Carbohydrates, Lipids, Proteins

1. Suppose that you were given a sample and wanted to know if it contained starch. What could you do to determine if the sample contained starch?

2. Suppose that you had a solution in a test tube and wanted to know what kinds of compounds it contained. You add Benedict’s reagent and place the tube in a boiling water bath for 5 minutes and the solution turns red. What would you conclude about the chemical composition of the solution?

3. Benedicts reagent  was added and the solution was boiled for 5 minutes.  The solution changed color.

   a) protein     b) starch     c) reducing sugars     d) lipids

4. IKI was added and it turned purple-black.

   a) protein     b) starch     c) reducing sugars     d) lipids

5. A drop of the substance was placed on paper and it was immediately absorbed by the paper.  It did not evaporate.

   a) protein     b) starch     c) reducing sugars     d) lipids     e) water

6. What was the effect of the emulsifier (liquid detergent) on the oil?

7. Microscopic examination of a lipid, emulsifier, and water mixture should reveal that

   a) the oil droplets are smaller than those produced by a lipid and water alone.

   b) the oil droplets disappear after approximately 10 minutes.

   c) the oil droplets are larger than those produced by a lipid and water alone.

   d) the oil droplets change color, indicating the presence of a lipid.

8. Name the bond that holds amino acids together.

9. COOH and NH₂ are found on which types of compounds?
   a) lipids     b) carbohydrates      c) reducing sugars     d) proteins     e) nucleic acids

10. Name and describe the test that we used in lab to test for proteins.

11. A positive Biuret test indicates the presence of
    a) protein     b) starch      c) reducing sugars     d) lipids

12. Suppose that the following tubes are prepared:

    Tube 1: distilled water

    Tube 2 albumin solution

    Tube 3 Starch solution

    Biuret solution is added to each. What will happen to each? Explain why. (answer below)

    Tube 1 –

    Tube 2 –

    Tube 3 –

13. An unknown sample was tested using several of the techniques learned in lab.  Tell what substance is in the sample based on the outcome of the test.

14. What purpose does the water sample serve when you establish a test for a particular compound?