SBI4U: TESTING FOR CARBOHYDRATES, FATS AND PROTEINS

Materials

Benedicts solution Beakers

Biuret reagent Hot plate

Dextrose Test tubes

Iodine Test tube rack

Paper towel Egg white

oil

My sample______

Safety Considerations: wear safety glasses

Biurets and Benedicts can cause an itchy rash upon skin contact-rinse thoroughly

Iodine can stain skin and clothing-work with care

Method

See below for the positive tests for each nutrient

POSITIVE TESTS

Part A:Monosaccharide Test

1.  Put 1 finger width of dextrose into a clean test tube.

2.  Add 3-4 drops of Benedicts solution to the tube.

3.  Boil the tube in a hot water bath for 2 minutes.

4.  Observe and record any colour change.

5.  Use chart below to determine the approximate sugar concentration in your sample.

Colour with Benedicts / Approximate Sugar concentration of Sample
Blue / Nil
Light Green / 0.5-1.0%
Green to Yellow / 1.0-1.5%
Orange to Yellow / 1.5-2.0%
Red to Red brown / 2.0% ++

Part B: Starch Test

1.  Put 1 finger width of the starch suspension into a clean test tube.

2.  Add 3-4 drops of Iodine solution into the tube.

3.  Observe and record any colour change.

Part C: Protein Test

1.  Put 1 finger width of the egg white into a clean test tube.

2.  Add 3-4 drops of Biurets solution into the tube.

3.  Observe and record any colour change. Check page 44. (part 5) to see the approximate protein concentration in your sample.

Part D: Fat Test

1.  Put a drop of oil on a piece of brown paper towel and note what happens.

2.  Put a drop of water beside the spot where #1 was completed note what happens.

3.  Wait for 10 minutes and note any changes.

Part D: My sample

1.  Use tests A-D to determine the nutrients present in your own sample.

OBSERVATIONS TABLE

Fill in the blank spots of the observations table with appropriate colour changes

Monosaccharide
(Benedicts) / Starch
(Iodine) / Protein
(Biuret) / Fat
(paper towel)
Dextrose / xxxxxxxxxxx / xxxxxxxxxx / xxxxxxxxxxxx
Starch / xxxxxxxxxx / xxxxxxxxx / xxxxxxxxxxxxx
Egg white / xxxxxxxxxx / xxxxxxxxxxx / xxxxxxxxxxxxx
Oil / xxxxxxxxxxx / xxxxxxxxxxx / xxxxxxxxxxx
My sample
______

QUESTIONS

1. List possible sources of error in this lab and indicate how you could improve the method.

2. What would happen if Abdou put a sugar cube in the eggwhite solution? How might this skew results?

3.Nada accidentally drops on a piece of paper from your notebook. Predict the colour change and account for your reasoning.

4. Danielle heats a tube containing a large amount of protein and Biurets reagent. She notices the colour changes from violet to blue. Explain why this happens.

5. Are the results from your food sample reasonable? Explain why or why not.