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Detecting Fats and Starches in Food (2 Favorites)

LAB in Molecular Structure, Chemical Change. Last updated May 24, 2017.


Summary

In this lab, students will identify fats and starches in a variety of foods. Since we eat many complex foods which contain mixtures of carbohydrates (e.g. sugars and starches), fats, and proteins, conducting food tests will enable the students to determine what a certain food is made up of.

Grade Level

Middle School

Objectives

By the end of this lab, students should be able to
  • Determine if a food contains starch and/or fats.
  • Distinguish between a starch and a fat.
  • Understand the chemical reaction between iodine and starches.

Chemistry Topics

This lab supports students’ understanding of
  • Chemical Reactions
  • Chemical Change
  • Molecular Structure
  • Identification of an Unknown
  • Qualitative Analysis

Time

Teacher Preparation: 30 minutes

Lesson: 60 minutes

Materials (per group)

  • 1 piece of wax paper (20x20 cm) or a microplate (microplate)
  • 1 Eyedropper
  • Tincture of Iodine (Iodine safety data)
  • 1 Brown paper bag
  • 1 Marker
  • Tweezers
  • 4 plastic knives
  • Measuring spoons (1/4 and 1/8 teaspoons)
  • Knife (teacher use)
  • Scissor (teacher use)
  • Testing Samples (per group):
    • 2 Cheese samples cut in ¼ inch pieces
    • 2 Bread samples cut in ½ inch pieces
    • 2 Cracker samples cut in ¼ inch pieces
    • ¼ teaspoon of Rice
    • 1 raw potato cut in ¼ inch piece
    • 1/8 teaspoon of liquid cooking oil
    • ¼ teaspoon of flour
    • ¼ teaspoon of starch
    • 1 hot dog cut in ¼ inch piece
    • 1/8 teaspoon of butter
    • 1/8 teaspoon of margarine
  • Safety goggles
  • Apron
  • Gloves

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • Food in the lab should be considered a chemical not for consumption.
  • Caution: Iodine is poisonous. Do not allow iodine to get on your hands. Wear gloves at all times. Wash immediately if iodine comes in contact with your skin, Iodine safety data sheet

Teacher Notes

  • Students should work in pairs.
  • This lab provides the opportunity to introduce students to the following vocabulary words and topics:
    • Chemical reaction: a process where atoms of the reactant(s) will rearrange themselves to create a new arrangement of atoms, called the product.
    • Reactant: A substance or substances present at the start of the reaction.
    • Product: A resulting substance or substances formed by a chemical reaction.
    • Chemical Change: Any change that result in the formation of a new substance or substances.
    • Indicator of chemical change or chemical reaction in this lab: change of color.
  • Pre-cut the pieces of potato, cheese, cracker, hot dog, bread, butter, and margarine.
  • Pre-measure the amount of starch, flour, and liquid oil.
  • Pre-cut the 20x20 cm piece of wax paper
  • I suggest that the teacher places properly labelled samples on a table for students to pick up.

Background & Results

  • Starches are carbohydrates. Carbohydrates provide energy for the body. Fats are lipids. Your body needs more carbohydrates than fats and proteins each day. The simplest test for the presence of fats is to rub the food on brown paper. If a translucent spot occurs where the food touched the paper, this shows that fats are present. In order to test for the presence of starch, a solution of iodine is dropped onto the starch containing food. If a color change from deep red to purple/black occurs, this indicates the presence of starch. The reason for this change is that the iodine molecules non-covalently interact with the long starch molecules and this alters the color obtained.

For the Student

Background

In this lab, you will identify fats and starches in a variety of foods. We eat many complex foods which contain mixtures of carbohydrates (e.g. sugars and starches), fats, and proteins. Conducting a food test will enable you to find out what the food is made up of. Starches are carbohydrates, and carbohydrates provide energy for the body. Fats are lipids. Your body needs more carbohydrates than fats and proteins each day.

The simplest test for the presence of fat is to rub the food on brown paper. If a translucent spot occurs where the food touched the paper, then this indicates that fat is present. In order to test for the presence of starch, a solution of iodine is dropped onto the food. A color change from deep red to purple/black indicates the presence of starch. The reason for this change is that the iodine molecules non-covalently interact with the long starch molecules and this alters the color.

Pre-lab Questions

  1. What is a starch?
  2. What is a carbohydrate?
  3. What is a lipid?
  4. What is a fat?

Hypothesis:

Objective

You will determine which foods contain fat and which foods contain starch.

Materials

  • Safety goggles
  • Apron
  • Gloves
  • Wax paper or a microplate
  • Eyedropper
  • Tincture of Iodine
  • Brown paper bag
  • Marker
  • Pencil
  • Tweezers
  • Plastic knives
  • Testing Samples:
    • Cheese
    • Bread
    • Cracker
    • Rice
    • Potato
    • Cooking Oil
    • Flour
    • Starch
    • Hot dog
    • Butter
    • Margarine

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • Follow teacher instructions for clean-up of materials and disposal of any chemicals.
  • Food in the lab should be considered a chemical not for consumption.
  • Caution: Iodine is poisonous. Do not allow iodine to get on your hands. Wear gloves at all times. Wash immediately if iodine comes in contact with your skin.

Procedure

  1. Write a hypothesis predicting which food items listed in the material list contain starch and which contain fat. Justify your prediction with reasoning (explain why!)
  2. Collect the food items you will test.
  3. Place the food items on the wax paper or the testing dish.
  4. Label each food item, using the marker.
  5. Using a plastic knife, rub each food sample on the brown paper bag to test for fats. A translucent spot indicates the presence of fats.
  6. Place a small drop of iodine on each item tested for the presence of starch.
    A blue/black color indicates the presence of starch.
  7. Write your results in the data table provided.

Data

Food Item

Iodine test results

Brown Bag Test results

Starch

Cheese

Bread

Cracker

Rice

Potato

Liquid cooking oil

Flour

Hot Dog

Butter

Margarine

Analysis

  1. Which foods tested showed the presence of starch?
  2. Explain how do you know that the foods listed above contain starch:
  3. Why was starch tested for the presence of starch?
  4. Which foods tested showed the presence of fats?
  5. Explain how you know that the above foods contain fats:
  6. Were you surprised about any of the results? Why or why not?

Conclusion

  1. Was your hypothesis accepted or rejected? Explain why.
  2. What did you learn from these experiments that you did not know before? (Write at least three full sentences)