Lab 4: Testing Carbohydrates

Lab 4: Testing Carbohydrates

Testing Carbohydrates LabName:

Biology 6.0 Date: Period:

Pre-lab:

  1. Write out the objective of the lab.
  2. Answer all of the questions in the prelab.
  3. Write the procedure summary.
  4. Include ALL data tables for the lab.

Pre-Lab Questions:

  1. Give an example and the formula of a monosaccharide.
  2. Give an example and the formula of a disaccharide.
  3. Give an example of a polysaccharide. What is the ratio of H:O?
  4. Give an example of something that is not a carbohydrate.How do we know this is NOT a carbohydrate?
  5. A chemical indicator is a special chemical that reacts specifically with another substance. The way in which we know the indicator has reacted is a color change. Sometimes the color change is spontaneous, while other times an input of energy is necessary. What form of energy do you think is the easiest form of energy to input in a biology classroom? ______There are two ways to insert this energy - direct flame or hot water bath. We are going to choose the later for this lab.
  6. There are two chemical indicators that help identify different forms of carbohydrates. If there are only two types of chemical indicators, how do you think we will be able to identify the third type of carbohydrate?

Benedict’s solution (blue solution) and Iodine (reddish solution) are two indicators that will be used in this lab to help determine the type of sugar(s) found in 5 unknown bottles. In the 1stpart of the lab, you will determine how the indicators work with the carbohydrates. In the 2ndpart of the lab, you will use your new found knowledge to determine the types of sugar(s) found in the 5 unknown bottles.

  1. This lab is a very qualitative lab. Why do you think that we don’t need to be very accurate with our measurements for this lab?

Procedure:

Materials: 1 bottle of iodine, 1 bottle of benedict’s solution, 6 test tubes, 2 large test tubes, test tube rack, test tube clamp

PART I: Indicators with known carbohydrates

  1. Label all of your test tubes. See procedure for labeling.
  2. Fill a test tube with 3-4 mL of distilled water. This will be your height reference for all solutions in the lab.
  3. Fill another test tube with distilled water to about the same height as the first test tube.
  4. Fill 1 test tube with the monosaccharide – same height as the dI water.
  5. Fill another test tube with the disaccharide solution – same height as the dI water.
  6. Fill a third test tube with the polysaccharide solution – same height as the dI water..
  7. Add 4 drops of iodine todistilled water. Add 4 drops of iodine to one test tube of each type of sugar solution. Record your observations. Did a color change occur?

Put these questions in your post-lab section.

  • The distilled water will be used as a comparison for the carbohydrate solutions. Why?
  • Is this reaction with iodinespontaneous?
  • Do you think you have figured out what type of carbohydrate iodine indicates? If so, what type?
  • If iodine tests for (see above), what type of sugars does that leave Benedict’s to test for in this lab?
  1. Clean and rinse the three test tubes containing the carbohydrates. Do not discard the dI water.
  2. Fill the three test tubes with the carbohydrates following steps 3-5.
  3. Add 15 drops of Benedict’s solution todistilled water.
  4. Add 15 drops of Benedict’s solution to the other test tubesfor each type of sugar solution. Record your observations. Did a color change occur?

Put these questions in your post-lab section.

  • What do you think is going to be needed at this point? (Because you probably were expecting something to happen spontaneously….sorry, it doesn’t)
  • Does this automatically mean that this reaction is endothermic? Why or why not?
  1. Place your test tubes into the hot water bath – not boiling. Make sure you can identify which type of sugar is in the test tube that is why they are labeled.
  2. Once you see a color change occurring in one of the test tubes you can take them out of the hot water bath. Please use the test tube clamps.

Put this question in your post-lab section.

  • What did you conclude from this step?

Summary of Part I:Put these questions in your post-lab section.

  • How do you determine if a substance is a monosaccharide?
  • How do you determine if a substance is a disaccharide?
  • How do you determine if a substance is a polysaccharide?

Part II: Identifying the unknowns

Now that you understand HOW the chemicals work and how much of the substances you need in order to complete the task, you will NOT be given too many direct instructions to follow.

Task: What types of sugar(s) are found in each of the 5 unknown solutions.

Create an easy to read data table below which will organize your observations, results, and interpretations in organized fashion. Use a straight edge to do this neatly.

Post Lab:

Complete all questions within the procedure. Answer the following questions:

  • Suppose you were given an unknown and you receive a negative result for both the iodine test and the Benedict’s solution test. What type of carbohydrate would you assume you had in the unknown?
  • What is the problem with this assumption?
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