- Place 1 teaspoon of dried yeast in one of the flasks.
- Wrap both flasks in cotton wool and fasten with cellotape. (The cotton wool wadding provides a warm environment for the yeast to multiply in the glucose solution.)
- Place the cork and tubing on each flask. Submerge the free ends of each tube in two separate test tubes containing 10 ml of limewater.
- Let stand for 12 hours.
Evaluation:
Upon completion of the lesson, ask the students the following questions:
- What differences did you notice in the limewater in each setup of the experiment?
- In which flask did you see foaming and bubbles?
- Smell the contents of each flask. Which one has an alcohol smell?
- Why were both flasks wrapped in cotton wool?
- Complete this conclusion: ______________ and glucose are needed for fermentation to occur. The products of fermentation are _____________ gas and ethanol. Carbon dioxide gas turns limewater _________________.
Adaptations:
- This experiment is best performed in a science lab, but could be also be completed in a standard classroom.
- Students may not be familiar with the odor of alcohol when asked to smell each flask. It may be helpful to suggest to them that the odor is similar to that of a felt-tipped pen.
- Students could repeat the experiment by stretching a balloon over the mouth of each flask instead of connecting the flasks to a test tube of limewater. The flask containing yeast should produce carbon dioxide gas, which will blow up the balloon.
Lab Safety Guidelines:
- Use caution: No horseplay, practical jokes, or pranks are allowed in the science classroom.
- Follow all instructions carefully, and ask your teacher if you do not understand something.
- Do not touch any equipment until instructed to do so.
- Do not eat, drink, chew gum, or taste anything in the science classroom.
- Wash your hands with soap and water before entering and leaving class.
- Wear safety goggles when instructed.
- Keep work area neat and clean. Remove all unnecessary materials.
- Clean work area and equipment when you're finished with the experiment. Dispose of all waste properly.
- Tell your teacher about any accident immediately.
- Most chemicals used in the science room are dangerous. Do not touch or smell any chemicals unless told to do so.
- Students are not allowed to enter any storage closet at any time.
- Do not remove any supplies from the science classroom without your teacher’s permission.
- Use care when handling glassware. Never pick up broken or hot glassware with your bare hands.
- Use extreme caution when using matches, burners, or hot plates. Only light burners when told to do so by your teacher, and do not put anything into a flame unless specifically instructed to do so. Do not leave lit burners unattended.
- Dress properly: Long hair must be tied back, and no dangling sleeves or jewelry is allowed. Wear closed-toe and heeled shoes. Wear lab aprons as instructed.
- Memorize the location of all safety equipment and emergency exits.
Adapted from middleschoolscience.com
