Organic Compounds Problem: Based on the color of the indicator, which type of organic compound will be found in each type of food? Hypothesis: If Benedict solution is added to honey, then it will turn. If Biuret solution is added to egg whites, then it will turn. If Benedict solution is added to corn oil, then it will turn. If Benedict solution is added to glucose, then it will turn. If Benedict solution is added to gelatin, then it will turn. If Benedict solution is added to butter, then it will turn. If iodine is added to starch, then it will turn.
If Benedict color is added to apple juice, then it will turn. If any organic substance is tested with distilled water, then nothing will happen. Materials: -12 test tubes -Test tube rack -Test tube clamp -Well tray -Hot water bath -Paper towels -Brown paper -Iodine solution -Biuret solution -Benedict’s solution -Honey solution -Egg white and water -Corn oil -Glucose solution -Gelatin and water -Melted butter -Starch and water -Apple juice and water -Distilled water Procedure: Part A: Testing for Carbohydrates: Monosaccharides Monosaccharides can be identified in a substance using an indicator called
Benedict’s solution. When Benedict’s is heated in the presence of a monosaccharide, the color changes from blue to green to yellow to reddish-orange, depending on the amount of monosaccharide present. 1. Add 5mL of a sample to a test tube. Add 5 drops of Benedict’s solution to the test tube. 2. Place the test tube in the hot-water bath. Heat the test tube for 1 to 2 minutes, or until the indicator changes color, if it changes color. 3. With a test tube holder, remove the tube from the hot-water bath and place it back in the test tube rack. 4. Record any changes in your data table.
Part B: Testing for Carbohydrates: Polysaccharides Polysaccharides can be tested for using the indicator Iodine. Iodine will change color from yellow-brown to blue-black in the presence of starch. 1. Add one dropper-full of a sample to a well in the well tray. 2. Add 2-3 drops of Iodine to the sample. 3. Record any changes in your data table. Part C: Testing for Lipids Lipids can be tested for using the “sack lunch” method: the lipid is rubbed into a brown bag. If the paper appears translucent (a grease spot appears), then a lipid is present in the food. 1.
Tear a small square from a piece of brown paper. Write the name of one test substance. Add a few drops of each solution to the paper. 2. Rub the solution until a “wet” spot appears on the paper. 3. Set the paper aside until the spot appears to dry. 4. Hold the brown paper up to a bright light. 5. Record observations in data table. Part D: Testing for Proteins Proteins can be tested for using Biuret’s reagent, which reacts with the peptide bonds between amino acids in the polypeptide. Biuret’s reagent turns from blue to purple-violet if peptide bonds are present. . Add one dropper of a sample to a clean well in the well tray. 2. Add 3 drops of Biuret’s reagent to the sample. 3. Record any changes in color. Data Table: | A| B| C| D| | Monosaccharide Test| Polysaccharide Test| Lipid Test| Protein Test| | Benedict Color| Glucose +/-| Iodine color| Starch +/-| Translucent? | Lipid +/-| Biuret color| Protein +/-| 1. Honey| Yellow| +| Brown| -| No| -| Yellow| -| 2. Egg White| Blue/purple| -| White| -| No| -| Purple| +| 3. Corn Oil| Blue| -| Brown| -| Yes| +| Yellow| -| 4. Glucose| Yellow| +| Brown| -| No| -| Clear| -| . Gelatin| Purple| -| Brown| -| No| -| Purple| +| 6. Butter| Yellow| +| Brown| -| Yes| +| Clear| -| 7. Starch| Yellow| +| Black| +| No| -| Yellow| -| 8. Apple Juice| Yellow| +| Brown| -| No| -| Yellow| -| 9. Distilled Water| Blue| -| Brown| -| No| -| Clear| -| Analysis Questions: Most of the food substances we tested contained at least one of the organic compounds. The two food substances that had the most were butter and starch. The organic compounds that are most common in foods that come from plants are carbohydrates.
However, the organic compounds that are most common in animal meat are proteins. The original colors of the food substances did affect our test results. For example, if the substance was yellow, such as apple juice, and we were trying to test for glucose, we could not tell if the substance had changed colors or if it was just yellow because it was apple juice. Distilled water did not contain any of the organic compounds we tested because the purpose of using it was to provide a control group. If distilled water did, in fact, test positive for an organic compound, we could conclude two things.
It was either contaminated or it was not actually distilled. The observations in this investigation could help us decide whether or not a substance is safe for a diabetic to eat by testing it. If it tests positive for glucose or starch, it is a carbohydrate and should be avoided. Biuret solution changes color when it reacts with a protein. In your skin, there are a lot of proteins, therefore when Biuret solution comes in contact with skin it turns a brownish-purple color. Conclusion: Were your hypotheses supported or refuted?
Discuss the data that caused you to decide whether your hypothesis was valid or not. What did you learn in this experiment? Were there any sources of error? All of my hypotheses were supported with the exception of my hypothesis on corn oil. I stated that “If Benedict solution is added to corn oil, then it will turn”. The data that caused me to decide that my hypothesis was not valid was the fact that when we added Benedict solution to the corn oil, it stayed blue, proving that there was no glucose present at all.
In this experiment, I learned that almost all sources of food contain at least one form of an organic substance. I also learned that when a glucose is present, Benedict solution will change from blue to yellow or orange-red, when a starch is present the iodine color will change from brownish to black, when a lipid is present the solution will become transparent when dried on a brown paper towel, and when a protein is present the Biuret solution will turn from light blue to purple. In our lab, there were no sources of error.