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Laboratory Instructions
Laboratory: Investigating Biological Compounds
Materials
Supplied
Laboratory Instructions
Laboratory Guidelines
Investigating Biological Compounds Virtual Lab (online)
Safety
Review the Laboratory Guidelines before conducting the lab.
Overview
Pure cocaine powder is often diluted or “cut” by mixing it with other white powders, such as cornstarch, flour, powdered milk, crushed vitamins, aspirin, or other white, powdered drugs. How can investigators distinguish among these powders? Simple chemical tests provide useful clues.
In this lab, you are a forensic chemist. Police have seized 150 pounds of a substance (later proven to be cocaine) from a hotel room in Oceanside, CA, near San Diego. They have sent a sample of the cocaine to your lab to identify whether certain biological compounds were used to cut the cocaine. The DEA suspects one of three organizations: one located in San Diego, one in Los Angeles, and one in Bakersfield. Each organization has its own preferred “cutting” powder.
• San Diego – powdered milk
• Los Angeles – cornstarch
• Bakersfield – ascorbyl palmitate, a fat-soluble form of vitamin C.
In this lab, you will run tests on an unknown sample to determine whether protein, starch, or lipid is present in the seized cocaine. The results will provide clues to the organization responsible for the crime.
Procedure
Part 1: Introduction
1. Open the Investigating Biological Compounds Virtual Laboratory.
2. Click View the Tutorial.
3. Complete the tutorial to learn how to use the lab. The tutorial will walk you through the key procedures of the virtual lab. Knowing a few basic procedures will allow you to complete the procedures below.
4. When you have finished the tutorial, click the home button, reset the lab, click Begin the Lab, and proceed to the sections below.
Part 2: Test for Starch
1. When starch is present, an iodine solution will turn dark blue, dark violet, or even almost black. Knowing this, you can conduct a procedure on your own using the solutions in the lab. If you wish, you may follow the procedures in Steps 2–4.
2. Place water from a filled pipette into the test tube labeled “Starch Control (water).”
3. Place starch from a filled eyedropper into the test tube labeled “Test for Starch.”
4. Test for starch by adding iodine from a filled eyedropper to each test tube. Record your observations in the table below. Answer the question.
|Test Tube |Observation |
|Starch Control (water) | |
|Test for Starch | |
5. Why do we say that an iodine solution is an indicator for starch?
Part 3: Test for Protein
1. When protein is present, a mixture of sodium hydroxide and copper sulfate will turn a very dark color. Knowing this, you can conduct a procedure using the solutions in the lab. If you wish, you may follow the procedures in Steps 2–4.
2. Place water from a filled pipette into the test tube labeled “Protein Control (water).”
3. Place milk from a filled pipette into the test tube labeled “Test for Protein.”
4. Test for protein by adding copper sulfate from a filled eyedropper and sodium hydroxide from a filled eyedropper to each test tube. Record your observations in the table below. Answer the question.
|Test Tube |Observation |
|Protein Control (water) | |
|Test for Protein | |
5. Why do we say that the basic solution containing copper sulfate is an indicator solution for protein?
Part 4: Test for Lipids
1. When lipids, such as vegetable oil, are present, a Sudan III solution will turn orange or red. Knowing this, you can conduct a procedure using the solutions in the lab. If you wish, you may follow the procedures in
Steps 2–4.
2. Place water from a filled pipette into the test tube labeled “Lipid Control (water).”
3. Place vegetable oil from a filled pipette into the test tube labeled “Test for Lipid.”
4. Test for lipid by adding Sudan III from a filled eyedropper to each test tube. Record your observations in the table below. Answer the question.
|Test Tube |Observation |
|Lipid Control (water) | |
|Test for Lipid | |
5. Why do we say that Sudan III is an indicator solution for lipid?
Part 5: Test for Unknown
The unknown sample in the virtual lab is the Oceanside cocaine sample. Your job is to test the sample to see whether it contains protein, starch, or lipid. This may provide a link to the organization responsible for the seized cocaine.
Knowing this, you can conduct a procedure using the solutions in the lab. If you wish, you may follow the procedures that you see here in Steps 1–4.
1. Place the unknown sample from a filled eyedropper into the test tube labeled “Unknown (starch).”
2. Place the unknown sample from a filled eyedropper into the test tube labeled “Unknown (protein).”
3. Place the unknown sample from a filled eyedropper into the test tube labeled “Unknown (lipid).”
4. Add the appropriate indicator solution to each test tube. Record your observations in the table below.
|Test Tube |Observation |
|Unknown + Starch Indicator | |
|Unknown + Protein Indicator | |
|Unknown + Lipid Indicator | |
5. Which test tube showed a completely positive response to an indicator solution?
Analyze Your Results
1. Were the results of this test evidence that was individualized or class evidence?
2. The lipids in milk will cause the milk to react strongly with Sudan III. If you knew that milk also contained some sugars, how might this lead to testing errors?
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