Jump to main content

Crime Scene Chemistry: Determine the Identity of an Unknown Chemical Substance

1
2
3
4
5
407 reviews

Abstract

Picture this situation: An elderly woman is rushed to the hospital complaining of severe abdominal pain, tinnitus, and lethargy. Suspecting a drug interaction, the emergency room doctor starts questioning her. The doctor learns that the woman takes no medicines except aspirin for her arthritis. Since she cannot swallow pills well she takes a powdered form of aspirin which she buys in bulk and keeps in a plastic container in her kitchen next to her baking goods. She had just finished a day of baking sweets for her grandchildren when she felt poorly. She admits that she often samples while she bakes and thought that she had just had too many sweets. Immediately the doctor suspects that she has mixed up the aspirin and another ingredient and is suffering from aspirin poisoning. The doctor quickly pumps her stomach. Soon the woman is feeling well again, but the doctor needs to confirm the diagnosis before releasing her. If the doctor is wrong, the woman could be suffering from something far more severe. If the doctor is right, the poisoning could easily occur again unless the aspirin is located and properly labeled. In this chemistry science fair project you will perform a series of tests on the woman's baking goods to help solve the mystery of what happened.

Summary

Areas of Science
Difficulty
 
Time Required
Very Short (≤ 1 day)
Material Availability
A kit is available from our partner Home Science Tools. See the Materials section for details.
Cost
Average ($40 - $80)
Safety
Wear disposable gloves when working with chemicals.
Credits

David Whyte, Ph.D. and Sandra Slutz, Ph.D., Science Buddies

Recommended Project Supplies

Get the right supplies — selected and tested to work with this project.

View Kit

Objective

Perform chemical analysis to identify the nature of an unknown powder. This is an example of forensic chemistry.

Introduction

The branch of chemical analysis that focuses on crime scenes is called forensic chemistry. A forensic chemist is challenged with questions such as: "Is this white powder an illegal drug, or is it just sugar?"; "Is there poison in the blood of this potential homicide victim?"; and "Is there chemical evidence for arson in this fire investigation?"

In this chemistry science fair project, you will act as a forensic chemist to determine if an elderly woman accidentally consumed toxic levels of aspirin. Here is the scenario: An elderly woman is rushed to the hospital complaining of severe abdominal pain, tinnitus, and lethargy. Suspecting a drug interaction, the emergency room doctor starts questioning her. The doctor learns that the woman takes no medicines except aspirin for her arthritis. Since she cannot swallow pills well she takes a powdered form of aspirin which she buys in bulk and keeps in a plastic container in her kitchen next to her baking goods. She had just finished a day of baking sweets for her grandchildren when she felt poorly. She admits that she often samples while she bakes and thought that she had just had too many sweets. Immediately the doctor suspects that she has mixed up the aspirin and another ingredient and is suffering from aspirin poisoning. The doctor quickly pumps her stomach. Soon the woman is feeling well again, but the doctor needs to confirm the diagnosis before releasing her. If the doctor is wrong, the woman could be suffering from something far more severe. If the doctor is right, the poisoning could easily occur again unless the aspirin is located and properly labeled.

Your role as the forensic chemist is to use four tests to determine if ingredients labeled sugar, salt, and cornstarch in her kitchen are aspirin instead. To do this, you will compare a known sample of aspirin (known samples are called controls in science) to the three unknown samples (presumed to be sugar, salt, and cornstarch) collected from the lady's home. You will investigate the following properties for the test substances: physical appearance , solubility in water, reaction with iron nitrate (the reaction produces a deep purple color if aspirin is present), and reaction with Lugol's iodine (the reaction produces a blue-black color when starch is present). There are five possible outcomes to your testing: 1) None of the unknowns are aspirin 2) the unknown presumed to be sugar is aspirin 3) the unknown presumed to be salt is aspirin 4) the unknown presumed to be cornstarch is aspirin 5) more than one of the unknowns is aspirin. Do a bit of background reading about each test and then diagram out what you expect the test results to look like for each of the five possible outcomes. Do you think you will have enough data from the four tests to determine if any of the unknowns is actually aspirin?

Terms and Concepts

Questions

Bibliography

This paper is a little advanced, but it has good information about the iron test for aspirin.

Materials and Equipment Buy Kit

Recommended Project Supplies

Get the right supplies — selected and tested to work with this project.

View Kit

Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools, Amazon.com, Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student learning. If you have any comments (positive or negative) related to purchases you've made for science projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

Experimental Procedure

  1. The kit contains three samples marked unknown. According to the scenario in the Introduction, these were taken from an ill elderly lady's kitchen from the containers where she supposedly keeps her sugar, salt, and cornstarch for baking. But the doctor is concerned that one of them may be aspirin instead. Your task is to determine if any of the unknown samples are aspirin. Based on your background reading, do you think you'll be able to determine this using the tests described below? Why or why not?
  2. Put on a pair of disposable gloves.
  3. Place a reaction plate on your work surface.
  4. Use the wax pencil (or a permanent marker) to label each column of wells as follows:
    1. C, for control, which in this case, is aspirin.
      • The other samples may be "mislabeled," but this control sample is known for sure to be aspirin.
    2. Su, for sugar
    3. Sa, for salt
    4. CS, for cornstarch
  5. Label the first three rows of the reaction plate, as follows:
    1. Water
    2. Iron
    3. Iodine
  6. The reaction plate should look like Figure 1:


Drawn diagram of a reaction plate

Figure 1. Reaction plate for "crime scene" analysis.



  1. Place a small scoopful of the appropriate substance to be tested in each of the wells for the labeled column. Use a clean toothpick as a "scoop" for each substance. The sample marked aspirin should go in the aspirin column. The unknown sample presumed to be sugar should go in the sugar (Su) column. The unknown sample presumed to be salt should go in the salt (Sa) column, and the unknown sample presumed to be cornstarch should go in the cornstarch (CS) column.
    1. The sample marked aspirin should go in the aspirin column.
    2. The unknown sample presumed to be sugar should go in the sugar (Su) column.
    3. The unknown sample presumed to be salt should go in the salt (Sa) column.
    4. The unknown sample presumed to be cornstarch should go in the cornstarch (CS) column.
  2. Record your physical observations of each powder in your lab notebook.
    1. Record color, whether the substance appears crystalline or not, and any other characteristics you can identify.
    2. Do any of the unknown substances have the same physical characteristics as aspirin?
  3. Add several drops of water to each substance in the row labeled Water. Mix each sample gently with a clean toothpick. Use a different toothpick for each sample so you do not contaminate any of them!
  4. Record your observations for each substance in your lab notebook. Do any of the unknowns behave like the aspirin sample when mixed with water? If so, which one(s)? Do any act differently? Which one(s) and how so?
  5. Add two or three drops of NaOH (sodium hydroxide) solution to each sample in the row labeled Iron. Mix each sample gently with a different clean toothpick.
  6. Wait 5–10 seconds and add two or three drops of iron nitrate solution to each sample in the row labeled Iron.
    1. Sodium hydroxide reacts with aspirin to form salicylic acid and acetic acid. Salicylic acid has the interesting ability to cause iron (Fe III) to turn blue/purple. So to test for aspirin in an unknown sample, you first treat the sample with sodium hydroxide, to convert any aspirin in the sample to salicylic acid, then add iron. If a blue/purple color forms, then the test is positive for aspirin!
  7. Record your observations for each substance in your lab notebook. Do any of the unknowns behave like the aspirin sample? If so, which one(s)? Do any samples react differently? If so note which one(s) and how they react.
  8. Place two or three drops of Lugol's iodine in the row labeled Iodine.
  9. Record your results in your lab notebook. Do any of the unknowns behave like the aspirin sample? If so, which one(s)? Do any samples react differently? If so, note which one(s) and how they react.
  10. Perform the procedure two more times with clean materials. This will show that your results are repeatable.
    1. To dispose of the reaction plates, wipe up each liquid on the plate with a paper towel and place the paper towels and the reaction plates in a regular trash.
    2. If you would like to re-use the reaction plates (for example, to do the optional experiment in step 17 below) simply wash the wiped up reaction plates with soap and water.
  11. Analyze your results and make a table. What does each test tell you about the unknown substances? Are any of them aspirin?
    1. You may need to do some research about the tests in order to answer this question.
  12. Optional: Compare known samples of sugar, salt, and cornstarch from your own kitchen with the unknown samples in the kit. Compare both their physical appearances and how they react to the three tests: water, iron, and Lugol's iodine. Is it possible to know from your observations exactly what each substance is? Why or why not?
icon scientific method

Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Global Connections

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.

This project explores topics key to Industry, Innovation and Infrastructure: Build resilient infrastructure, promote sustainable industrialization and foster innovation.

Variations

  • Run the tests on salt, sugar, cornstarch, and aspirin from around your house. Do you get the same results? (Since one of the containers was mislabeled, one of the chemicals was not actually tested. This step fills in the missing data).
  • Modify the procedure so that you can estimate how much aspirin is present in a mixture of aspirin and sugar. Hint: The color produced by the iron test is proportional to the aspirin concentration.

Careers

If you like this project, you might enjoy exploring these related careers:

Career Profile
Guilty or not guilty? The fate of the accused in court lies with the evidence gathered at the crime scene. The job of the forensic science technician is to gather evidence and use scientific principles and techniques to make sense of it. It can be a grueling and graphic job, but very rewarding. If you like the idea of using science to help deliver justice, then you should investigate this career. Read more
Career Profile
Everything in the environment, whether naturally occurring or of human design, is composed of chemicals. Chemists search for and use new knowledge about chemicals to develop new processes or products. Read more
Career Profile
The role that the chemical technician plays is the backbone of every chemical, semiconductor, and pharmaceutical manufacturing operation. Chemical technicians conduct experiments, record data, and help to implement new processes and procedures in the laboratory. If you enjoy hands-on work, then you might be interested in the career of a chemical technician. Read more

Contact Us

If you have purchased a kit for this project from Science Buddies, we are pleased to answer your questions.

In your email, please follow these instructions:
  1. What is your Science Buddies kit order number?
  2. Please describe how you need help as thoroughly as possible:

    Examples

    Good Question I'm trying to do Experimental Procedure step #5, "Scrape the insulation from the wire. . ." How do I know when I've scraped enough?
    Good Question I'm at Experimental Procedure step #7, "Move the magnet back and forth . . ." and the LED is not lighting up.
    Bad Question I don't understand the instructions. Help!
    Good Question I am purchasing my materials. Can I substitute a 1N34 diode for the 1N25 diode called for in the material list?
    Bad Question Can I use a different part?

Contact Us

News Feed on This Topic

 
, ,

Cite This Page

General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "Crime Scene Chemistry: Determine the Identity of an Unknown Chemical Substance." Science Buddies, 29 July 2023, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Chem_p093/chemistry/how-to-identify-a-chemical-unknown. Accessed 28 Mar. 2024.

APA Style

Science Buddies Staff. (2023, July 29). Crime Scene Chemistry: Determine the Identity of an Unknown Chemical Substance. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Chem_p093/chemistry/how-to-identify-a-chemical-unknown


Last edit date: 2023-07-29
Top
We use cookies and those of third party providers to deliver the best possible web experience and to compile statistics.
By continuing and using the site, including the landing page, you agree to our Privacy Policy and Terms of Use.
OK, got it
Free science fair projects.