A Pre-Treatment Model for Ethanol Production Using a Colorimetric Analysis of Starch Solutions
This module focuses on the production of sugar (glucose and maltose) from cornstarch. The first lesson from this module relates glucose production from cornstarch to ethanol fuel production from corn stover. Another lesson uses a calculator based colorimeter interface from the Vernier® Company to quantify the hydrolysis of starch to sugar by salivary amylase. In this lesson saliva is added to a starch solution containing a couple of drops of iodine. Light initially doesn’t pass through this solution. If the absorption decreases after the addition of the saliva, this means more light is passing through and the starch is being hydrolyzed (broken down into maltose and glucose). The third lesson again uses colorimetry but this time to measure starch hydrolysis by dilute (1% volume to volume) sulfuric acid. Finally, we offer suggestions for using starch hydrolysis and colorimetry as a basis for student designed experiments.
Time Required: Five 45 minute periods
•Recognize the environmental and economic benefits of ethanol as a fuel additive.
• Identify ethanol as a product of sugar fermentation.
• Know that photosynthesis produces complex carbohydrates polysaccharides).
• Understand that hydrolysis is a technique used by chemists to break polysaccharides into saccharides that can be fermented.
• Demonstrate that starch can be hydrolyzed by salivary amylase.
• Demonstrate appropriate safe laboratory behavior and techniques while mixing chemicals.
• Follow correct procedures for using a colorimeter.
• Document observations and data in an organized appropriate laboratory format.
• Analyze and interpret the results of the colorimetric data and observations.
• Communicate their results orally.
Day one: Introduce students to concepts related to the significance and production of ethanol as a renewable resource and fuel. (See teacher background information.)
Day two: Students hydrolyze a solution of corn starch and distilled water in saliva (salivary amylase) and make comparisons using the colorimeter.
Corn starch does not dissolve in water. Therefore, it will be necessary to frequently and vigorously mix it at strategic times during this inquiry, such as before decanting or placing in the colorimeter. It may be necessary to vigorously mix the cuvettes during their colorimetric analysis.
Also, salivary amylase hydrolyzes starch over time. Consequently, it may be valuable for students to prepare their mixtures with starch solution one day before collecting their colorimetric data.
Colorimetric analysis should be performed at a wavelength of 635 nm. At this wavelength the color change from the addition of iodine does not interfere with the effects of salivary amylase on the starch. (You may wish to have students check the absorption of just water with a couple of drops of iodine in it. At 635 nm the absorption should be zero. Ask the students why? Answer: the iodine solution is reddish yellow. This means the solution absorbs other colors but reflects reddish yellow. The wavelengths of yellow to red range from about 570 nm to 700 nm. 635 nm falls right in the middle of that range.)
• In a 100 ml graduated cylinder prepare a stock sample of 0.5g of corn starch in 100ml of water. (Individual student groups will need less than 10 ml of this sample.)
• Calibrate the colorimeter with 3 ml of distilled water in a cuvette.
• Prepare and analyze a blank sample cuvette of 3 ml of distilled water and one drop of iodine.
• One student, who hasn’t eaten in a while, collects about 10 ml of saliva.
• Prepare and analyze one test sample cuvette by pipetting 1.5 ml of stock solution and 1.5 ml of saliva and record colorimetric data.
• Prepare and analyze a second test sample cuvette by pipetting 1.5 ml of stock solution and 1.5 ml of saliva and adding one drop of iodine and record colorimetric data. (The absorbance should decrease with time in this sample. This shows that the starch is changing, but it doesn’t show that glucose is formed. A Benedict’s solution test could be done as a demonstration at this point.)
Day three: Acid hydrolysis of corn starch and colorimetric analysis of the acid solution and saliva. Repeat the steps given for day one only substitute 1% sulfuric acid for distilled water. Prepare a 1% sulfuric acid solution by adding 1ml of concentrated sulfuric acid to 99 ml of distilled water.
• In a 100 ml graduated cylinder prepare a stock sample of 0.5g of corn starch in 100ml of water1% sulfuric acid. (Individual student groups will need less than 10 ml of this sample.)
• Calibrate the colorimeter with 3 ml of 1% Sulfuric Acid in a cuvette
• Prepare and analyze a blank sample cuvette of 3 ml of 1% Sulfuric Acid and one drop of iodine
• One student who hasn’t eaten in a while collects about 10 ml of saliva
• Prepare and analyze one test sample cuvette by pipetting 1.5 ml of stock solution of 1% sulfuric acid and 1.5 ml of saliva and record colorimetric data
• Prepare and analyze a second test sample cuvette by pipetting 1.5 ml of stock solution of 1% sulfuric acid and 1.5 ml of saliva and adding one drop of iodine and record colorimetric data.
Group Homework for Inquiry Lab: Students create an experiment involving starch hydrolysis and colorimetry. Students write the title, purpose, materials, and methods for their experiment.
Some possibilities for further inquiry include testing the affect of temperature on the amylase in saliva, seeing how temperature affects the rate of starch hydrolysis, testing individual differences in the amounts of amylase in each others’ saliva, testing dog saliva (if a student has a “drooly” dog), or seeing if exercise affects the amylase concentration in saliva.
These are only suggestions. You may wish to encourage students to come up with their own questions.
Day four: Students perform experiments of their choosing or design. (See our list of possibilities in the Group Homework for Inquiry Lab section above.)
Day five: Discussion and Evaluation
See Teacher Background Information on page 7 of the attached lesson plan.
- Use a lab rubric to evaluate the experiment. Students could be assessed on participation, safe lab techniques and proper methodologies.
- A written lab report could be evaluated by the teacher or by student groups.
- Use a rubric or score student presentations on the results and conclusions from the experiments they created.
- Have students write an essay summarizing the environmental and economic impacts of ethanol blended gasoline.
- Have students summarize the basic ideas behind colorimetry and how the colorimeter showed the hydrolysis of starch.
-Protective eye wear -Vinyl gloves -Lab apron -Graduated cylinder -250 ml beaker -Stirring rod -Distilled water -Four to eight 15ml test tubes and stoppers per group -Labels for glassware -Waterproof pen -Notebook -Mass balance -Weighing paper -Vernier LabPro and cords (Order Code: LABPRO Price: $220 - http://vernier.com/ ) -Vernier Colorimeter and cuvettes (Order Code: COL-BTA Price: $110 - http://vernier.com/ ) -Kimwipes -Disposable pipettes -Carolina Biological Supply (Product Code 73-6984, 3.0 ml capacity, Price: $4.10 Pack of 100 http://carolina.com ) -TI Graphing Calculator (preferably TI-83 Plus Silver Edition) -Corn Starch (grocery item) -Iodine Tincture (pharmaceutical item. There are hazards for Iodine Tincture. Please know and follow all safety measures.)
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