Iodine - Add a few drops of the iodine solution to the solution (positive result – dark purple color)
Benedicts solution - Add 5mL of benedict’s solution to 8 drops of unknown solution in a test tube. Place the test tube in a boiling water bath for 5 minute. (positive result – yellow)
Paper Test (pH Level) - Drop a small amount of the food or beverage on the pH paper and match the color change with the chart on the bottle to find its pH level. (high pH - basic, low pH – acidic)
Biuret Test - Mix 2-3mL of the unknown solution with an equal amount of sodium hydroxide. Then add, drop by drop, a 0.5% copper sulfate solution. Use a stirring rod to swirl the contents of the tube gently between drop. (positive result – purple)
Bromthymol Blue - Add drops of the unknown solution to a test tube partially filled with a dilute BTB solution (positive result – yellow)
Phenolphthalein - Add drops of the unknown solution to a test tube partially filled with phenolphthalein solution (positive result – pink)
Results:
Table 1: Testing for molecules in food and beverages
Discussion:
2. You may already know something about what these food and beverages are made of. With your partner, attempt to group the food and beverages into four to nine groups based on what types of molecules you think they may contain. Record your grouping.
5. Compare your results with your initial grouping. Did all the food/beverages react in the same way? If so, what type of molecules do you suspect members of each group contains that are causing the similar reaction? If not, do you have any ideas for a new grouping system? What is the basis of the system? Be prepared to discuss your ideas in a class discussion.
No, The result from the initial grouping was different. The food reacted in different ways. The group of carbohydrate reacted differently because starch such as potato and flour are made of polymers of glucose (polysaccharide), while syrup and 7up are monosaccharide. Lemon juice should be grouped in individually within the carbohydrate, because it is a carbohydrate but strongly acidic (low PH level). Egg yolk should be defined as a protein because it reacted similarly as egg white, milk and tofu.
6. Have one member of your group record your data on the class data sheet. How do your results compare with those of others groups? How can differences be explained?
The result compared with the class result had several differences. For example half of the class, milk reacted with a color change, but another half of the class resulted with a negative reaction. Our group had a negative result for milk reacting with benedicts. We believe that this happened because the milk was expired. Therefore, the results recorded differed between groups.
STUDY QUESTIONS
1. In a class investigation, five drops of iodine indicator were added to five mL of clear food substance. The resulting solution was light brown in color. What most likely happened to the molecules in the test tube?
Since the original color of iodine is light brown and when it was added to the five mL of food substances it turned light brown. Therefore, no reaction happened to the molecules in the test tubes.
2. What kinds of molecules are most likely indicated by each of the indicators?
The four main classes of large biological molecules such as carbohydrates, lipids, proteins and nucleic are tested. If the food substance reacted with iodine then the molecules should be a polysaccharide, a carbohydrate. If it the food substances reacted with benedicts then the molecules should be a monosaccharide, a carbohydrate. If the food substances reacted with biuret then the molecules in side the food should be protein. If the substances reacted with BTB then the molecules are either carbohydrate or protein.
3. Are foods and beverages made of more than one kind of molecule? Which ones? What evidence do you have for your answers?
Yes, food and beverages can be made of more than one kind of molecules. The monomers in polysaccharides can breakdown; therefore if the chain in potato broke then there would be sugar molecules in potato too.
4. Draw the structure of a simple protein, starch, sugar, and fat molecule. What evidence do biochemists have that suggests these structures?
5. How does a chemical reaction differ from simply mixing molecules?
A chemical reaction will change the properties of the original substances, however simply mixing molecules only creates a mixture and will not change its original properties.
6. In the table below, a + indicates a color change. A blank indicates no change.
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Unknown 1 contains chains of sugar molecules. True
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Unknown 2 contains simple sugar molecules (not in chains). True
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Unknown 3 has a relatively high number of hydrogen ion. Not possible to determine from the available data
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Unknown 4 may be distilled water. True
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Unknown 5 may be distilled water. False
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Unknown 6 has a PH less than 7. Not possible to determine from the available data
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Unknown 7 contains protein but no sugar and has a PH greater than 6. False
