Carbon Chemistry – Testing for Nutrients in Foods



Organic Compounds – Testing for Nutrients in Foods

Background information

Nutrients in the foods we eat are organic compounds. There are three major types of organic nutrients, namely carbohydrates, proteins, and lipids which are fats and oils. Carbohydrates are polymers made up of the sugar, glucose. Proteins are made up of long chains of amino acids.

Since these three nutrient groups contain different functional groups they will react differently to certain chemical reagents and as such can easily be separated by simply reacting them with these reagents. Iodine solution changes when mixed with starch, while a mixture called Benedict’s solution changes color in the presence of different types of sugars. Biuret solution, which is a solution of copper sulfate changes color when added to proteins. Sudan IV which is a bright red dye dissolves in lipids, but not in water. So any nutrient that Sudan IV dissolves in will be confirmed as containing lipids.

Problem/ Question

Which of the foods contain sugar, starch, protein and lipids?

Pre-Lab Discussion:

We shall read the whole investigation together. Then working with a partner, you will answer the following questions.

1. Making Predictions: Which of the foods provided do you think will react with each of the test reagents? Explain your answer.

i. Benedict’s solution

____________________________________________________________________

________________________________________________________________________________________________________________________________________________

ii. Iodine solution

________________________________________________________________________________________________________________________________________________

iii. Biuret solution

________________________________________________________________________________________________________________________________________________

iv. Sudan IV dye

________________________________________________________________________________________________________________________________________________

2. Predictions:

Which nutrients do you think are present in each food that you will test in Part B of experiment?

i. Orange juice

__________________________________________________________________

ii. Potato

__________________________________________________________________

iii. Whole milk

__________________________________________________________________

iv. Skim milk

__________________________________________________________________

v. Margarine

__________________________________________________________________

vi. Egg white

__________________________________________________________________

vii. Egg yolk

__________________________________________________________________

3. Identify Variables in Part A of this investigation.

i. Manipulated variables

__________________________________________________________________

ii. Responding variables

__________________________________________________________________

iii. Controlled variables

__________________________________________________________________

4. Controlling variables: Why is a test tube of water included with the other 4 test tubes in Part A? Explain your answer.

Designing Experiment:

Describe some procedure you could use to test the predictions you made for Part B.

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Materials

500-mL beaker tongs

hot plate iodine solution

paper towel clock or timer

glass-marking pencil Sudan IV dye

5 test tubes test tube stoppers

test tube rack biuret reagent

4 spatulas orange juice

glucose minced potato

corn starch whole milk

powdered gelatin skim milk

2 dropper pipets margarine

vegetable oil egg yolk

3, 10-mL graduated cylinders egg white

Benedict’s solution

Safety Precautions

Put on safety goggles and a lab apron. Put o a pair of gloves to protect you from direct contact with these chemicals some of which might be irritating or dangerous when in contact with the skin. Be careful when working with glass ware to avoid breakage. If any breakage occurs let the teacher know. Be careful when working with hot surfaces and do not handle electrical connections with wet hands. Do not taste anything during this investigation unless told to do so by teacher.

*Special note for ELL students: The teacher has to read the procedure and explain vocabularies with students. In addition a demonstration of the step by step procedure is done by teacher before students start the procedure.

Part A : Observing Chemical tests for the nutrients

1. Put about 125-mL water in the 500-mL beaker. Place the beaker on the hot plate. Bring the water to a boil by turning the hot plate on to high setting. Be careful when handling hot water and the hot plate also.

2. Label each test tubes, writing glucose on test tube 1, corn starch on tube 2, gelatin on test tube 3, and vegetable oil on test tube 4, and only number 5 on test tube 5. Using a separate clean and dry spatula each time, add just enough of glucose to cover the end of the spatula into test tube 1, same amount of corn starch into test tube 2, and same amount of gelatin into test tube 3. Use a dropper pipet to add 4 drops of vegetable oil into test tube 4. Store the spatulas on labeled spots on a clean paper towel.

3. Use a graduated cylinder to place 3-mL water into each of the 5 test tubes..

4. Fill each of the test tubes half way with Benedict’s solution.

5. Using tongs place the 5 test tubes in the boiling water I the beaker. Leave them in for 5 minutes.

6. At the end of 5 minutes, use tongs to transfer the test tubes from the beaker onto the test tube rack. Observe any changes in the appearance of the contents of each tube and record your observations in data table 1.

7. Pour away the content of the contents of the five test tubes in the sink and thoroughly wash the five test tubes carfully dry the tubes and place them back in the test tube rack.

8. Repeat steps 2 and 3.

9. Use a dropper pipet to add 1 or 2 drops of iodine solution to each test tube. Observe to see if there is any change in the brown color of iodine to another color. Record your observation on table 1.

10. Wash an dry the tubes again. Then repeat steps 2 and 3.

11.Use a clean spatula to place a few grains of Sudan IV dye into each test tube. Be careful not to get dye on your skin or clothing.

12. Place a stopper firmly on the test tubes and shake carefully to avoid spilling. Observe and rcord any changes in the appearance of the contents of the test tubes in data table 1.

13. Wash and dry test tubes and repeat steps 2 and 3. Us e a clean dropper pipet to place 3 drops of biuret reagent in each test tube. Observe any changes to the content of the test tubes and record them in the data table 1. Be careful with Biuret reagent. It can burn and stain the skin and clothing.

Part B: Using Chemical Tests to Identify Nutrients

14. Design an experiment to test the predictions you made in Pre-Lab Discussion question 2. Write a detailed plan of how you are going to carry out your experiment. Use the information or observations you made from the chemical testing of organic nutrients from Part A of this investigation to help you plan your procedures. Construct data table 2

to record your observations.

15. Identify the manipulated, responding and controlled variables in your investigation.

i. Manipulated variables

__________________________________________________________________

__________________________________________________________________

ii. Responding variables

__________________________________________________________________

__________________________________________________________________

iii. Controlled variables

__________________________________________________________________

__________________________________________________________________

16. What safety precautions are you going to take?

__________________________________________________________________

17. Show your written plan to your teacher for approval, before doing experiment.

Results

Data Table 1

|Test Tube |Food |Benedict’s solution |Iodine solution |Sudan IV dye |Biuret reagent |

|1 |Sugar | | | | |

|2 |Corn starch | | | | |

|3 |Gelatin | | | | |

|4 |Vegetable oil | | | | |

|5 |Water | | | | |

Data Table 2

Analysis and Conclusions

1. Observing: Which foods reacted with Benedict’s solution in Part B?

___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. Observing: Which food(s) reacted with iodine solution?

_________________________________________________________________________________________________________________________________________________________________

3. Analyzing data: What color change did you observe in the biuret solution test? Which foods caused this change?

___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

4. Analyzing Data: What change did you observe in the Sudan IV dye test? Which foods caused this change?

_________________________________________________________________________________________________________________________________________________________________________________________________________________________

5. Comparing and Contrasting: Based on your data from Part B, what is the major difference between whole milk and skim milk?

______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

6. Comparing and Contrasting: Which nutrient did you find in the egg yolk that you did not find in the egg white?

___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

7. Evaluating and Revising: Which of your predictions did your data support?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

8. Drawing Conclusions: Human babies grow rapidly and are healthy even when milk is the only source of nutrition they get. Explain why this is possible

_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download