SBI 3CLab Activity #1: Testing for Macromolecules
Purpose:To determine which type of macromolecule makes up certain food items.
Materials:distilled water6 test tubeseye droppertest tube holders
iodine solutionBiuret ReagentBenedict’s solutionSudan IV solution
hot plate300 mL beaker10 mL graduated cylinder
Samples: ______
______
Biuret Reagent (copper sulphate & potassium hydroxide) / Benedict’s Solution / Iodine Solution / Sudan IV SolutionReacts with proteins, turns purple or pink / Reacts with sugars, turns green (less sugar) – yellow – orange (more sugar) after heated / Reacts with starch, turns brown to black / Reacts with lipids, turns bright red
Procedure:
Part 1: Testing for Carbohydrates (Sugars)
- Prepare a water bath by placing 250 mL of tap water into the large beaker and placing the beaker on a hot plate. Bring the temperature to near a boil (simmer). Maintain the water level by adding more water if necessary. While the water is heating, read through the method and prepare materials.
- Using masking tape, label one of the test tubes control and label the remaining 5 test tubes to correspond with the 5 food samples you will test.
- Using the graduated cylinder, add 10 mL of distilled water to the control test tube. Add 6 drops of Benedict’s to the test tube. Carefully mix the contest of the test tube by gently swirling it in a circle. Place the test tube in the warm water bath for 3 minutes.Record the colour of the solution in Table 1 – Control Results. You now know what colour the solution will be if no sugars are present in a sample.
- Place a small sample of each food in the appropriately labelled test tubes. Add 5 drops of Benedict’s to each sample. Swirl gently to mix.
- Place the 2 of the samples in the warm water bath for 3 minutes. After 3 minutes use the test tube clamp to place it in the test tube rack and heat remaining test tubes for 3 minutes. Place in rack, turn off heat and leave water bath on hot plate to cool.
- Record your results in Table 1.2 – Sugar Data Table.
- Pour out contents of test tubes and wash test tubes carefully.
Part 2: Testing for Carbohydrates (Starches)
- Using the graduated cylinder, add 10 mL of distilled water to the controltest tube. Add 5 drops of iodine to the test tube. Carefully mix the contents of the test tube.
- Record the colour of the solution in Table 1 – Control Results. You now know what colour the solution will be if no starches are present in a sample.
- Using the same foods as tested in Part 1, add a small amount to the already labelled test tube.
- Add 5 drops of iodine to each test tube. Carefully mix contents.
- Record results in Table 1.3 – Starch Test Data Table.
- Pour out contents and wash test tubes.
Part 3: Testing for Proteins
- Using the graduated cylinder, add 10 mL of distilled water to the control test tube. Add 5 drops of Biuret to the test tube. Carefully mix the contents.
- Record the colour of the solution in Table 1 – Control Results. You now know what colour the solution will be if no proteins are present in a sample.
- Using the same foods as tested in Part 1, add a small amount to the already labelled test tube.
- Add 5 drops of iodine Biuret to each test tube. Carefully mix contents.
- Record results in Table 1.4 – Protein Test Data Table.
- Pour out contents and wash test tubes.
Part 4: Testing for Lipids
- Using the graduated cylinder, add 10 mL of distilled water to the control test tube. Add 5 drops of Sultan IV to the test tube. Carefully mix the contents of the test tube.
- Record the colour of the solution in Table 1 – Control Results. You now know what colour the solution will be if no lipids are present in a sample.
- Using the same foods as tested in Part 1, add a small amount to the already labelled test tube.
- Add 5 drops of Sultan IV to each test tube. Carefully mix contents.
- Record results in Table 1.3 – Lipid Test Data Table.
- Pour out contents, wash test tubes and place in drying rack.
Analysis Questions: Answer each of the following in complete sentences and paragraph form (one paragraph for each).
- Describe the stain that is used to test for the presence of mono/disaccharides?What colour indicates a negative result for mono/disaccharides? What colour indicates a positive result? Which of your samples tested positive for mono or disaccharides?
- Describe the stain that is used to test for the presence of polysaccharides? What colour indicates a negative result? What colour indicates a positive result? Which of your sample tested positive for polysaccharides?
- Same as above for proteins.
- Same as above for lipids.
Conclusion Questions:
- Why do experimental procedures include control samples?
- Assume you have tested an unknown sample with both Biuret Reagent and Benedict’s solution and that both tests result in a blue colour. What have you learned?
Lab Reports:
All Lab Reports must be typed. It should include:
- Title, name, date, course, and teacher.
- Purpose
- Materials
- Procedure: “refer to handout: Lab Activity #1: Testing for Macromolecules.”
- All data tables.
- Analysis questions.
- Conclusion.
Lab Report is due: ______