Lyoe Lee
January 2010

Who stole the Playstation?
Teacher’s Instructions

Teaching Objectives:

  • Students will understand the basic concepts of different nutrients in foods
  • Students will chemically test and compare different nutrients using extraction technique
  • Students will observe the presence of various nutrients in foods

Recommended Grades: 5-6th graders

Estimated Time: 50 min

Key concepts and definitions of terms:

Fat: Compounds that are insoluble in water, it provides concentrated source of energy

Protein: Needed to carry out metabolic processes, it builds and repairs tissues

Carbohydrates: Starches and sugars, it provides source of energy

Extraction: Separate a solute from one phase into the other

Materials:

Food:

  • Potato chips (any brand would do)
  • Chicken Nuggets (any kind of meat is good, better to choose fatty parts)
  • Frostings
  • Oranges
  • French Fries

Chemicals:

  • Copper(II) Sulfate& Sodium Hydroxide crystals
  • Iodine solution (commonly found in drug store)
  • Benedict’s solution (Please refer to References)
  • Dry ice (or anything that cools down solution fast)

Additional materials:

  • Mortar and pestle (some device for grinding food, e.g. blender)
  • Stirrer and hot plate
  • Beakers (or small bowls and cups)
  • Water
  • Droppers
  • Test tubes & test tube rack

Safety Information:

  • All foods are safe for kids to touch or smell.
  • All chemicals should be dealt with caution, gloves should be worn, an certified person should be present to supervise the use of chemicals.

Procedures:

  1. Present the mystery/case, a thief stole a Playstation, and left some food crumbs at the crime scene.
  2. Divide work for the kids so that each kid is testing 1 or 2 kinds of food.
  3. Crush one kind of food using mortar and pestle, adding water in the process.
  4. Divide the crushed food equally into 2 beakers, add abundant amount of water.
  5. Heat up one beaker of food with the hot plate. When the solution is warm, extract the solution out to 3 test tubes using a dropper for the extraction.
  6. While waiting for the food to get warm, put the other beaker of food into a huge beaker of water, add dry ice, and let it cool for 20-30min.
    Note: Be careful of the beaker containing the food, as it might topple over when floating in water
  7. Explain the reasoning behind the tests. Continue the discussion by working on answers for the pre-lab questions. (Please refer to Worksheet)
  8. Add a few drops of Copper(II) Sulfate and Sodium Hydroxide to one test tube.
    Note: Be careful in handling these chemicals, gloves should be worn.
  9. Ask each student to observe and record what change is seen, explain what color it would be if a lot of protein is present. (Please refer to Why it works)
  10. Add a few drops of Benedict’s solution into the 2nd test tube, add some iodine solution to the 3rd test tube.
  11. Observe and record what happens to the color of the solution, explain what color it would be if a lot of sugar is present. (Please refer to Why it works)
  12. Return to the beaker that is being cooled. Observe the fat that is floating on top of the solution.
  13. Compare the amount of fat with another kind of food.
  14. Record down the color of the fat. (Please refer to Why it works)
  15. Deduce what is the food that was left in the crime scene by comparing all the tests’ observations with the CSI ‘evidence.’ (Please refer to Worksheet)
  16. Clean-up.

Clean-up:

  • All liquids except with Copper(II) Sulfate can be rinsed down the drain.
  • All left over solutions with Copper(II) Sulfate need to be collected and treated as heavy metal waste.

Additional notes:

  • This experiment can be done with many different foods not already listed above, though some work much better than other. You could ask kids to bring different food from home to experiment with.
  • Also, you could test for starch using iodine solution, if time allows. The procedures are exactly the same, except you have to prepare one more test tube of solution to drop iodine solution in. (Please refer to Why it works)
  • A color code worksheet is attached at the end of the Worksheetto provide students with a better understanding of what is the color change during various tests.
  • You do not have to use the ‘evidence’ given in the worksheet. You can work out a new evidence from another kind of food.

Why it works:

Different food has different concentrations of starch, sugar, fat and protein levels. There are many tests for the presence of these nutrients and their concentrations, and this experiment only presents one of the many ways to do that.

Sugar testing
When Benedict’s solution is added to the solution, it will react with the glucose present in the food, and change color. The color will change from its original color, blue, to green, yellow and brick red, depending on the amount of sugar. The redder the solution, the more sugar is present.

Protein testing
When copper sulfate and sodium hydroxide is added is added to the solution, a chemical reaction takes place, and it will produce a light purple color if protein is present. Furthermore, it will turn light pink if a huge concentration of protein is present.

Fat testing
By using dry ice with water, it cools down the solution quickly. As fat will float on water, cooling the solution will cool down the fat. So, it is relatively easy to identify the fat when it is solidified under cold temperature, as fat freezes above freezing point of water. Also, different kind of oil and ingredients in the food will produce different colors of fat. It is better to test the foods beforehand, and know what color the fat is in order to produce the ‘evidence’ that CSI had left for the students.

Starch testing
When iodine solution is added to the solution, it will react with the starch present to produce a bluish black color. If fried meat is used, usually, there might be starch present as flour is used in frying meat.

References:

The experiment:

Definitions:



Recipe for Benedict’s Solution:

http://faculty.mansfield.edu/bganong/biochemistry/reagents.htm

Purchasing of chemicals:
Copper(II) Sulfate Pentahydrate:

Sodium Hydroxide:

Worksheet

CONFIDENTIAL
CSI MAINE
FILE NO: 521548

Please do not disclose any information to anyone else besides those working in the team before the case is cracked. Please print and sign your name below to if you agree not to disclose any information to others.

Name: ______Signature: ______

Alert! A playstation was stolen from Ms. Montana’s home! When police arrived at the crime scene, they found some evidence left behind by the burglar. CSI Maine has started working on this case, but they need more help. They have analyzed the evidence and recorded down the results, now they need to find out what kind of food it is.

Your job is to team up with CSI Maine to nail down what kind of food the burglar left behind, and thus possibly help with sending the burglar to jail!

Here are the suspects and the food they were eating during the time of burglary.

Name / Food
Artist: Mr. Standley / Chicken Nuggets
Old Man: Mr. Stewart / Potato Chips
Young Girl: Ms. Luftnagle / Banana
Old Woman: Ms. Addison / Orange
Young Man: Mr. Ryan / Cake

Here are the results that CSI obtained from the evidence left in the crime scene.

Tests / Observation
Protein test / Turn light purple
Sugar test / No change of color
Fat test / White and Orange color fats visible
Starch test / Turn dark purple

Pre-lab questions

  1. Which one of the food do you expect to have the most protein? Why?
  1. Do you expect chicken meat to have sugar and starch? Why?

Now record down your observations

Potato Chips

Tests / Observation

Orange

Tests / Observation

Chicken Nuggets

Tests / Observation

Frostings

Tests / Observation

French Fries

Tests / Observation

Now match your observations to the evidence CSI Maine has obtained. Can you deduce what is the food? Who is the burglar?

Color Coding for tests

Test / Color
Nothing / Less / More
Sugar Test / Light Blue / Light Green / Dark Red
Starch Test / Nothing / Light Purple / Dark Purple
Protein Test / Light Blue / Light Purple / Light Pink
Fat Test / N/A / N/A / N/A

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