Mentoringk12.pbworks.com
Purpose of Lab – Students will use chemical reagents to test food items for the presence of glucose and starch.
Hypothesis: Students will develop a hypothesis for lab. Example: If I test my unknown substance with Benedict solution and iodine, then I can find out if my unknown is composed of glucose or starch.
Materials Used During Lab –
• The teacher will need to make 2 mixtures prior to this lab: (glucose and water mixture) and (starch and water mixture) Use Argo corn starch for starch and Dextrose for glucose.
• For the glucose mixture, mix about two teaspoon of glucose with 200 mls of water.
• For the starch mixture, mix about one teaspoon of starch with 200 mls of water.
• You will need 2 test tubes for teacher testing of glucose and starch.
• Select several carbohydrate food items for testing. Good glucose items to test are:
white grape juice, apple juice, grapefruit juice, light colored fruit juices, Gatorade, Powerade Good starch items for testing are: spaghetti, rice, oatmeal, grits, crackers, flour, bread, chips
• Place all materials in the first column on a tray for the “Materials Collector” to pick up.
• Each student group will need one test tube of glucose solution and one test tube of starch solution for their control group
• Each student group will need 2 test tubes containing 2 mls of the same unknown substance for their experimental group
• Give each unknown substance a number and place the number on the test tube.
• Have students explain why some foods test both positive for glucose and starch.
|Materials for each group |Materials that will be shared by several groups |
|Goggles |Hot water bath consisting of hot plate with large beaker – |
| |approximately filled 1/3rd with water. |
|One test tube with about 2mls of glucose solution |Test tube holders |
|One test tube with about 2 mls of starch solution | |
|2 test tubes of the same unknown substance | |
|One dropper bottle of Iodine solution | |
|One dropper bottle of Benedict solution | |
|One test tube rack | |
|Beaker for transporting test tube to hot water bath | |
|Laboratory aprons for each student | |
Misconceptions to Address by Teacher:
• Students will need help in understanding the purpose of an indicator. They will ask, “Why did that substance turn orange?” “Why did a color change take place?” Make sure students understand that the iodine and Benedict solution (not glucose or starch) are changing color.
Safety Issues:
• Caution students about the presence of hot water during the lab and only allow the “Materials Collector” to move about the room.
• Make sure all students wear safety goggles and aprons during the lab
• Locate the hot water baths in secure areas in the room.
• A hot pot may be easier to manage and can be used in the place of a hot water bath.
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