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Using a third dropping pipet, add 10 drops of distilled water to the "1-water" test tube. Mix the contents of each test tube with a clean stirring rod. (It is important not to contaminate test solutions by using the same dropping pipet or stirring rod in more than one solution. Use a different dropping pipet and stirring rod for each of the test solutions.)

4. When the water boils, use tongs to place the test tubes in the water bath. Boil the test tubes for 1 to 2 minutes.

5. ^V CAUTION Do not touch the test tubes with ^ your hands. They will be very hot. Use tongs to remove the test tubes from the water bath and place them in the test-tube rack. As the test tubes cool, an orange or red precipitate will form if large amounts of glucose are present. If small amounts of glucose are present, a yellow or green precipitate will form. Record your results in your data table.

Test 2: Proteins

6. J^ Label one clean test tube "2-albumin," label V a second test tube "2-unknown," and label a third test tube "2-water." Using a dropping pipet, add 40 drops of albumin solution to the "2-albumin" test tube. Using a second dropping pipet, add 40 drops of unknown solution to the "2-unknown" test tube. Using a third dropping pipet, add 40 drops of water to the "2-water" test tube.

7. Add 40 drops of sodium hydroxide solution to each of the three test tubes. Mix the contents of each test tube with a clean stirring rod.

8. Add a few drops of copper sulfate solution, one drop at a time, to the "2-albumin" test tube. Stir the solution with a clean stirring rod after each drop. Note the number of drops required to cause the color of the solution in the test tube to change. Then, add the same number of drops of copper sulfate solution to the "2-unknown" and "2-water" test tubes.

9. Record your results in your data table.

Test 3: Lipids

10. Label one clean test tube "3-vegetable oil," label a second test tube "3-unknown," and label a third test tube "3-water." Using a dropping pipet, add 5 drops of vegetable oil to the "3-vegetable oil" test tube. Using a second dropping pipet, add 5 drops of the unknown solution to the "3-unknown" test tube. Using a third dropping pipet, add 5 drops of water to the "3-water" test tube.

11. ^^ CAUTION Sudan III solution will stain your ^ skin and clothing. Promptly wash off spills to minimize staining. Do not use Sudan III solution in the same room with an open flame. Using a clean dropping pipet, add 3 drops of Sudan Ill solution to each test tube. Mix the contents of each test tube with a clean stirring rod.

12. Record you results in your data table.

13. Jit^ A Clean up your materials, and wash your ^^ hands before leaving the lab.

Analysis and Conclusions

1. Based on the results you recorded in your data table, identify the nutrient or nutrients in the unknown solution.

2. What are the experimental controls in this investigation?

3. Explain how you were able to use the color changes of different indicators to determine the presence of specific nutrients in the unknown substance.

4. List four potential sources of error in this investigation.

Further Inquiry

Is there a kind of macromolecule that the tests in this lab did not test for? If so, list the kinds of macromolecules not tested for, and give one reason why they were not tested for.

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